Friday, July 27, 2007

A Tale of TrueHD

There is probably nothing about the new HD DVD and Blu-ray high-definition disc players more confusing to consumers than how the various "next-generation" digital audio codecs get handled. In this post I'll look into one of the most promising, Dolby TrueHD.

Dolby Labs, creators of TrueHD, are the nice folks that brought you Dolby Digital surround sound, the type of 5.1-channel audio found on the soundtrack of virtually every DVD sold in the U.S. The venerable Dolby Digital 5.1 codec (coder-decoder) offers up to six channels of digitally compressed surround sound: three front channels and two surrounds, complemented by a single Low Frequency Effects channel, the ".1" in the 5.1 designation.

DD sound is digitally compressed as it is being encoded by hardware or software that implements the Dolby Digital 5.1 codec. This happens as a step in the process by which the DVD is "authored." The same codec is implemented in the DVD player or in an outboard A/V receiver fed by the player, this time to decode the DD 5.1 bitstream that has been recorded on the disc.

DD 5.1 compression is "lossy." When the player or receiver decodes the bitstream, the result is not a carbon copy of the original input to the encoder. The ear can hear the difference in subtle, hard-to-define ways. So the Dolby folks looked for ways to up the ante on perceived realism and, not incidentally, to increase the number of available channels of sound from 5.1 to 7.1 (or more) for an even better surround effect.

One way they did this was to enhance lossy Dolby Digital into Dolby Digital Plus. DD+ is still a lossy digital audio compression format, but it is less lossy than DD without the "+", and it can contain 7.1 channels of sound, which DD can't. DD+ audio files on a disc contain more information (more bits) than plain old DD. So the bits have to be read in from the disc, decoded, and otherwise processed at a faster clip (a higher bitrate).

Dolby's next step was to add yet more bits to DD/DD+ to come up with a fully "lossless" digital audio compression format: Dolby TrueHD. Because it's lossless, the output of the decoder is exactly the same as the original input to the encoder. The increase in realism over DD+ or DD is said to be stunning. TrueHD bitrates are necessarily higher than DD+ bitrates.

Handling TrueHD

When an HD player, be it HD DVD or Blu-ray, encounters a TrueHD soundtrack on a disc, it can do several things with it.

The first and most basic thing is to decode it — which in part means unpacking it into multiple channels of uncompressed linear PCM, inside the player. PCM stands for "pulse code modulation," which is a technique for turning an analog waveform into a series of numbers. The amplitude or height of the waveform for each audio channel is, prior to the authoring of the disc, sampled at the rate of, say, 48 or 96 or 192 kHz. 48,000 or 96,000 or 192,000 samples of each waveform's amplitude are accordingly captured every second as numbers expressed in bits: 0's and 1's.

The raw streams of binary numbers are linear PCM: "linear," because the digital streams are not yet encoded and compressed. That happens next, as the multiple raw PCM streams are tamped down by means of the Dolby TrueHD codec into a smaller digital stream to be recorded on disc.

The HD player simply decodes that linear PCM (LPCM) bitstream and unpacks it back into its original multichannel form. The result is absolutely identical to the original, since TrueHD is lossless. Which means, among other things, that if the original had eight (i.e., 7.1) channels, so does the decoded-and-unpacked LPCM. If the original was six-channel (5.1), then so is the decoded-and-unpacked LPCM. And so on.

Downmixing, Downsampling, Downrezzing

The simplest thing that can happen next is what occurs if the TrueHD track is 5.1-channel and the HD player has six standard RCA jacks for routing multichannel analog audio to an A/V receiver. The player simply converts the existing six channels of decoded-and-unpacked linear PCM to analog form and outputs them on the six provided RCA jacks. The receiver inputs the same six analog signals and routes them to the appropriate speakers.

The next most basic option is downmixing the six channels from the TrueHD 5.1 track into two: the traditional stereo right-and-left analog channels. These can then be conveyed to, say, a TV via two standard RCA output jacks on the player, one red and the other white. While the audio is still in its digital linear PCM form inside the player, the information from the to-be-discarded channels is folded into the channels which will remain after the downmixing, so no important sound information disappears.

Downmixing is what happens whenever the number of discrete audio channels is reduced from an original quantity to a lower one. So if the original TrueHD track had 7.1 channels, it's downmixed to 5.1 for the multichannel analog jacks and (again) to 2.0 for the stereo analog jacks.

Thus there can be at least two derivatives of the linear PCM audio present in the player at any moment. As we will be seeing, these or possibly yet other LPCM derivatives can feed the player's digital audio outputs as well.

Some of those digital LPCM derivatives may be downsampled ones. Downsampling involves taking, say, a PCM stream whose sampling rate was originally 96 kHz and reducing it to 48 kHz, by throwing out a fraction (in this case, 50%) of the samples. Downsampling can be useful when the bandwidth of the digital output is less than the original PCM bitrate. It can also be useful if the device doing the processing at the receiving end of the digital connection can't keep up with the original 96 kHz bitrate. Unfortunately, though, downsampling degrades the quality of the sound somewhat.

Another way to economize on bandwidth/bitrate is downrezzing. Downrezzing is slang for "down-resolution," a downscaling process by which the size in bits of each PCM sample is lowered. Say the original samples had 24 bits each. Recomputing them as 16-bit samples saves 1/3 of the digital bandwidth or bitrate. Of course, it noticeably lowers the quality of the sound. For this reason, few if any HD disc players downrez/downscale LPCM.

Players' Digital Audio Outputs

TrueHD can be output by the HD player in various digital forms, using either of two digital connections.

One of these digital connections is usually called something like "digital optical out" or, if it uses a coaxial, non-fiber-optic cable, "digital coaxial out." It's also called Toslink or S/PDIF. I'll just refer to it as "digital audio out," or DAO. The non-optical kind of DAO uses an RCA jack and a coaxial cable much like the type often used for analog video signals. The optical kind uses a fiber-optic cable with special plugs and jacks.

The other digital connection is HDMI, for High-Definition Multimedia Interface. HDMI also carries digital video, along with audio, while DAO does not.

One digital format of TrueHD-derived audio output that can be carried by HDMI and DAO is the above-discussed multichannel linear PCM. It can be output by the player:

  • in its full-fledged player-internal form
  • or as a downmixed and/or downsampled digital derivative

Linear PCM and Bitstream Modes

For each of the two digital audio connections, HDMI and DAO, the HD player typically lets you use one of its setup menus to determine whether or not the uncompressed Linear PCM version (or some derivative thereof) should be output, for decoded audio tracks that were originally encoded in a digital compression codec such as TrueHD. The other menu choice is Bitstream.

When Linear PCM (sometimes just called PCM) is chosen as a player option, the decoded and unpacked audio is routed to HDMI and/or DAO in one of its PCM forms: the original form with all its channels, samples, and bits intact, or a derivative form with fewer channels and/or fewer samples per second.

When Bitstream is chosen, if the original audio track from the disc is TrueHD, then the TrueHD track can be (depending on the player's capabilities — see "Deriving Dolby Digital" below) passed through to the HDMI and/or DAO output jack intact, with no conversion to PCM and no downgrading to a lossy compression codec. The assumption is that the device at the other end of the digital connecting cable — usually an A/V receiver or a TV — knows how to decode TrueHD audio on its own.

In some HD players, the second menu choice for the DAO output is Bitstream while that for the HDMI output is called Auto (not Bitstream). The Auto choice functions pretty much like Bitstream when the HDMI "sink" (usually an A/V receiver) is TrueHD-capable. That is, it sends the original TrueHD bitstream to the sink for decoding.

But when the HDMI sink has no TrueHD decoder, the Auto setting typically reverts to sending multichannel linear PCM to the sink. Virtually all HDMI-equipped receivers can handle that.

Some HD players let you choose among three options for HDMI audio: PCM, Auto, or Bitstream. If you choose Bitstream, you're saying you want a compressed digital bitstream, not uncompressed PCM, always to be sent to the sink.

Deriving Dolby Digital

If that compressed digital output bitstream happened to be in the original TrueHD format, the result might be either no sound at all, or a lot of random noise ... if, that is, the receiver truly has no TrueHD decoder. But HD players that let you choose Bitstream instead of Auto for HDMI often lack the ability to send out on HDMI a TrueHD stream in all its lossless glory, anyway.

What they can have instead is the ability to strip away from TrueHD all the extra bits of information that distinguish such "next-generation" audio streams as Dolby TrueHD from those in the codec's venerable old ancestor format, in this case, Dolby Digital. One player that extracts Dolby Digital 5.1 from Dolby TrueHD bitstreams is Sony's original Blu-ray player, the BDP-S1.

Remember: TrueHD compression is lossless, while DD is lossy. Throw away the extra TrueHD bits that avoid DD's lousiness, and you'll wind up with plain old, lossy DD. So downgrading TrueHD to DD stands to be a relatively simple chore.

In fact — and this factoid is true, as far as I can tell, of Blu-ray players and discs but not of HD DVD players and discs — TrueHD (and Dolby Digital Plus as well) is stored on the Blu-ray disc as two separate components: the independently playable "core" Dolby Digital bitstream, at a bitrate of 640 kilobits per second; and an "extension" bitstream at 1.024 megabits per second. The core bitstream is essentially identical with Dolby Digital 5.1. The extension bitstream is what makes Dolby TrueHD lossless and can also give it extra channels, above and beyond the usual 5.1.

If the TrueHD stream in fact has more than DD's 5.1 channels — say, 7.1 — the extra channels are also carried, in downmixed form, in the core 5.1 bitstream on the Blu-ray disc. They are thus carried separately in the extension bitstream. If the full TrueHD 7.1 audio stream is output on HDMI per the disc player's Bitstream mode, the downmixed "extra copy" of the additional two surround channels being carried in the 5.1 core stream is simply thrown away. If the core 5.1 bitstream is output, the extension bitstream is thrown away.

This would seem to be the strategy used in Blu-ray players, at least. HD DVD discs don't separate TrueHD audio (or DD+, for that matter) into distinct core and extension streams on the disc — one reason being that decoding of DD, DD+, and TrueHD codecs is mandatory for HD DVD players, while only DD decoding is mandatory for Blu-ray, and the ability to decode DD+ and TrueHD is optional. So HD DVD players need to do elaborate tricks in order to extract DD from DD+ or TrueHD for output on DAO or HDMI.

To repeat for clarity's sake: the same thing that happens with TrueHD happens also with Dolby's intermediate-quality format, the lossy-but-not-terribly-so Dolby Digital Plus. On Blu-ray at least, DD+ has a core, DD 5.1-equivalent bitstream alongside an extension bitstream recorded on the disc. So Blu-ray players such as the Sony BDP-S1 that can't output a DD+ bitstream on HDMI downgrade DD+ to DD 5.1 simply by throwing out the extension bitstream. HD DVD players have to do some fancier bitstream manipulations to extract DD from DD+.

What Actually Comes Out, Then?

All the above serves to catalogue some of the kinds of digital audio streams that can come out of a Blu-ray or HD DVD disc player. But what kind of stream actually comes out when a particular TrueHD track is read from a particular Blu-ray or HD DVD disc depends on a few more considerations.

The player's optical or coaxial digital audio output (DAO) has much less bandwidth than HDMI, so the choices there are pretty much limited to a downgraded-to-Dolby Digital 5.1 bitstream or a downmixed 2.o-channel PCM output, depending on whether Bitstream or PCM is chosen in the player's user menu. Moreover, if the TrueHD stream was sampled at 96 kHz or 192 kHz instead of 48 kHz, it's generally downsampled to 48 kHz for DAO, no matter what.

As for the HDMI connection, if it's not implemented as HDMI version 1.3 at both ends, but only as version 1.2 or less, chances are the only improvement over DAO is that the PCM output can be multichannel (up to 5.1 or even 7.1 channels) and not just 2.0-channel.

But if an HDMI connection spans a pair of devices that both implement HDMI version 1.3, there are more possibilities. Of course, HDMI 1.3 (as does every previous version) supports multichannel PCM output, where the maximum total bitrate is 36.86 megabits per second. In PCM mode, that allows for up to eight channels of uncompressed digital audio, each sampled at rates up to 192 kHz, with up to 24 bits per sample.

Now, as of HDMI 1.3, an HDMI source (such as a high-def disc player) in Bitstream mode can export a lossless next-gen digital audio bitstream such as TrueHD as is for decoding by an HDMI sink (such as an A/V receiver or preprocessor).

Because HDMI sources such as disc players and sinks such as receivers compare notes about each other's capabilities before picking the type of audio stream to be transmitted, the actual HDMI 1.3 output of the disc player can depend on the receiver. For example, if the receiver cannot decode TrueHD but can handle Dolby Digital, then TrueHD can in theory be downgraded by the player to DD, which then may be sent across the HDMI 1.3 connection instead.

That being said, chances are that the many HDMI 1.3-capable receivers now just beginning to arrive on the market will all duly decode TrueHD and the other lossless (or lossy) next-gen bitstreams on Blu-ray and HD DVD discs that get passed along to them by HDMI 1.3-enabled disc players in Bitstream output mode.

Alternatively — depending on exactly how digital audio conversion is implemented by the particular model of disc player — TrueHD may be unpacked to multichannel linear PCM and sent to the receiver over HDMI in that uncompressed way ... even though Bitstream has been selected in the player's HDMI setup menu! This is what the Sony PlayStation 3 does when used as a Blu-ray player to play a TrueHD-encoded disc.

Got that? Some high-def disc players may override the Bitstream output mode and substitute PCM output instead, for particular audio compression codecs!

Notice that multichannel linear PCM is compatible with most existing HDMI receivers that don't implement HDMI 1.3, so an HDMI 1.1 or 1.2 A/V receiver usually works just fine with it. (The exception would be some of the cheaper HDMI receivers which do not actually support audio over HDMI and are often labeled as "HDMI passthrough" devices.)

Bitstream Mode and HD DVD "Advanced Content"

There is yet another proviso affecting Bitstream-mode output. It applies to HD DVD players, as distinct from Blu-ray players. Those HD DVD discs that are authored with "advanced content" require audio tracks to be decoded in the player itself.

"Advanced content" uses HDi — see HDi Interactive Format — a disc-authoring option which provides an extra dollop of information on an HD DVD disc which allows the player to do such things as mix the soundtrack of a movie with the director's voiceover commentary and/or provide sound effects keyed to the use of on-screen disc menus. These menus, when invoked, overlay the video of the movie as it continues to play behind the menu on the TV screen.

Mixing multiple video and audio sources in this fashion is one of the ways HD DVD beats regular DVD. For it to work in the HD DVD player's Bitstream mode, the player must internally decode all the audio for all the sources on the disc, mix it together, and output it in one of the player's "blessed" digital audio output formats.

What is a "blessed" format? It is, unsurprisingly, one the HD DVD player uses when the output mode is set to Bitstream in the player's audio setup menu, and the disc being played has been authored with "advanced content."

On current Toshiba HD DVD players, that "blessed" digital audio output format, whether using the HDMI output or the non-HDMI digital audio output connection, tends to be (drum roll, please) DTS 5.1. That's right: even though none of the original audio sources on the disc uses DTS — in any of its versions, DTS, DTS-HD High Resolution or DTS-HD Master Audio — the "advanced content" output on DAO or HDMI can be DTS! Go figure.

Again, what the "blessed" digital audio output format actually is for any current or future HD DVD player, on any particular digital output connection on that player, can vary with the model of player.

Multichannel PCM Mode and "Advanced Content"

When playing "advanced content" with the output mode is set to PCM in the player's audio setup menu, rather than to Bitstream, an HD DVD player will typically play the combined audio as multichannel PCM over HDMI and as downmixed 2.0-channel PCM over DAO.

Virtually all HD DVD discs are authored with "advanced content." The fact that TrueHD and other next-gen audio codecs get turned, by the HD DVD player when in Bitstream mode, into DTS in effect nullifies most of the advantages that typically are thought go along with Bitstream-mode output.

-mode output is generally intended to let an outboard A/V receiver do the heavy lifting of audio decoding, rather than requiring the disc player to be able to do it. For example, many regular DVDs have extra, non-standard audio tracks in formats such as, for example, an enhanced version of the original DTS that carries more than the usual 5.1 channels. If the player can pass such an audio track through to an A/V receiver as an undecoded bitstream, the receiver (assuming it has the proper decoder) can decode it and use it appropriately.

It is accordingly not surprising that some technophiles resent the "advanced content" restriction on Bitstream-mode outputs from HD DVD players. But the (multichannel) PCM output option on HDMI would seem to answer their objections. The player internally decodes TrueHD and unpacks it to into the requisite number of channels of multichannel PCM. Any secondary audio sources are mixed in as needed. The resulting mix is output on HDMI (any version) as is, or it is output on DAO after downmixing to 2.0 channels. The A/V receiver inputs it and makes appropriate use of it.

Notice that the multichannel PCM output on HDMI is just as lossless as the original TrueHD — as long as there has been no internal downsampling or downrezzing of PCM in the disc player.

Notice also that all this works using any HDMI version, with the player's audio mix played into any receiver that can input multichannel PCM on HDMI. The receiver need have no onboard decoder for TrueHD or any other compressed audio formats.

Interactive Content on Blu-ray

The Blu-ray camp doesn't actually use the designation "advanced content" — it was invented by HD DVD bigshot Toshiba to avoid confusing the customer with unfamiliar terms like HDi — but Blu-ray discs can likewise be authored with extra information which allows mixing by the player of multiple audio sources from the disc, and also makes available other ways of using "interactive" audio and video content.

In the case of Blu-ray, the function if HDi in the world of HD DVD is performed by BD-Java. BD-Java, or BD-J for short, stands for Blu-Ray Disc Java, a variation of the Java programming language used widely on the World Wide Web. All Blu-ray players to date support BD-Java.

However, the Blu-ray players that have appeared on the market so far do not yet support the soon-to-arrive bundle of interactive capabilities designated BD-Video 1.1. That "profile" of BD-Video implements basic interactivity features like picture-in-picture, persistent snapshots of video frames, and internal audio mixing. The Blu-ray camp, to speed their format's arrival on the competitive market scene, decided not to require these features on the earliest players. Thus, current Blu-ray players support only BD-Video 1.0.

BD-Video 1.0 as found in today's players does not perform internal mixing of audio. Hence, today's Blu-ray players are fully able to play today's Blu-ray discs, which don't call for internal audio mixing anyway. Some but not all of these early players can provide (if the user prefers) uncompromised Bitstream-mode output of TrueHD, if that is what is on the disc. Others can only extract DD 5.1 bitstreams from TrueHD, when in Bitstream mode. Or, when in PCM mode, uncompressed PCM versions of TrueHD (or of player-extracted DD 5.1) can be output. In none of these cases will internal mixing of audio be necessary.

Eventually, we will see titles on Blu-ray that require internal decoding and mixing of audio by the player, if all the interactive content on the disc is to be used. Players that don't implement BD-Video 1.1 (or its successor profile, BD-Video 2.0, also called BD-Live) will not be able to access this added content, but they will still play the movie itself, with its soundtrack intact.

Again, older players will still (as will the newer, BD-Video 1.1-capable players) allow uncompromised Bitstream-mode output of TrueHD, if that is what is on the disc, and if they have the hardware/firmware to do so (many early players lack that). However, unless the TrueHD from the disc is converted to multichannel PCM inside the player (in PCM mode, not Bitstream), secondary audio sources will not be able to be mixed into it in the final output.

Note, then, the differences between HD DVD advanced content and Blu-ray interactive content. HD DVD advanced content appears on virtually every HD DVD disc and requires player-internal audio mixing in the PCM domain for purposes of PCM audio output on HDMI or optical/coaxial digital connections. Blu-ray interactive content (using the forthcoming BD-Video 1.1 profile) is optional on the disc and can simply be ignored by a non-1.1-compliant player, should it exist on the disc. It can also be ignored by a 1.1-compliant player, if the player is set to Bitstream mode, at the expense of omitting the extra audio information that would otherwise be mixed in from secondary audio sources on the disc.

Viva PCM Mode!

Considering all the above, an interesting notion begins to emerge: It is not clear that using Bitstream mode is ever preferable to using PCM mode on HDMI!

Bitstream mode might (erroneously) be thought to be the only way to get a lossless digital data stream out of the disc player on HDMI when the input to the player from the disc is Dolby TrueHD. TrueHD is inherently lossless, the thinking might go, and exporting it as is to an A/V receiver that can decode it without compromise would seem to be the best way to go.

But the player itself, assuming it can decode TrueHD at all — and, so far, most Blu-ray and all HD DVD players can — does so without compromise. (The Samsung BD-P1000 and BD-P1200 are examples of Blu-ray players that can't decode TrueHD. The BD-P1200 has HDMI 1.3, but lacks TrueHD decoding.) When TrueHD is unpacked to multichannel linear PCM inside the player, it loses nothing: no downmixed audio channels, no tossed-aside digital samples, no discarded bits per sample.

True, when that multichannel PCM is output on a optical/coaxial digital audio connection, it may have to be compromised. To save bandwidth, it may need to be downmixed to 2.0-channel PCM.

When it is output on HDMI, though, the player's internal multichannel PCM should in no way have to be downconverted — downmixed, downsampled, or downrezzed — with the following exceptions:

  • TrueHD sampled at 192 kHz may get downmixed to 2.0-channel PCM (some early players seem to do this, even though it's not clear why)
  • Some of the very first HD DVD and Blu-ray players originally downmixed all TrueHD to 2.0-channel PCM; that limitation has been corrected by firmware updates and in follow-on models
  • Some HDMI-passthrough A/V receivers are not compatible with digital audio input at all
Notice that no exception need be made when the HDMI version in use is earlier than 1.3. By way of comparison, TrueHD cannot be output in Bitstream mode unless the HDMI version is (at least) 1.3.

What's more, TrueHD cannot be output in Bitstream mode unless a disc player that implements HDMI 1.3 also contains the necessary hardware chipsets and/or firmware smarts to pass along TrueHD bitstreams on HDMI. It is admittedly not easy to find out which HDMI 1.3 players, if any, have or lack this capability. But the question becomes moot if PCM mode is selected instead of Bitstream, anyway.

And so it looks as if setting the player to use PCM output mode on HDMI is just about always the right way to go. On HDMI, multichannel PCM covers all bases in terms of losslessness and the number of channels supported.

On coaxial/optical digital audio outputs, on the other hand, Bitstream mode is useful as the only way to convert TrueHD into a multichannel codec — Dolby Digital 5.1 or DTS 5.1 — that uses less bandwidth and can accordingly work. If PCM mode is selected for DAO, the result will be only 2.0-channel linear PCM. The surround sound capabilities of TrueHD will be lost.

Saturday, July 21, 2007

Blu-Ray and HD DVD Players and Prices (as of 7/21/07)

One of the easier ways to get a quick rundown on what Blu-ray and HD DVD players cost today is to visit this page at

Blu-ray and HD DVD are, of course, the two competing formats for high-definition video discs, one or both of which may someday supplant the familiar, not-so-high-def DVD.

Blu-ray discs (aka BD-ROMs) can't be played in HD DVD players, and HD DVDs don't work in Blu-ray players. Both hi-def formats' players usually accept regular DVDs as well (but some won't play CDs). There is at least one player which plays BD-ROMs, HD DVDs, and DVDs: the BH100 from LG Electronics.

HD DVD Players

According to PriceGrabber, Toshiba sells six HD DVD players:

  • HD-A1 - low price, new: $319
  • HD-D1 - low price, new: $324
  • HD-A2 - low price, new: $235
  • HD-A20 - low price, new: $318
  • HD-XA1 - low price, new: $394
  • HD-XA2 - low price, new: $595

The HD-A1 and HD-XA1 are no longer made. (Here and often in what follows, clicking on the model number takes you to a CNET review.) The HD-D1 was sold by WalMart and was essentially the same as the HD-A1, with minor cosmetic differences. These models are already obsolete, with performance and reliability issues that have largely been fixed in their follow-ons.

The HD-A2 and HD-XA2 are the respective second-generation, follow-on players to the HD-A1 and the HD-XA1. (There is also an HD-D2, the WalMart version of the HD-A2.) The HD-XA2 is Toshiba's current flagship HD DVD player, with nice features like HDMI 1.3 and 1080p output. HDMI 1.3 supports so-called Deep Color technology, meaning that each of the three primary video colors (red, green, and blue) are carried at 10 bits per color, not 8 bits. So if the HD-XA2 is used with a TV that also supports Deep Color/10-bit technology, the result can be subtler color gradations with no color "banding" apparent on the screen.

The HD-A2 only supports HDMI 1.2, with no Deep Color, and 1080i (though the HD-A20 adds 1080p; see below). The HD-A2 also lacks the 6-channel analog audio outputs of the HD-XA2 and many other high-def disc players.

The HD-A20 is basically the HD-A2 with 1080p output added (but not HDMI 1.3/Deep Color).

There is a single HD DVD player available from RCA. The RCA HDV-5000 (aka HSDV5000?) is, or was, the Toshiba HD-A1 rebranded by RCA.

Sony Blu-ray Players

While Toshiba was the original proponent of HD DVD players, Sony made the first announced Blu-ray players. PriceGrabber shows Sony has produced two models to date:

  • BDP-S1 - low price, new: $609
  • BDP-S300 - low price, new: $475

The BDP-S1 was Sony's original Blu-ray player. When it came out last year, it was the only player in either hi-def camp to output true 1080p. Since then the HD DVD camp has remedied that oversight, and it's hard to find a good reason to buy the relatively pricey BDP-S1 today.

To help narrow HD DVD players' significant price advantage, Sony recently came out with the BDP-S300 "budget" model. It can't decode high-resolution, lossless soundtrack formats like Dolby TrueHD or DTS-HD Master Audio. (The BDP-S1 apparently can decode Dolby TrueHD, with Sony's latest firmware update.)

Sony's PlayStation 3

Sony also makes the PlayStation 3 high-def video gaming console, which doubles as a standalone Blu-ray player. Its low price, in new condition, is currently $456, making it for many buyers an even better deal than the BDP-S300.

The PS3 produces 1080p video and utilizes HDMI 1.3. It apparently can pass next-gen surround-sound audio such as Dolby Digital Plus and Dolby TrueHD to compatible A/V receivers via an HDMI cable.

The PS3 is unlike "real" standalone Blu-ray players in that it does not offer analog output connections, either multichannel or two-channel stereo. It outputs digital audio only, on any of three connectors: HDMI, optical, or SCART/AV MULTI. (The last is for European users.)

What form the PS3's digital audio output takes depends on the form of the digital audio track on the disc being played, on which digital audio connection is being used, and on selections made in the user menus. In general, the PS3 will output recognized audio codecs in one of two forms, linear PCM or bitstream. (See this PC World article for more on this and other aspects of using the PS3 as a standalone movie player.)

I'll go into more detail on the subject of digital audio output and the PS3 because what the PS3 does with digital audio output is much like what any other Blu-ray or HD DVD player can be expected to do.

• With bitstream output selected in the PS3, the audio bitstream from the disc will appear — as is, or in only slightly modified form — at the player's HDMI or optical digital output, whether that audio bitstream is linear PCM, Dolby Digital, Dolby Digital Plus, Dolby TrueHD, DTS, or DTS-HD. The receiving component, usually an A/V receiver, is then expected to decode and use the digital audio.

Bitstream output mode is not a simple pass-along of the audio track exactly as it is found on the disc. DTS-HD with 7.1 channels is output by the PS3 on HDMI with only 5.1 channels, for example. Presumably the extra two channels are downmixed into the 5.1-channel output.

This confirms that bitstream output mode on the PS3, and presumably on other high-def players as well, requires the player to be able to read and decode the bitstream on the disc — not just blindly pass it through.

For an example of another player's bitstream output logic, the Sony BDP-S1 apparently demotes Dolby Digital Plus 5.1 audio to Dolby Digital 5.1 (tossing aside the extra data required for the "Plus" designation). In similar fashion, the BDP-S1 outputs DTS-HD, in bitstream output mode, as plain old "core" DTS.

It's not clear whether both DTS-HD formats, "High Resolution" and "Master Audio," qualify for bitstream output on the PS3. "Master Audio" bitstream output is definitely supported — it's the more data-intensive of the two DTS-HD formats, since it's compression is totally lossless. If MA can be output as a bitstream from the PS3, presumably HR can, too.

Nor is it clear whether bitstreams whose bitrate in bits per second are very high can be successfully passed to the PS3's optical digital output, specifically, which is slower than HDMI.

The SCART/AV MULTI connection on the PS3 is apparently ineligible for bitstream output entirely. It can output only 2.0-channel linear PCM.

• With linear PCM output selected, the PS3 will convert the audio track (unless it's already PCM) to multichannel linear PCM. It may downmix 7.1 audio channels, if present, to 5.1 channels, or it may downmix 7.1-channel or 5.1-channel multichannel audio all the way down to 2.0-channel stereo — it all depends on your connection type and on other variables.

  • 7.1 digital audio output channels of linear PCM is possible only with an HDMI connection, and then only when the receiving device can handle 7.1-channel LPCM input. Also, DTS-HD 7.1 audio tracks (whether lossless "Master Audio" or merely lossy "High Resolution," I presume) are always downmixed to 5.1 when converted by the PS3 to LPCM.
  • 5.1 digital audio output channels of linear PCM can be output on an HDMI connection, in linear PCM mode, just about anytime there is a multichannel audio track being played on the disc. The same is true for the PS3's optical digital out connector. Dolby Digital, Dolby Digital Plus, Dolby TrueHD, DTS, or DTS-HD — all these compressed codecs can be transcoded to uncompressed 5.1-channel LPCM by the PS3.
  • 2.0 digital audio channels of linear PCM can always be chosen for output on the HDMI connection, the optical digital out connection, or the SCART/AV MULTI connection, for receiving devices (particularly TVs) that can't use the extra channels.
  • Anytime the output linear PCM has fewer channels than the input audio track originally had, it is downmixed by the PS3 to the requisite number of channels. The extra channels are never just "thrown away."

The basic purpose of the linear PCM output mode would accordingly seem to be to force the PS3 to provide its digital audio output in a form that any receiver or TV can handle — i.e., PCM — rather than require the receiver or TV to decode Dolby- or DTS-compressed audio. Linear PCM output is the default choice on the PS3, if the user doesn't manually change the output to bitstream.

The PS3 originally did not upscale standard DVDs to HD resolutions, a feature that's standard on other Blu-ray and HD-DVD players, including Sony's BDP-S300. Instead, they default to 480p. But if the TV to which the PS3 is connected scales 480p to (say) 1080p nicely enough, that wouldn't be a problem.

(Note: since this report was first posted, it has received a comment from Kari, who says the PS3's latest firmware upgrade — system software update 1.82 — allows it to upscale regular DVDs after all.)

Other Blu-ray Players

Samsung was the second kid on the block with Blu-ray players. Their models include:

  • BD-P1000 - low price, new: $489
  • BD-P1200 - low price, new: $485

The BD-P1000 was actually the first Blu-ray player to become available, owing to delays in the arrival of the much-publicized Sony BDP-S1, which had originally been expected to ship before the Samsung player. It's now obsolete.

The BD-P1200 is Samsung's second-generation follow-on to the BDP-1000. Unlike its predecessor, the BDP-1200 can play audio CDs, and has an HDMI 1.3 port for Deep Color support and also for compatibility with the new high-bitrate audio codecs. Yet (as was also true with the BDP-1000) it can't decode Dolby TrueHD or DTS HD-Master, the two new lossless sound codecs. Even Toshiba's entry-level HD-A2, in the HD DVD camp, can handle Dolby TrueHD.

The BD-P1200 is one of the second-generation Blu-Ray players, however, that can output 1080p at 24 frames per second (24 fps), just as recorded on Blu-ray movie discs. That mode, which is sometimes called Source Direct, obviates an unnecessary conversion to 60 fps, which can introduce visible artifacts on the TV screen. But the TV at the other end of the HDMI cable has to be able to accept 1080p/24 input, or 1080p/60 output conversion must indeed be chosen in the player instead.

Another big-name maker of Blu-ray players is Panasonic. Its models include:

  • DMP-BD10 - low price, new: $599
  • DMP-BD10A - low price, new: $598

The DMP-BD10 was Panasonic's original Blu-ray player.

The DMP-BD10A (aka DMP-BD10AK?) is basically the same unit with a lower suggested price and with five free Blu-ray movies bundled with it. It features 1080p video output and decodes Dolby TrueHD and DTS-HD High Resolution audio. The former is a lossless multichannel codec, the latter lossy; DTS-HD Master Audio, which is lossless, is not supported.

Philips makes one Blu-ray player:

  • BDP9000 - low price, new: $709

The BDP9000 outputs 1080p video but does not pass through or internally decode either of the two major new multichannel audio codecs, Dolby TrueHD and DTS-HD (in either its lossy High Definition or its lossless Master Audio form). It does pass through (but not decode) lossy Dolby Digital Plus, also a new codec, and it decodes familiar Dolby Digital (without the Plus) and DTS (without the HD).

Pioneer's Blu-ray player, the Pioneer Elite BDP-HD1, doesn't show up in PriceGrabber. It doesn't seem to be widely available online. There are a few sources that turn up in a Google Products search, however, and Google shows the unit's low price to be about $900.

The BDP-HD1 supports 1080p video output, but lacks HDMI 1.3 and cannot play audio CDs. Its ability to upconvert DVD video to simulate high-def quality is not as good as some other players'. It supports 1080p/24 output as well as 1080p/60.

"Combo" Players

Only one player exists which can play both HD DVDs and Blu-ray discs. It is from LG Electronics:

  • BH100 - low price, new: $799.

The BH100 is, as I say, the only "combo" high-def player currently marketed. But it won't play CDs. Nor is it a fully compliant HD DVD player, since it does not support HDi interactive features: technology that enables features such as customized menus and picture-in-picture video commentary over a movie. That means you're stuck with a bare-bones user interface on HD DVDs.

The BH100 also has significant audio limitations. Per CNET, "DTS-HD and Dolby Digital Plus are dialed down just standard DTS and Dolby Digital when output over the HDMI connection. If uncompressed linear PCM is encoded on the disc, output over HDMI is limited to two channels. And although you can get five channel DTS-HD, Dolby Digital Plus, and linear PCM to pass via the BH100's analog multichannel outputs, they cannot pass Dolby TrueHD in surround sound at all — all Dolby TrueHD soundtracks are output in stereo over analog and digital connections."

Furthermore, the BH100 lacks HDMI version 1.3, and the 1080p video output it is capable of delivering is locked in at a 24-fps frame rate. No 1080p/60 option is present, meaning the TV will have to accept 1080p/24 — and few TVs that input 1080p at all do it at 24 fps yet. Otherwise, high-def BH100 video output must be restricted to 1080i or 720p.

It is perhaps worth noting that you could buy a Sony PlayStation 3 for roughly $470 and a Toshiba HD-A20 for roughly $330, for a total outlay of about $800 — the street price of LG Electronics' BH100 "combo" player. You would then have the ability to play Blu-ray discs and HD DVDs at 1080p/60 resolution, as well as the ability to upscale regular DVDs and to play audio CDs. You could also play PS3 games, which the BH100 won't do. Nor would HD DVD playback be crippled by a lack of support for HDi interactive features.

True, you would be missing HDMI 1.3 support on the HD DVD player, with its ability to utilize Deep Color technology and pass along all the latest audio codecs and/or transmit maximum-definition multichannel PCM. (The PS3 supports HDMI 1.3.) But the BH100 lacks HDMI 1.3 as well, and furthermore won't decode multichannel Dolby TrueHD as anything but two-channel stereo.

It is also true that neither member of the PS3/HD-A20 tandem supports 1080p output at the film-native frame rate of 24 fps. If your TV supports 1080p/24 input, the BH100 might be a better deal for you. But most TVs today don't accept 1080p/24 — just 1080p/60.

It accordingly seems to this observer as if "combo" high-def players like the BH100 aren't quite ready for prime time yet.

Buying Strategy

All in all, it looks as if the smartest thing to do, if you want to buy a high-def disc player, is wait.

According to this considered opinion by the folks who create the TheDigitalBits website, HD DVD is apt to start playing second fiddle to Blu-ray in terms of industry support and consumer acceptance over the next year or less.

Already, there is only one major movie studio not releasing on Blu-ray: Universal alone is HD-pure. Meanwhile, Blu-ray has five exclusive studios: Disney, Fox, MGM, Lionsgate and Sony. Three remaining majors — Warner, Paramount, and DreamWorks — support both formats, and New Line has indicated it will likely do the same. TheDigitalBits thinks Universal will cave and go "format neutral" — i.e., release discs in both Blu-Ray and HD DVD — by next January at the latest.

As of right now, HD-DVD has 207 titles released, plus 54 more announced. Blu-ray has 241 titles released, with 40 more announced.

Sony's Blu-ray players could drop to as low as $299 by the holidays this year, according to this online story. Pioneer, Panasonic, Philips and Samsung say they will have cheaper players available by the end of the year as well, some of them in the $399 price range.

That's not as cheap as some HD DVD players already go for, as noted above ... apparently because Toshiba is selling players at a loss to lock in consumer support for its pet disc format, since it gets royalties on every disc sold. That keeps other manufacturers, who get no royalties, from joining the HD DVD bandwagon; they just aren't interested in negative profits. But Toshiba can't eat losses on player sales forever.

TheDigitalBits thinks Microsoft may be subsidizing those losses because it (temporarily) favors HD DVD over Blu-ray. After all, HD DVD discs typically use Microsoft's VC-1 video compression codec, putting money in Microsoft's coffers. (Blu-ray discs increasingly use the same codec, however.) Microsoft's Xbox 360 video gaming console has an HD DVD option, but not one for Blu-ray — but one for Blu-ray could easily become a future add-on.

But Microsoft ultimately wants to kayo disc-based home video entirely, in favor of online downloads à la Xbox Live. TheDigitalBits says:

Microsoft doesn't give a rip about HD-DVD, or movies on disc at all for that matter, except to the extent that backing HD-DVD for a while now both undermines Sony's efforts and leverages Microsoft's success in achieving their ultimate goal of dominating the future of online distribution of digital entertainment. And hey... if fueling a format war in the meantime creates consumer confusion that hastens the demise of discs and the advent of mainstream downloading, so much the better for Microsoft. That's how we see it.

TheDigitalBits thinks Blu-ray will triumph anyway, Microsoft be damned. HD DVD may hang on for quite some time as a second consumer format, the way Sony's own Betamax did even after VHS had come to dominate the VCR market. But it looks like consumers no longer need to fear adopting Blu-ray, if they so desire.

Still, I think it best to wait until lower-priced, fuller-featured Blu-ray players appear, before I buy. In addition to being more affordable, they're likely to support 1080p output at 24 fps or 60 fps, at the user's option; HDMI 1.3 with Deep Color and full support for advanced multichannel audio codecs; internal decoding (and also pass-along) of lossless audio codecs such as Dolby TrueHD and DTS-HD Master Audio, with no quality compromises; audio CD play; and uniformly excellent upscaling of regular DVDs to 1080p.

Another reason to wait to buy Blu-ray is that current players support only a crippled, introductory version of Blu-ray's slated repertoire of interactive audio and video capabilities. These extra capabilities above and beyond the standard ability to just play a movie are lumped together under the designation BD-Video.

The version of BD-Video in current Blu-ray players, profile 1.0, lacks the ability to play the various interactive features of Blu-ray discs that are said to be coming in the near future: picture-in-picture filmmakers' commentaries, secondary audio mixing of voiceover commentaries with movie soundtracks, and persistent snapshots of video frames to be stored in flash memory.

BD-Video profile 1.1 is due to arrive in player models introduced after the end of October 2007, along with new disc releases that have interactive features.

Theoretically, profile-1.0 players could gain some of profile 1.1's interactive ability with firmware updates alone, but without the necessary extra memory and other hardware upgrades, their compatibility with BD-Video/BD-Live would be limited at best.

Another future version of Blu-ray interactivity is called BD-Live. Also called BD-Video profile 2.0, it adds yet more memory and the ability for the player to go online to the Internet to get extra content to go with what's already on the disc. With BD-Live content implemented, movie studios can incorporate the capabilities to download new trailers, additional behind the scenes footage or even a whole website that can be pulled up when you insert the disc in the player. There is no firm date for BD-Live's arrival in Blu-ray players.

BD-Java (a.k.a. BD-J) is a computer language that is built into all Blu-ray players, even current models. Future BD-J "extras" will allow players yet to come to play all of that profile 1.1/2.0 interactive content ... given that the necessary BD-Video/BD-Live profile is also fully implemented in the player's hardware and firmware.

The HD DVD camp has had what it calls "advanced content" — its implementation of interactive disc content — right from the start. HD DVD interactivity uses the HDi Interactive Format. This area of disc interactivity is clearly one in which Blu-ray is playing catchup.

Friday, July 13, 2007

In Praise of HDMI

As I said in Aiming Towards a New Living Room TV, I am planning to connect a TiVo Series3 digital video recorder to a 46" flat-panel HDTV from Sony, possibly the model KDL-46XBR2, XBR3, or XBR4. I'll also incorporate a Blu-ray high-def disc player or HD DVD player into the system at some future point. All of the interconnection of components will be via HDMI.

High-Definition Multimedia Interface offers a single-cable connection that carries both video and audio signals. The "HDMI source" can be, say, a DVD player or a DVR. The "HDMI receiver" can be, for example, an HDTV or an audio/video receiver. And the HDMI receiver can send its input HDMI signals on to yet another device. For example, a DVD player can output HDMI signals directly to an A/V receiver, which passes them along to an HDTV. Yet more complex HDMI interconnections use repeaters, distribution amplifiers, and/or switches.

HDMI carries only digital (not analog) signals: high-def video in all available compressed and uncompressed formats; compressed and uncompressed audio in numerous codecs, including the new "lossless" ones on Blu-ray discs and HD DVDs; and other information that allows pressing one button on a remote to control multiple components. This feature is sometimes called "one-touch play," because pressing PLAY on the remote can turn on the TV set and the A/V receiver, select the right inputs on each, and begin playing a DVD.

One of the best things about HDMI is that it eliminates "cable clutter" by becoming the sole cable between any pair of components.

Because HDMI uses two-way communication between source and receiver, a system using HDMI interconnections can automatically configure itself. HDMI devices automatically work together to deliver the most effective video format (480p vs. 720p vs. 1080i/p, 16:9 vs. 4:3) for the source device and the display that it is connected to — eliminating the need for the user to scroll through all the format options on each device to guess what looks best.

The same is true for audio. A source device such as a DVR and an A/V receiver can negotiate to use (say) either Dolby Digital or 2.0-channel linear PCM, depending on the capabilities of each device, and on the nature of the program material.

For example, I now have a Sony KDL-40XBR2 flat-panel HDTV in my bedroom, fed both its audio and its video by a TiVo Series3 DVR, via HDMI. The TiVo is connected to a Comcast cable feed as its input, and uses two CableCARDs to authorize access to the channels I subscribe to. Some of these channels are the old analog kind; their audio is likewise analog. Some channels/programs are digital but lack Dolby Digital 5.1 audio, while other digital channels/programs do have DD 5.1 multichannel audio.

As far as I can tell from the Sony literature, the only type of digital audio the TV can decode is 2.0-channel PCM. It can't handle DD 5.1.

No matter what kind of audio is on the program I am watching, though, it plays fine through the TV.

That means the TiVo must be transcoding the DD 5.1 soundtracks it receives into 2.0-channel PCM. (PCM stands for "pulse code modulation," which is how "linear" or uncompressed digital audio is carried.)

Interestingly, in one of the TiVo's settings menus there is an option that tells the TiVo to transcode Dolby Digital to PCM. In my system, it's unnecessary. Even when it's not enabled, the digital audio sent to the TV gets transcoded anyway!

Why? Because the HDMI two-way interconnection is smart. In effect, the TiVo tells the TV, "Hey, I have a Dolby Digital 5.1 soundtrack I want to send you. Can you handle it?" The TV answers back, "No can do. I can only use 2.0-channel linear PCM." So the TiVo says, "Fine with me, I'll just transcode it so you can deal with it."

However, I cannot tell that my TiVo and TV coordinate video options like aspect ratio and resolution in any way. Pending further research, my assumption is that not all HDMI devices yet take advantage of all the possibilities HDMI offers.

Anyone interested in learning more about HDMI can visit I encourage you to take their quick, 30-minute audio-visual tutorial here.

Sunday, July 08, 2007

Future-Proof Home Theater Audio

As I mentioned in Aiming Towards a New Living Room TV, I'm contemplating a new living room home theater, minimalist-style. That means I'll eschew having multichannel sound. The audio channels from my TiVo Series3 DVR and from the high-def disc player I'll eventually get will pass to the TV and its internal speakers, for now.

That does not, however, mean I won't someday add in a home theater audio system. Which means I need to bear in mind what the future of home theater audio will be.

That future is spelled out in the standards for the two competing high-def disc formats, HD DVD and Blu-ray, as complemented by the new HDMI 1.3 standard for routing digital audio/video signals from source equipment like disc players to receiving equipment like HDTVs and A/V receivers.

In what follows, I'm going to abbreviate "high-definition disc formats" as HDDFs.

The two HDDFs, HD DVD and Blu-ray, are alike in that they both support a multiplicity of audio codecs. A codec is basically a digital encoding-decoding format for, in this case, digital audio. There are also a number of codecs for digital video.

Each disc, in either of the HDDFs or as a "regular" DVD, contains at least one — and often several — digital audio streams; for instance, a movie's soundtrack in a given codec will constitute one stream. On a regular, non-high definition DVD, the soundtrack will usually be encoded as Dolby Digital 5.1. That means there are five digital audio channels, plus one (the ".1") containing "low frequency effects" only in the bass range. The five full-frequency channels are front-left, front-center, front-right, and two side/rear "surround sound" channels.

Somewhere along the line, DD 5.1 acquired the alternate name "AC-3." But never mind ... by whatever name, the "encoding side" of the DD 5.1 or AC-3 codec is used to define the stream of computer bits and bytes to be recorded on the disc. Then, as the disc player reads the disc, the codec's "decoding side" separates out the 5.1 channels and, if you don't have a multichannel home theater setup, mixes them into two stereo analog (i.e., non-digital) channels for output to a TV that cannot decode DD 5.1.

If you have a multichannel home theater setup, the disc player can output fully six channels (including the ".1" LFE channel) of analog audio to it. Or, it can delegate the "decoding side" responsibility to the multichannel home theater receiver. In that case, the original DD 5.1 audio stream, read straight from the disc, is sent directly to the receiver for decoding. Nowadays, an HDMI connection between the player and the receiver typically carries the output DD 5.1 bitstream.

What happens when there's no DD 5.1 stream on the DVD? Actually, that almost never happens, since DD 5.1 is one of two codecs that every DVD made for sale in the United States has to support at least one of. The other is so-called linear PCM, where PCM stands for pulse code modulation.

Historically, linear PCM audio streams were typically stereo, not multichannel; they are what have long been used on CDs. They were (and remain) digital, not analog. As "linear" digital encodings, they are, unlike DD 5.1, not digitally compressed ... so encoding and decoding them is a snap. Because they are uncompressed, they are "lossless." Where "lossy" compression codecs like DD 5.1 discard audio information which hopefully your ears will never miss, lossless encoding sidesteps the risk of over-enthusiastic compression entirely.

But they use up a lot more of the available bits on the DVD. You'll find few DVDs with linear PCM tracks for that reason.

Actually, I need to slightly qualify the idea that linear PCM is always lossless. If the original recording from which the linear PCM track on a disc is derived has a higher sampling frequency or greater bit depth, the track on the disc has less resolution than the original.

Linear PCM encoding involves treating each sound channel as a rising and falling electronic waveform whose amplitude is sampled several thousand times per second — the sampling frequency. Each amplitude is expressed as a binary number requiring a certain number of 0's and 1's — the bit depth or sample resolution.

Sampling rate or frequency for CDs is usually 44.1 kilohertz (thousands of samples per second). For DVDs and HDDFs, it can be 48 kHz, 96 kHz, or 192 kHz.

Sampling resolution — bit depth — is typically 16, 24, or 32 bits per sample, although other resolutions are sometimes used. Accordingly, the overall resolution of a linear PCM track can be stated briefly. For example, you may find 48 kHz/16-bit resolution (which is typical on DVDs) or 96 kHz/24-bit (common in HDDFs).

But if the overall resolution of the source soundtrack exceeds that of the disc track in either of its two key parameters, the linear PCM disc track has in effect been compressed, and cannot really be called lossless.

Likewise, if there is a 96 kHz/24-bit linear PCM track on the disc but the player downsamples it to 48 kHz/16-bit, a lossy compression has in effect been done within the player itself.

So ... most regular DVDs have DD 5.1 tracks, but few have linear PCM at all. Many DVDs supplement their DD 5.1 tracks, however, with tracks encoded using an optional audio codec called Digital Theater System, or DTS. DTS is, like DD 5.1, a 5.1-channel surround sound format. If there's a DTS track on a particular DVD, it will be selectable via a menu in lieu of the standard DD 5.1 track. Many DVD players can decode DTS internally. Virtually all can export it as-is to an external receiver for decoding.

Again, that is typically done today via an HDMI digital audio/video connection — a single cable that carries both digital audio and digital video. The receiver is typically responsible for grabbing the digital audio for its own internal use, while forwarding the digital video stream to the TV.

Older equipment did it a different way. The digital video stream was sent directly from the disc player to the TV via an HDMI cable or its now-obsolete predecessor, DVI. (DVI used a different kind of plug at each end of its cable and could not carry audio information.) Meanwhile, the digital audio stream was routed to the A/V receiver via a dedicated digital-audio conduit, which could be either "optical" or "coaxial."

All of which points up a general principle: whatever digital-audio codecs are present on a DVD or an HDDF (HD DVD or Blu-ray disc) need to have one of two things happen to them:

  1. The one that is automatically chosen by the player, or that is optionally selected by the user, has to be decoded internally by the player, or,
  2. The one that is automatically chosen by the player, or that is optionally selected by the user, has to be routed as-is to external equipment for decoding.

Actually, there is a third possibility. (I never told you this couldn't get confusing.) The player can "transcode" the digital audio from the disc, converting it into a different codec or format. That almost never happens with regular DVDs played by regular DVD players, but with the new HDDFs it tends to happen more often.

For instance, Blu-ray and HD DVD each support, at least optionally, certain new audio codecs that offer superior sound to DD 5.1, DTS, or even 2.0-channel linear PCM.

I'll use the new Dolby TrueHD codec as an example. Dolby TrueHD, like DD 5.1, was developed by Dolby Laboratories. Like DD 5.1, it's compressed, not linear. But unlike DD 5.1, the compression scheme is lossless. Accordingly, the result can be noticeably better sound.

Dolby TrueHD can contain many more sound channels than the 5.1 of Dolby Digital — up to 14! The Blu-ray and HD DVD standards allow up to 8 of the 14 to be used on a disc, in up to a "7.1" configuration where the ".1" again refers to the LFE, bass-only channel. Or, more commonly today, TrueHD 5.1 can be encoded on the disc.

But HD DVD players are allowed to "downmix" those 5.1 or 7.1 channels into just two stereo channels. For example, if there is a TrueHD 5.1 audio track on a disc, the player is not absolutely required to output it as such. Instead, the player can transcode it into TrueHD 2.0. (In fact, I am given to understand that no current HD DVD players actually do downmix TrueHD 5.1 to TrueHD 2.0, but it is legal.)

As for Blu-ray players, they don't necessarily even have to recognize Dolby TrueHD tracks, however many or few the number of channels contained therein. Dolby TrueHD tracks are strictly optional on BD-ROMs, the official name of Blu-ray discs. Dolby TrueHD is a mandatory codec on HD DVDs; all discs must use it, and all players must output it, if only in downmixed form.

Again, to repeat, Dolby TrueHD is an optional codec on BD-ROMs, and not all Blu-ray players have to be able to deal with it at all.

Another transcoding option legally utilized by Blu-ray and HD DVD players is to decode, say, Dolby TrueHD into multichannel linear PCM. Instead of sending out just 2.0-channel, stereo LPCM, all 5.1 or 7.1 channels encoded as Dolby TrueHD on a disc are decoded inside the player and shipped out to an external receiver in an uncompressed digital-audio stream having an equal number of channels ... again via HDMI.

Multichannel LPCM involves a huge bitrate. The "bitrate" measures how many bits per second have to pass from the player to the receiver. Because the bitrate is so high with multichannel LPCM, a new HDMI standard — called "version 1.3" — needs to be supported by both the player and the receiver ... either that, or the multichannel LPCM bitrate has to be curtailed, by downsampling, to fit within the limit supported by HDMI 1.2.

Downsampling, as mentioned earlier, involves lowering the bit depth of the linear PCM samples from, say, 24 bits to 16 bits. Or it can involve changing the sampling frequency from, say, 24 kHz to 16 kHz.

Downsampling causes a loss in audio quality. In future-proofing a home theater audio system today, one should buy nothing but HDMI 1.3-compatible gear that is comfy with high-bitrate, multichannel LPCM.

The reason why will become apparent when you consider the three other new audio codecs you're apt to run into on Blu-ray or HD DVD discs: Dolby Digital Plus, DTS-HD High Resolution, and DTS-HD Master Audio.

Before I discuss each of them, I'd like to point out some general things about them:

  • Some of them are "mandatory"; the rest are only "optional"
  • Which ones are "mandatory" depends on the disc format, HD DVD or Blu-ray
  • A format's "mandatory" codecs must be supported by every player for that format
  • Each disc must use one or more of the format's "mandatory" codecs

For example, the new Dolby Digital Plus (DD+) codec is mandatory for HD DVD but only optional for Blu-ray.

So every HD DVD player must be able to "use" a DD+ audio track if there's one recorded on the disc — provided, that is, that the track's bitrate does not exceed 1.7 million bits per second (1.7 Mbps). (The bitrate of a digital audio track tells the maximum number of bits per second the player is expected to be able to accept and decode.)

Here, "use" apparently means having the ability to, at minimum, extract and decode a 2.o-channel analog stereo waveform from a TrueHD bitstream. That waveform can drive the analog stereo audio outputs of the player. Or it can be re-encoded as 2.0-channel LPCM and delegated to an outboard receiver for decoding and use.

So, if more than two channels — up to 7.1 — happen to be present in a DD+ audio track on HD DVD, it can legally be "downmixed" (transcoded) by the player into just 2.0-channel form. That qualifies as "using" the track.

Of course, most or all real-world HD DVD players can do more than that with Dolby Digital Plus bitstreams. Many of the HD DVD players can pass the Dolby Digital Plus bitstreams through, undecoded, to an external receiver which will decode and use them to drive speakers.

Many of the players can also "unpack" (transcode) Dolby Digital Plus bitstreams to multichannel linear PCM to be sent to an outboard receiver via HDMI 1.3. That's why I said above that in future-proofing a home theater audio system today, one should buy nothing but HDMI 1.3-compatible gear that is onboard with high-bitrate, multichannel LPCM.

Finally, yet another way for the player to "use" a Dolby Digital Plus bitstream is to convert it to (up to) six analog channels to be output on a group of six RCA jacks included on the player. There can be three front channels, two surround channels, and one LFE channel output in analog form by these six multichannel audio jacks. A Dolby Digital Plus bitstream can be decoded and used to feed those jacks, which in turn feed an A/V receiver with suitable 6-channel inputs.

The six analog jacks in question are separate from the two analog jacks on the player that carry only downmixed 2.0-channel stereo. However, it stands to reason that most players that "use" a Dolby Digital Plus bitstream to drive their six multichannel analog outputs will also downmix the bitstream for their two analog stereo output jacks.

Accordingly, these are the various things a given high-def disc player may be able to do with any given audio bitstream on a disc it is playing, whether the bitstream is Dolby Digital Plus or otherwise:

  • Ignore it (not allowed if the bitstream's codec is "mandatory" for the disc format)
  • Pass it through undecoded to external gear
  • Transcode it to, say, multichannel linear PCM and route it to external gear that way
  • Use it to drive the player's own 2.0-channel and/or 5.1-channel analog audio output jacks (required if the bitstream's codec is "mandatory" for the disc format)

What a Blu-ray player does with Dolby Digital Plus bitstreams, should any be present on a disc, is equally free-form. The player can simply ignore the bitstream, since DD+ is "optional" for Blu-ray. The player can pass the original digital bitstream as-is to outboard gear for decoding and handling. The player can unpack it to multichannel linear PCM for digital output. Or the player can convert it for analog multichannel output and/or downmix it for analog stereo output.

The straight pass-through option means the external gear has to be able to decode Dolby Digital Plus bitstreams, of course. When you widen that scenario to include the other two codecs I've yet to discuss, DTS-HD High Resolution and DTS-HD Master Audio, you can see that today's A/V receivers need to incorporate a lot of codecs to be absolutely future-proof.

Alternatively, a receiver that handles any variety of multichannel linear PCM the disc player throws its way covers all bases — provided the disc player can transcode to multichannel linear PCM any audio track on any disc it can play, without compromising the overall resolution of the original audio track in terms of its bit depth and sampling frequency.

(I'm getting tired of repeating "multichannel linear PCM" ... from now on, it's MLPCM.)

MLPCM can be thought of as an umbrella codec that can take the transcoded digital audio from any original codec on any disc and render it usable by the receiver. (Again, there may be issues of downsampling to a lower overall resolution than that of the original audio stream.)

DTS-HD High Resolution and DTS-HD Master Audio are two new codecs from the folks who brought you DTS: Digital Theater Systems, a company that is rival to Dolby Labs.

The main difference between DTS-HD High Resolution and DTS-HD Master Audio is that the former uses lossy digital compression, while the latter's compression is lossless.

DTS-HD High Resolution (HR) and DTS-HD Master Audio (MA) each piggyback on the original DTS codec in such a way that each represents an "extension" to the "core" DTS. That is, a HR bitstream consists of a "core" DTS stream to which is added extra data, for more realistic sound and/or extra channels. An MA bitstream simply adds to that "extended" amount of HR data yet more data, for completely lossless audio.

Presently, all HD DVD and Blu-ray players can read full DTS-HD Master Audio bitstreams (which would include all DTS-HD High Resolution bitstreams, if any were present on discs). But they all merely discard the "extension" data and decode only the DTS "core" soundtrack, at up to a bitrate limit of 1.5 Mbps.

A better alternative would be to have the players ship DTS-HD Master Audio bitstreams as-is to external gear for decoding. I confess to not knowing which if any current HD DVD and Blu-ray players can do that.

Another fine alternative would be to have the player unpack DTS-HD Master Audio bitstreams to MLPCM for external use. It is not clear that any Blu-ray or HD DVD players can do that today. I imagine none can: if a player can't decode full DTS-HD Master Audio bitstreams, it surely can't transcode them.

I don't, by the way, consider full DTS-HD Master Audio support crucial in a future-proof home theater audio system. It and the lesser DTS-HD High Resolution codec (which, as far as I can tell, has been totally ignored by disc creators so far) are, after all, optional for both the HD DVD and the Blu-ray formats. You may never come across a disc that has either of them. And if you do, chances are the disc will also have the "equivalent" Dolby format as well: Dolby TrueHD, for DTS-HD Master Audio; Dolby Digital Plus, for DTS-HD High Resolution.

Furthermore, it looks as if all players from both camps will continue to be able to extract "core" DTS from the more advanced DTS codecs, into the foreseeable future — even though the ability to do so is, technically, strictly optional.

So there you have it. Each new high-def disc format supports a welter of old and new audio codecs, some of which offer more than 5.1 channels and/or lossless data compression. Depending on the format, these codecs can be mandatory or optional. Within each format, every disc must contain at least one of the mandatory audio codecs, and every player must be able to "use" every mandatory codec.

Codecs which are "used" by a player can optionally simply be downmixed for, say, 2.0-channel analog stereo output — not good enough, in my estimation, in a future-proof system.

Or, they can be converted to multichannel analog output (up to six channels including LFE). That's fine if you receiver can input it ... and if you don't mind running six wires between the player and the receiver. (But if you have one HD DVD player and one Blu-ray player, to cover both formats, good luck in finding a receiver that can accept multichannel analog inputs from both.)

Or, they can be output to external gear for decoding, without necessarily being decoded within the player. That's fine, too, as long as the external gear has a suitable decoder.

Or, they can optionally be unpacked within the player to multichannel linear PCM. That requires that the player be able to transcode its supported codecs to MLPCM, and that the external gear be able to decode MLPCM. It also needs a fast, HDMI 1.3 signal path.

Accordingly, MLPCM transcoding by players, MLPCM decoding and use by receivers, and HDMI 1.3 would seem to be the three indispensable attributes of a truly future-proof home theater system.


(There is a table in the Wikipedia article on HD DVD that lists which audio codecs are supported, either optionally or manditorily, by HD DVD, Blu-ray, and DVD. Click here to scroll to the "HD DVD/Blu-ray disc comparison," then scroll down a bit further to see the table.)

Saturday, July 07, 2007

Aiming Towards a New Living Room TV

Until last Sunday I had a 61" Samsung DLP rear-projector HDTV in my living room. A real behemoth, it took up one end of the room, what with its non-flat-panel bulk and the massive stand under it that raised it to the proper eye level, and that provided shelf space for the equipment that fed the TV its signals and routed sound to a set of home theater speakers.

The daughter of some good friends is just moving into a new house with her fiancé and they needed a TV ... so I sold them the Samsung DLP and threw in the stand and auxiliary gear as a housewarming gift.

And now I have an empty spot along the wall where the Samsung stood, just the right size for a 46" flat-panel HDTV to sit on its (included) mounting pedestal atop a sofa table that I already have in position to receive it.

The prime candidate right now to fill that spot is a Sony 46" BRAVIA® XBR® series LCD Flat Panel HDTV, model number KDL-46XBR2. Its little brother, a 40" KDL-40XBR2, now sits in my bedroom (see A New Bedroom HDTV for Me, Part I).

Although I complained in this blog (see A New Bedroom HDTV for Me, Part II and its multiple following posts) about the fact that the 40XBR2's panel brightness is uneven on certain supposedly uniform gray-scale test patterns, I find I virtually never notice non-uniformity on actual video material. All in all, the 40XBR2 has an outstanding 1080p picture, with nothing else really to complain about ... and I assure you, I do tend to get a little picky about picture defects.

I'm taking a minimalist approach to this one. When I bought the bedroom TV last year as well as, about three years ago, the 32" Hitachi plasma HDTV I have in my basement, I simply assumed I needed a multichannel audio setup to go with each TV. Plus, of course, a DVD player. Plus, naturally, a high-def cable box/DVR, which in the bedroom installation morphed into a TiVo Series3 DVR with two CableCARDs (see Three Cheers for TiVo Series3).

But with the new living room setup, I plan to forgo multichannel sound. I find that my ears are so bad — I have a hearing deficiency in the upper ranges — that I understand dialog best when I listen to audio coming from the bedroom TV's internal speakers.

I twigged to that when I did some experiments to see whether the bedroom Sony receives any audio signal at all from the TiVo Series3, given that the only signal path between the two is one HDMI cable. I knew that in theory, an HDMI connection is supposed to carry video and audio, both in digital form. But what if the TiVo Series3 didn't always send digital audio out on HDMI, or the TV didn't always use it?

I reckoned there should be no problem sending digital audio out to the TV if the channel I am watching is digital ... but what about the many cable channels that are still analog?

Or, what if the digital audio associated with the channel I'm tuned to is Dolby Digital 5.1? Will the TV be able to decode it?

In the case of an analog cable channel, there's no problem whatever. My assumption is that the TiVo Series3 digitizes the analog audio on the fly and outputs it in stereo ... as, I'm guessing, the digital format called "linear PCM" ("linear" means there's no digital compression; PCM stands for pulse code modulation).

In the case of Dolby Digital 5.1, the digital audio stream is probably being sent as-is to the TV, which handles it just fine.

In all cases, I hear perfectly adequate, quite understandable sound through the TV's excellent speakers. True, it's not surround sound, and there's not a lot of bass. But I don't really care.

That all means I can get away, wiring-wise, with:

  • plugging the TV into a wall outlet
  • plugging a second TiVo Series3 into the same outlet
  • hooking a TiVo wireless network adapter to the TiVo Series3 (the wireless connection allows downloading the TiVo program guide without the use of a phone line)
  • connecting the cable TV 75-ohm input feed cable to the TiVo Series3
  • running a single HDMI cable between the TiVo Series3 and the TV
... and that's it! That's the full extent of the wiring and cabling that will be needed. As I say, it's minimalist.

The two CableCARDs which I will thereafter have Comcast install in the new TiVo Series3, so that it can pick up digital channels, two at a time, won't need wires.

The only other thing I might get that needs wiring would be a DVD player — again, just a power-cord connection and an HDMI audio/video signal path to the TV.

I'm in no hurry to get the disc player. I figure it will be either an HD DVD player or a Blu-ray unit, for giving me high-def pictures. Or, ideally, if the high-def disc format war shows no sign of letting up, a combination player that handles both formats.

Right now, I feel the players from both camps are not ready for prime time. They cost too much, have too many missing features — some don't even play CDs — and take too long to boot up. I've seen one dual-standard combi player so far, from LG. The reviews say it lacks virtually all the niceties we have all come to expect from a video disc player. I can wait until these players have grown into a stable, no-problems maturity before I buy. Maybe next year.

Yet I'm planning for a disc player eventually. Paired with the TiVo, it will become the second (and hopefully last) piece of gear that I will need to feed the new TV. So where will the two boxes go?

Actually, I have space for them in a corner near the TV. The only sticking point is that they have to be elevated so nearby furniture won't block the IR remotes' sightlines to them.

I don't really need a rack unit that has low shelves that will never be used — so I've decided on a wooden display pedestal with cherry laminate finish from Dick Blick Art Materials. I'll be getting the one that is 24" tall, shown at the left in the photo to the right.

The pedestal, with shipping, costs under $200. Its horizontal surface is 15" square — not quite wide enough for a TiVo Series3. So I'm going to top it with a 1/2"-thick, 15" x 18" clear acrylic cut sheet surface, about $40 from JMK Displays after routing and polishing of its edges.

Unfortunately, the wooden pedestal is not slated to ship until August 20. Oh, well ... that leaves me with time on my hands to consider opting not for the KDL-46XBR2 but for the newest Sony on the block: a 1080p KDL-46XBR4 46" BRAVIA® XBR® series LCD Flat Panel HDTV.

(The relevant page on the Sony website listing the KDL-46XBR2 and KDL-46XBR4, among Sony's other LCD flat panels, is here.)

The new, "shipping in August" KDL-46XBR4 model updates the KDL-46XBR2 with several new bells and whistles. (I take it that that shipping timeframe, which could easily slip, refers to 8/31/2007, and not a day earlier.) The main new feature seems to be the ability to interface with a Blu-ray player or other high-def source device that sends 1080p video out on HDMI at a rate of 24 fps (24 frames per second).

24 fps is exactly the frame rate of motion picture film. It is also the frame rate at which the film's 1080p video transfer is recorded on a Blu-ray or HD DVD disc. Yet most 1080p HDTVs need to have the 1080p/24 on the disc converted to 1080p/60 within the disc player. These HDTVs can handle 1080p/60 input, that is, but not 1080p/24. The conversion to 1080p/60 compromises the smoothness of motion in the on-screen image.

With the upcoming KDL-46XBR4 in the picture, as I understand it, a Blu-ray player can send it unconverted 1080p/24 on HDMI. The TV will upgrade the 1080p/24 internally to a 120-fps frame rate. 120 fps is exactly five times 24 fps, so the upgrade is straightforward. Still, in doing the frame rate upconversion, the KDL-46XBR4 is supposed to optimize the moving picture's on-screen smoothness even further. This is due to what Sony is calling its Motionflow™ High Frame Rate technology.

The new Sony KDL-46XBR4 is also future-proof by virtue of its supporting the new HDMI standard, version 1.3. HDMI 1.3 is faster than the current 1.2 and supports all of the fancy new digital-audio formats that Blu-ray and HD DVD discs can optionally provide. Of course, that does not necessarily mean the new KDL-46XBR4 can decode them all! Time will tell on that. (Nor does it mean that the currently available Blu-ray or HD DVD players can read the most advanced of the new audio formats, if they are present on the disc, and export them as-is to external gear.)

Another nicety of the KDL-46XBR4, vis-a-vis the KDL-46XBR2, is that both the internal video signal processing path of the KDL-46XBR4 and the output display panel support 10 bits (not the usual 8 or 9 bits) for each of the three primary colors, red, green, and blue. That means colors on screen that are more accurate than usual, with more subtle gradations, and with less "banding." Banding, also called "false contouring," is the tendency for solid-color areas in the scene to separate into visually discernible bands or strips because their most finely graded shadings are compromised by digital signal processing.

Unfortunately, the announced price for the KDL-46XBR4 is a whopping $3,599.99. The KDL-46XBR2, now in closeout status, can be had for $2,969.99 at Best Buy as of today, 7/7/07. It can be bought from online discounters for as little as $2,409.50, with no tax and free shipping (click here for a list of price quotes from

There is also a KDL-46XBR3 model, which is just like the KDL-46XBR2 except for having a black bezel and mounting pedestal. For the privilege of having that extra touch of elegance, Best Buy Online charges you fully $3,599.99, with an "in store only" caveat. (In other words, you can't put the KDL-46XBR3 in your cyber shopping cart and see its discounted price. Hopefully it costs less in the store itself.) The best online price for the KDL-46XBR3 (click here) is currently $2,619.50.

Accordingly, it looks as if opting for the new KDL-46XBR4 would cost me up to an extra grand! Is it worth it? That's a question I seem to have plenty of time to ponder.