In the latest issue of Home Theater in the letter's section: 'Don' (from Iowa) asks the difference between multiplex cinema sound versus lossless bluray audio - what essential the answer was that Dolby Digital/DTS/SDDS sound on 35mm prints are all lossy... but that digital projected (DLP/LCoS) 'films' sound are PCM lossless audio - who knew? (I didn't).

My question though is (which the letter didn't address) how does HD lossless audio compare to past PCM/Dolby Digital AC3/DTS sound on laserdiscs (where compression of sound was a non-issue) - an example would be that the a film like 'Saving Private Ryan' where the bass is more noticeable on the laserdisc edition is almost but not entirely absent on the DTS DVD edition, not to say the mix is flawed but the compression almost elimates alot of the omnipresent bass from scenes where tanks are present. Another example: the DTS laserdisc of 'Armageddon' versus Criterion's Dolby Digital 5.1 soundmix, bass is noticeably tighter and when the Chrysler Building crashes durning the Manhattan meteor storm, when it land's the bass and treble is ear assaulting - the DVD edition doesn't hold a candle to it by a landslide.

Also, is sound on IMAX features lossy - I remember reading somewhere that the IMAX soundmix for 'Transformers I' was an entirely different mix altogether than it's standard theatrical counterpart.

Paging Josh Z...

My understanding is that until Dolby TrueHD and DTS-MA, all previous home video surround codecs were lossy and compressed, including that of laserdisc. Back in the days prior to DVD, the biggest selling point of DTS was that it was less compressed than Dolby Digital (or AC-3, as it was previously known) and therefore sounded better.

I recall that when the JURASSIC PARK DVDs came out, there was a big discussion over whether the DTS versions were messed up because the bass was less prominent and adjustments were needed. It may very well be that the differences you are hearing are due to faults in the re-mastering than in the codecs themselves.

I thought I remember hearing some laserdiscs had PCM but I can't be sure.

Were there any home a/v receivers that could even play PCM, back in the Laserdisc days?

Don't analog in's do that? I'm guessing some were out back then. I have a ton of laserdiscs and I don't recall ever seeing anything PCM. Hell, I doubt even if I saw it I would have known what is was. I do have a couple of DTS laserdiscs which are loud as well - Blown Away and Jurassic Park. What's funny is that I haven't hooked up my laserdisc player again ever since I bought my new Denon receiver. I guess I should to see how it decodes those.

OK, where to start?

PCM is an uncompressed audio format. No compression at all. CDs use 2-channel PCM.

Dolby TrueHD and DTS-HD are lossless formats. Although compressed, the decoded results are bit-for-bit identical to the master. Similar to a ZIP file. Assuming all other factors are equal (same soundtrack, same mix), there is no perceptible difference between PCM, TrueHD, or DTS-HD Master Audio.

All other home audio compression formats are lossy.

The studio master for any movie's soundtrack is PCM. (At least, since the digital age.) DLP and IMAX theaters also use uncompressed multi-channel PCM sound. All other theaters use lossy Dolby Digital, DTS, or SDDS. The theatrical versions of Dolby and DTS are different than the DVD versions. The theatrical version of Dolby is actually lower bit rate than the DVD version.

The average bit rate for a Dolby Digital track on DVD is 448 kb/s.

The average bit rate for a DTS track on DVD is 768 kb/s. However, some use the higher 1536 kb/s rate instead. This is rare.

The primary audio format on laserdisc was 2-channel PCM. Very early LDs may have had only analog audio, but from the mid-80s forward almost all laserdiscs had PCM audio. Any stereo or A/V receiver with a Toslink or coax digital input can process 2-channel PCM sound. Otherwise, the LD player can convert the PCM to analog and output it over the red/white analog RCA jacks.

Dolby Digital 5.1 was introduced to LD in 1995. The bit rate was 384 kb/s, which is lower than DVD. Discs with Dolby Digital also had a 2-channel PCM soundtrack.

DTS 5.1 was introduced to LD in 1997. The bit rate was (IIRC) 1400 kb/s, a little less than the maximum available on DVD but much higher than the average. The DTS tracks occupied the space on an LD where the PCM tracks would usually be, so DTS laserdiscs were not backwards-compatible with PCM gear.

The issue with bass on Jurassic Park had nothing to do with the compression format, and everything to do with the fact that the LD and DVD came from different mixes. The LD's mix had much higher bass levels. Some have argued that they were artificially boosted. The DTS DVD's mix had lower bass levels. Due to customer complaints, Universal eventually remastered the DTS DVD with more bass and reissued the disc.

Did I leave anything out?

out of curiosity, I'd suppose Super Audio CD is also lossless PCM - right? also, are there any new receivers where I can hook up my laserdisc player via toslink? as well having the standard HiDef audio decoding that is now commonplace.

second, why is Dolby Digital/SDDS compressed in film form? is that a space issue on the actual film. I'd assume 70mm film sound (5.1 discrete stereo surround / 5 front channel-mono surround) were also compressed

SACD and DVD-Audio are both lossless formats. SACD uses an encoding format called DSD. DVD-Audio uses Meridian Lossless Packing (MLP), which was also the foundation for Dolby TrueHD.

Any A/V receiver with a Toslink input will work fine with a laserdisc player. Assuming the LD player has a Toslink output.

Dolby Digital is printed in a strip along one side of the film print. And yes, there are space issues. DTS is provided on a separate CD-Rom that gets played in sync with the projector. I believe the issue there is bandwidth.

Most 70mm prints had analog audio, I believe.

Thanks for that long reply Josh. Very informative.

I feel like there could be some name changes to clear things up. Uncompressed, lossless and lossy are all too similar to those not in the know. Even reading through your response I had to go back and double check the term meant what I thought it meant.

I thought True-HD and DTS-HD were originals, but it turns out they are actually compressed.

However, is DTS-HD MA also lossless?

bandwidth on a CD-Rom is comprimized and compressed - ??? I don't understand that, but I believe you...

I'd assume that DTS-Audio discs are lossless like SACD and DVD-Audio, but for it's theatrical discs I guess it wasn't possible - I find that baffling.

I know that this is somewhat off the topic, but those in "analog-digital difference" camp - sound IMO in analog form, notably on vinyl does differ, to me it sounds fuller and has a warmth, bass can be lot more powerful - a case in point, the vinyl mix of the Chemical Brother's 'Dig Your Own Hole' had more bass amped into that edition. I now bring you back to the topic on hand

Well, there's only 650MB or so on a CD-ROM, depending on the track pitch. A DTS track should take up about as much bandwidth as standard CD audio. (I don't know if they have to use two discs per film or what.) I wouldn't be surprised if the reason they settled on their bitrate was because most (or all?) CD-ROM drives at the time could only transmit data at 1x - that would be why bandwidth was a factor. However, I don't know if the drives they used had the same limitations. Of course we all have much faster drives now, but I imagine they have to maintain compatibility with older equipment.

DTS CDs are not lossless. They use standard DTS at about the same bitrate as standard CD audio (something around 1411kbps). It's just that instead of 2 uncompressed PCM channels, they compress 5.1 channels into the same space.

Superman07, I see your frown face, but don't get discouraged that TrueHD and DTS-HD MA are "compressed." This is lossless compression like FLAC, and the same bits are there when it's decoded. It's just encoded more efficiently to make better use of space on the disc.

See if this helps:

Blu-ray Audio Explained

I'm not an engineer. I could be wrong about bandwidth being the issue. However, in any case, DTS on CD (whether movie or music) is compressed. Keep in mind that DTS is a multi-channel format, whereas regular music CDs are only 2 channel.

^That makes sense.

You can't put 5.1 PCM on a CD, but you can put a compressed 5.1 DTS track on a CD.

For another example of the bandwidth issue, consider that ripping a CD back then with a 1x drive would have taken as long as it takes to play it (or longer if it did error correction and such).

Josh, based on this:

and the chart over at AVS ( http://www.avsforum.com/avs-vb/showthread.php?t=1050507 ) I'm confused on their terminology of "Complete" versus "Decode". I assume decode means the player will handle the processing of the DTS-HD MA, but is it then limited to HDMI 1.3a? Or can it be passed over analog out? I assume that is a bit rate issue?

I have only one DTS CD - The TITANIC soundtrack.

When I deconstructed the audio tracks on it to increase the gain on the rear channels and LFE for a customized version (because the mix as is has rears that are so quiet you cannot hear them at all) I saved every individual audio channel to its own WAV file. I looked at the audio spectrum analysis (Adobe Audition is good for this) and the tracks are very close to lossless - very little compression. So even though it is compressed it is still VERY high quality sound. No compression artifacts, and very nicely detailed.

In that chart, "Complete" means the player can decode the audio to PCM or pass it as a bitstream, your choice. Some players can only do one or the other. Analog support is in the next category over, and if a player has complete + 7.1 analog, that means it could pass lossless formats over analog.

To pass it as a digital bitstream, the device must be HDMI 1.3. That spec doesn't guarantee that it will (see the pre-slim PS3, for instance), but 1.3 is required to allow it. When Josh's article was written in 2007, there weren't many HDMI 1.3 players, but they are much more common now. Decoding does not require HDMI 1.3, because in that case the player is sending unpacked PCM to the receiver.

When passing it over analog, the BD player's DACs will convert it to analog audio (instead of the receiver's DACs, which are used when the audio is a bitstream or unpacked PCM). Analog output could be done by pre-HDMI 1.3 devices, but some didn't do it to save on costs. Even now, it's not a standard feature because many people who are interested in it will just get an HDMI receiver. I wouldn't be surprised if it gets phased out eventually, just as it did on DVD players.

Thanks for clearing that up. I already knew some of what you posted, but once I read Josh's recap it occurred to me that even if a player can decode that quality codec, it may not be able to send it out of analog channels due to size constraints. Guess it's not an issue though.

No, it isn't. Analog audio uses separate cables for each channel; a bit primitive compared to HDMI, but it works fine. It is similar to what one gets from a CD player: the uncompressed PCM on the CD is converted to analog by the player DACs and then goes to the receiver and speakers by one cable for each channel (left and right).

With BD players that have multi-channel analog output, there are six cables for a 5.1 setup or eight cables for a 7.1 setup. That's six or eight cables to the receiver's analog inputs and six or eight cables from the receiver to each speaker. Plenty of bandwidth. By contrast, a single HDMI cable has enough bandwidth to transmit multi-channel PCM audio AND the full Blu-ray video signal. A "miracle of modern technology", and all that.

A miracle of modern technology that forgot to include locking tabs for the cable to plug in with.

Well, by "size constraints," I thought he was referring to the physical size of the player. That shouldn't be an issue either with current players, as they're quite large enough, although I imagine they'll get smaller as time goes on. (Although even the non-slim PS3 had things packed in pretty tightly.) It's more of a cost thing where they don't want to include all the extra DACs and connections.

Aaaaah, that brings back memories. I remember that debate, and the thread about how to get the replacement disc, and how to verify you had the correct one.

Sorry, I was actually referring to the bit rate size per channel that analog can handle.