Laserdisc PCM to low compressed AC3

I know, I know, laserdisc PCM soundtracks should be left "as is" (when possible, because they must be converted at least to 48KHz to be BD/DVD/AVCHD compliant), but I did my projects with several soundtracks in different languages, and I guess I could spare a little bit of disc space compressing them, and leave video more space. You know, adding four PCM soundtracks could "eat" something like 9/10GB disc space, and leave only 15GB to video in a BD-25...

As there are wonderful LD AC3 5.1 discrete soundtracks (and they are all 384kbps), I think a PCM 2.0 could be compressed with little or no artifacts at 640kbps (for BD/AVCHD) or 448kbps (for DVD) - or even less. I thought also to use DTS, but to achieve a similar quality I should compress at higher bitrates, and AC3 decoder are a little more spread than DTS ones.

Ideally, it could be converted to DTS-HD MA or Dolby TrueHD, but I know no software (free and/or open source) that could do that, and these kind of decoders are less spread than AC3 and DTS...

Opinions?

Dolby's suggested bitrate for 2.0 in AC3 in 192 kbps. This is transparent to me - I cannot tell the difference between uncompressed PCM and a 192 kbps AC3. This is not opinion, this is fact: proven via a double-blind ABX test.

This is not to say that 192 kbps is transparent to everyone; it's possible that there are some people, maybe with better ears or better equipment, who can tell the difference. I also suspect it's quite likely that some people think they would easily be able to tell the difference, but if they actually tried to prove it via an ABX they would fail. 

When it comes to audio, opinions are quite often bullshit. I would advise you to spend some time reading on listening tests at the hydrogenaudio.org forums, and try some tests of your own.

It is even possible that some people would be able to distinguish between 640 kbps AC3 and the uncompressed original. The only way to be sure your audio is transparent to everyone is to keep it uncompressed, or use lossless compression. As far as I know there is no free or open source software that can compress to DTS-HD MA or Dolby TrueHD, but if you wanted to release your project as an MKV instead of a structured BD you can easily include lossless FLAC audio.

You wouldn't even need to do a 44.1 to 48 kHz conversion, saving another potentially non-transparent stage, but I'm not sure how well hardware players would support playback of an MKV containing 44.1 kHz FLAC audio.

Another thing I thought is the following: as it seems there is no proper Dolby Surround/Dolby ProLogic software encoder, it is still possible to capture the analog out of a Dolby ProLogic hardware decoder, and then use the captured sountrack to build up a discrete soundtrack for a project, using low compressed AC3/DTS...

A "simple" uncompressed PCM is the most logical way - even a low compressed AC3 should retain the Dolby Surround matrixed signal - but I wonder if the former technique will result in better (or different) audio, as the Dolby ProLogic (hardware) decoder should first convert analog matrixed stereo signal to digital, then decode it to four discrete channel, and convert back to analog, while a Dolby Digital simply "disassemble" the digital stream, so no ADC is involved...

It will be interesting to make some tests, as there are certain Dolby Surround tracks that are better than their discrete counterparts...

Opinions?

FWIW, I agree with Moth3r that in nearly all cases, 192k AC3 should be just fine for 2.0 tracks.  I tend to encode all "alternate" tracks (dubs, commentary, etc) at 192k and think it's perfectly reasonable.  For "main" tracks, though, I throw just a hair more bitrate at it (no objective reason for this)--if I don't do lossless, then I do 224k AC3 for "main" stereo tracks.  Those are the only two bitrates I've ever seen on mainstream commercial discs for DD stereo tracks.  Mastering differences account for most if not all of the differences you might hear between a lossy DVD tracks and the equivalent lossless Blu-ray track.

You can save a lot of space, without sacrificing quality, by encoding mono as a single channel.  i.e. on Laserdiscs and many other media, mono tracks are encoded as two identical channels for left and right.  If you encode it as a single channel, you can get away with half the bitrate--96k or 112k using my methods above.  Some people don't like single-channel mono tracks because of how some receivers don't upmix them the way they want, but you can't please everyone.

FWIW nobody's arguing that LD audio doesn't frequently sound better, but I'd argue it's more a function of the medium's age than its capabilities.  Studios futzed around with audio in the Laserdisc era, certainly, but the technology wasn't so ubiquitous--someone had to actually decide to futz with the audio if they wanted to do it, and the ways they could mess with it were limited.  Now, it's just assumed that audio will be heavily processed for a home video release, and someone needs to decide NOT to if they don't want that to happen.

Which is why, generally speaking, LD audio beats DVD audio, but DVD audio still manages to beat BD audio on at least some titles.  Lossy or lossless doesn't enter into it, it's the mastering.

I'd like to add that many (me included) think that the AC3 soundtrack found on laserdisc is (usually) better than DVD - even when DVD is at 448kbps - because LD *should* be the same, or really low processed, of the theatrical soundtrack...

Further "blah blah blah" here! (^^,)

dwalkerdon23 said:

...this is the AC3 Pro Logic of track of Titan A.E.  converted to Flac.

converting it to FLAC removes Dialnorm & DRC & brings it back to its normal volume.

Wouldn't it be easier to just disable DRC on your decoder and turn the volume up?