DVD-Audiobahn New DVD-Audio music releases and talk about the latest players.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ DVD-Audiobahn ]

---

[ Alert Moderator ]

---

In the end, it's supposed to be the same.

Posted by Michi (P) on September 26, 2005 at 22:42:18

In Reply to: Yes, my Denon 1600 uses the PPCM designation.... posted by Chris Garrett on September 26, 2005 at 22:09:30:

At least that's the premise. MLP/PPCM as a lossless algorithm should technically give out exactly what it got in. It's the same flavor of CODEC as FLAC, ALAC, and Monkey's Audio. (All of which, by the way, are more efficient than MLP, at least in stereo.)

I'm not going to even touch on arguing the 'differences between MLP and DSD' - that's not an appropriate comparison. DSD has a similar lossless packing schema called DST; MLP is a compression method, not a modulation or encoding method.

So the result is still PCM. LPCM is rather wasteful and has a lot of redundant data. Especially, for example, during absolute silent passages, you're storing a run-length of zeroes that could be packed into a dictionary and pattern-repeated.

Again, in its most basic, if you put 110001101 PCM into MLP, you should get 110001101 out. However there are some caveats.

There's an option in MLP to use their ReBit (yes, (TM)) algorithm. This 'watches' the dynamic range of a given block and reduces bit depth accordingly: supposedly it will never reduce the effective bit depth to any lower than is actually used by the audio, but in a world of DACs and ADCs with widely varying noise floors, I'm not so sure what this means. One "rule" of ReBit, however, is that it will never reduce the bit depth to below 16 bits, under any circumstances.

ReBit is optional, and its savings are, in my opinion and experience, negligible. A three-odd minute stereo track at 192/24 will compress from 250mb in LPCM to 165mb in PPCM(MLP) without ReBit. Of course, depending on the characteristic of the signal, this would vary, but on good days the best I've seen is 155mb on that same track when using ReBit at its maxiumum.

Now, of course, there's a savings increase with multichannel since you have a few more dimensions of redundancy to work with. (Similar to why 448kbps Dolby Digital 5.1 is not the equivalent, channel per channel of, say, Dolby Digital 2/0 @ 148. You have M/S matrices to deal with and in general a 5.1 signal will yield a higher ratio of compression than a 2/0 signal.) The rear channels can be given more ReBit latitude than the front and center channels. So in a conservative mix you could see Ls and Rs and C running at 96/16 almost full time, and Lf and Rf running at 96/24 or a minimum of 96/20, selectable in the encoder.

Again I'm not so sure about the intelligence of the MLP encoder when it comes to applying ReBit, so in that sense you could posit an argument that MLP is not truly lossless when this option is used.

But, without it, you're just talking about entropy and dictionary encoding which should not touch the sound or even the resultant decoded LPCM in any way shape or form. In theory you should be able to take a 250mb LPCM wav, run it through MLP and create a 165mb MLP file, decompress that MLP back to WAV, and the resultant LPCM file and original LPCM file should be bit-for-bit identical.

But it's all PCM. Comparing it to DSD is like comparing .ZIP to .JPG... they operate in different domains.

This post is made possible by the generous support of people like you and our sponsors:

VH Audio

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---