Dolby Pro Logic Options

[StLouisRod]

Ok, I've searched the forum for an answer to this, but still don't truly know the answer.

It seems simple... I've ripped my CD's to lossless format (APE), and play them back on MediaMonkey, Foobar 2000, etc. through my SoundBlaster Live 5.1 and into my Logitech Z-5300 speakers.

The problem is that the dolby pro-logic information encoded in all CD's, and thus in my lossless rips as well, does not play through the rear surround speakers properly. Sure, sound comes out, but it's simply a copy of the front speakers. Using the speaker's control panel set to Matrix, it simulates the center sound speaker and surround speakers, but not using the actual dolby pro-logic encoded signals within the music.

So how is it possible to play sound files via my 5.1 speakers in true dolby pro-logic mode?

[smok3]

i guess your talking about analog connection? afaik there is no proper software pro logic decoder, but you can take a look at the http://matrix-mixer.sourceforge.net/ (shrug)

[precisionist]

edit: The link above tends to mislead. StLouisRod's question has nothing to do with digital audio (if I interpret it correctly)
pro logic info in all CDs ? sounds very strange...
As far as I know, pro logic is a sort of wanna_be_a_sourround_sound in an analog way. It is an old format (pre-dolby digital/AC3) and was (is ?) preferably used on TV soundtracks/music. My old (~1990) receiver can detect pro logic info; I don't know how the info is mixed into the stereo analog signal. Is this signal playable as stereo at all, sounding like stereo ?
Second thing which might also be called 'pro logic' is a trick used by the receiver (mine does it):
It calculates a 'centre' channel from L+R and a 'rear' channel from L-R (or R-L) and adds reverb to the 'rear' channel.

This post has been edited by precisionist: Dec 8 2004, 16:41

[StLouisRod]

Wow! It's amazing that nobody seems to realize that virtually all CD's are mastered with dolby pro-logic encoding! My entry-level 1995 era Sony receiver, as well as my Harmon Kardon AVR75 are able to play back CD's in this mode. I would think most other receivers with DSP modes can as well.

The center and rear surround (mono) information is specially encoded within the music. If you are listening in plain stereo, then the information is simply mixed in with the left and right channels.

I used to enjoy a "trick" with my Sony receiver whereby I was able to turn off the front speakers and only listen to the rear surround speakers. It was fascinating to hear what instruments or effects (like delay, reverb, etc.) were plucked out and sent to the rear channels.

For a very vivid example, listen to the rear channel on Aerosmith's "Walk This Way". The lead guitar on the bridge to the chorus literally jumps out of nowhere! Because it's so isolated, it sounds like Steve Perry is sitting right there on your sofa playing guitar.

So yes, my question is, what software player and plugin can be used to decode this pro-logic information from my analog CD's and lossless audio files, and send it to the center and surround speakers properly?

I tried the matrix program, but I'm not sure I understand how to use it. Does it affect all directsound programs running? If so, I tried playing songs and moving the gains up and down, but there was no audible difference. And the pro-logic-ness certainly wasn't apparent either.

[Mono]

Actually the CD does not need to be mastered for Pro Logic for the processor to work (the "surround" effect you are getting more often than not is a result of the decoder and not the encoder and decoder). Grossly oversimplified, the matrix encoder mixes the center equally into L and R (with a volume reduction of 3dB) The rear channel (yes, just one channel) is mixed equally into L and R with a highpass and lowpass, a noise reduction process, and two phase shifts. (If I have made any errors please correct me.)

To decode any source (since there isn't some automagic flag that marks a stream as "Pro Logic") the passive decoder takes the difference of L and R, performs the phase shifts and noise reduction and lowpass. The active decoder uses more processes to enhance separation between channels, but the effect is essentially the same.

[Corby]

Ever tried with PowerDVD or WinDVD??
They have ProLogic decoders and can play audio CD's.

[precisionist]

Actually the CD does not need to be mastered for Pro Logic for the processor to work (the "surround" effect you are getting more often than not is a result of the decoder and not the encoder and decoder). Grossly oversimplified, the matrix encoder mixes the center equally into L and R (with a volume reduction of 3dB) The rear channel (yes, just one channel) is mixed equally into L and R with a highpass and lowpass, a noise reduction process, and two phase shifts. (If I have made any errors please correct me.)

To decode any source (since there isn't some automagic flag that marks a stream as "Pro Logic") the passive decoder takes the difference of L and R, performs the phase shifts and noise reduction and lowpass. The active decoder uses more processes to enhance separation between channels, but the effect is essentially the same.

Ah, so the two things I mentioned in my first post are the same ?

[DonP]

I have a CD mastered with Pro-logic, but most aren't. If the producer went to the trouble (and I would think license expense) to master in Pro-logic, I would expect some notice on the CD case so the user knows to turn it on.

[krabapple]

Wow! It's amazing that nobody seems to realize that virtually all CD's are mastered with dolby pro-logic encoding!

That's because they aren't.

Pro Logic will do *something* to a 2-channel signal sent to it -- but that doesn't mean the source was mastered with Pro Logic processing in mind. THere may be a few CDs that were intentionally mastered for Pro Logic playback...but they're rare.

Pro Logic II, the successor to DPL, was designed *explicitly* to accept *any* two-channel stereo mix as input, and render it into a reasonable simulacrum of 5.1. It will also properly decode stuff that was mastered with Pro Logic playback in mind (e.g., DVD soundtracks). But again there's few or no CDs that were mixed with DPL II *in mind* -- that is, mixed to anticipate what would happen when DPL II is applied. It's possible to do, but I don't think it's done much for CD. Instead, DPL II just takes what's in any given two-channel mix, and applies sophisticated 'channel steering' logic to it. It applies the same logic to all sources, but since each CD mix is different, the results will vary. Some CDs 'decode' really strongly into surround channels (e.g. Can's "Tago Mago', IME), others sort of just sit there, with at most some added ambience in the rear channels.

Personally, I love DPL II, and use it on everything -- sometimes I even prefer the DPLII generated 'surround mix' from the stereo track, to the multichannel mix a mixing enginner has created for a DVD-A or SACD surround release.

There are other DSPs like DTS Neo, and Logic 7, that do something similar to DPL II.

The newest version, Pro Logic IIx, does the same trick with 5.1 sources -- it can synthesize more surround channels from them.

Lossless compressed audio files should 'decode' in to 'surround' via DPL II exactly the same as they would from the original CD. I know mine do, using Foobar2K as the FLAC file playback interface to my hard drive, and running the signal from a digital coax out of my soundcard into my recevier for DPL II Music playback.

This post has been edited by krabapple: Dec 10 2004, 00:28

[Mono]

Ah, so the two things I mentioned in my first post are the same ?

Yes, though your receiver isn't "detecting" Pro Logic but processing the audio as if it were PL anyway.

[RockFan]

Pro Logic will do *something* to a 2-channel signal sent to it -- but that doesn't mean the source was mastered with Pro Logic processing in mind. THere may be a few CDs that were intentionally mastered for Pro Logic playback...but they're rare.

....

Personally, I love DPL II, and use it on everything -- sometimes I even prefer the DPLII generated 'surround mix' from the stereo track, to the multichannel mix a mixing enginner has created for a DVD-A or SACD surround release. 

exactly so. Prologic 2 (and earlier multiplexers) create a centre channel from any 2-channel or stereo source thru fairly simple sum-and-difference circuitry, that's the front three.

The discreet rear effects in a true Prologic encoded 2-channel mix are created with more complex phase-shifiting algorithms.

It just happens that most ambience and reverb in a straight stereo mix is slightly out-of-phase (by definition) with the primary mike source, and is processed into 'surround' or rear effects by DPL2.

BTW, some SACD's are being released which have original stereo recordings mastered to 3-channel (which is intruiging), in exactly the same way as DPL2 accomplishes it 'down-stream', but with the benefit of the presumably higher fideiity discreet DSD channels.

ciao,
R.

[2Bdecided]

BTW, some SACD's are being released which have original stereo recordings mastered to 3-channel (which is intruiging), in exactly the same way as DPL2 accomplishes it 'down-stream', but with the benefit of the presumably higher fideiity discreet DSD channels.

It's only better if their 2>3 processor is better than yours. I doubt it's implemented in the DSD domain!

Unless there's a genuine 3-track master tape available (likely from the late 1950s onwards) and this is where the 3rd track came from, I'd expect "purists" to avoid this.

FWIW I'd love to hear the original 3-track tapes copied onto SACD or DVD-A for many artists from the 1950s and 1960s. I've heard some of the masters at the AES and they sound stunning.

Plus you could mute Elvis and sing Kareoke to his backing band, or mute the band and listen to a great Elvis solo. Which, unfortunately, is why they don't release them this way. It's a great shame.

Cheers,
David.

[RockFan]

It's only better if their 2>3 processor is better than yours. I doubt it's implemented in the DSD domain!

Unless there's a genuine 3-track master tape available (likely from the late 1950s onwards) and this is where the 3rd track came from, I'd expect "purists" to avoid this.

FWIW I'd love to hear the original 3-track tapes copied onto SACD or DVD-A for many artists from the 1950s and 1960s. I've heard some of the masters at the AES and they sound stunning.

Plus you could mute Elvis and sing Kareoke to his backing band, or mute the band and listen to a great Elvis solo. Which, unfortunately, is why they don't release them this way. It's a great shame.

Cheers,
David.

It could be that some of those 3-channel SACD's are doing this, and you're right, it would be something to hear those recordings as 'sessions' rather than mixes.

I should say I'm no SACD zealot, I would prefer high-res PCM (such as DVD-audio) - the development of PCM decoding (DACS) is 'open-ended', unlike DSD.

And yes, I doubt those 3-channel mixed are done in the DSD domain, probably high-res PCM, and then conversion to DSD at mastering.

ciao,
Rainer.