Enhancing Audio for Dolby Prologic

[tygrus2000]

I've read thru a number of threads on the Prologic and Prologic II debate and near as I can tell, Prologic is just a surround upmix or enhancement of a traditional stereo mix done by a hardware decoder or receiver giving a more spatial feel to the audio. However, I caught a small part of a thread saying something about being able to use an audio program like BeSweet to "enhance" stereo mixes so the decoded effects in Prologic are more pronounced. Anybody have any more info on this and how to do it.

thx in advance.

tygrus

[SupaCoopa]

First some theory, as I'm feeling blabby today!

Dolby Prologic carries four-channel surround information (Center, Left, Right and Rear) as opposed to two-channel (L & R) of Stereo signal, so they're two different things altogether. A fairly complicated "analog" algorithm is used to combine the two extra channels into the stereo signal and a Prologic decoder is needed to extract those two channels and direct them to the relevant speakers during playback. If you playback a Prologic encoded signal on stereo-only equipment you just get L & R (as the two extra channels cannot be identified and decoded), if you use Prologic equipment you get all four channels and a satisfactory surround soundfield.

Now, if you playback non-Prologic stereo signal on Prologic equipment, you'll either get normal L & R from the two relevant speakers only or, on some more advanced equipment, a "wider" L & R that comes from all speakers. Some equipment refer to this as "virtual dolby surround", but this is not surround by any means. Basically, you get L from the left, R from the right, combined L&R from center and combined L&R from (one or two speakers at) rear, possibly with some time delay added. Some two-channel systems (such as TVs) can "spatialise" stereo to give a "wider" impression, by directing L & R signals to the opposite channel, again with some time delay.

Most Dolby Digital ampilifiers also have "DSP programs" that put all speakers to use when if you only feed them two-channel input. It's just a matter of taste, whether you'll find any of these better than plain stereo playback, keep in mind that you'll completely lose channel separation, which is an important figure. To me, all of these methods produce a soundfield that may appear impressive at first, but gets tiresome soon. You may find some use for them in movies, but you definately won't like your music played back this way.

So, to (kind of) answer your question, if you use BeSweet (or CoolEdit, SoundForge etc) to "widen" a stereo soundtrack, you basically mess with the channel seperation the way an amplifier (or computer sound card) can do at a press of a button, but you'll permanently distort the soundtrack. You may like the result, you may not. But if you don't... there's no way of getting the original back. You can encode a soundtrack to real Dolby Prologic using SoftEncode (a now defunct program that can also encode Dolby Digital) but what will you use for center and rear if you only have a stereo soundtrack to begin with? Movies with Prologic soundtrack have seperate information at these channels, dialog only at center or bangs and booms at rear only, that's why they produce a satisfactory soundfield. A very good example of a well-put-together Prologic soundtrack is the "Blair Witch Project".

Prologic II is closer to "virtual surround" than it is to Prologic. It employs a Dolby-patented sophisticated algorithm that turns any stereo signal to pseudo-surround during playback. This works way better than any of the above "virtual surround" or "spatialise" methods, but again it's a matter of taste whether you'll prefer to use it or not. You can't encode a soundtrack in Prologic II, it's just a (very well thought) DSP program relying on applying acoustic tricks during playback to a two-channel soundtrack.

Hope this is of some help, but the definate judge is always your ears!

[tygrus2000]

Thx. for the info. Thats definately helpful. Could you perhaps give a few pointers on exactly how SoftEncode can make prologic encoded audio files? I have used it before for Ac3 mixes but I have never heard anything about this function.

thx.

tygrus

[Oracle]

from supa..

Prologic II is closer to "virtual surround" than it is to Prologic. It employs a Dolby-patented sophisticated algorithm that turns any stereo signal to pseudo-surround during playback. This works way better than any of the above "virtual surround" or "spatialise" methods, but again it's a matter of taste whether you'll prefer to use it or not. You can't encode a soundtrack in Prologic II,

2 Points-
Prologic II is not closer to Virtual Surround,??? its an enhancement of Pro-logoc 1, look at the specs on www.dolby.com e.g 3/2 and more bandwidth/seperation for the surround chanels.

You can optimise an encode for PLII eg surround 2 in Be-sweet & Headache

[Oracle]

also from www.dolby.com

PLII MIXING

There is a difference to `Dolby Surround (PLI)` ,have a read

3.12 Mono, Stereo, and Dolby Surround Compatibility
Mixing techniques used in Dolby Pro Logic II productions are similar to those used in normal stereo productions. Just as you should check the mono compatibility of a stereo mix, you should also check the mono, stereo, and Dolby Surround compatibility of a Dolby Pro Logic II mix.

Dolby Pro Logic II mixes are consistently compatible with Dolby Surround decoding. The main difference is that the Dolby Surround decoding band-limits the surround channel to 7 kHz and the surround information is mono.

In most cases, stereo compatibility is not an issue. The mix's surround element will appear to be outside of the speakers, as would an out-of-phase signal. Notice that the entire mix should not sound out-of-phase, and there should still be a hard center image.

Mono compatibility is a little trickier, because any content that is in the Surround channel disappears in mono. This is an asset in some cases and a detriment in others.

In situations such as live sporting events, losing some crowd information in the mono mix helps those at home listening in mono on a three-inch television speaker to hear the announcers more clearly. In other applications, the mix may have a critical element in it that is predominately in the Surround channel. For this reason, surround elements should also be present in a front channel, interior panned, so they will be heard in mono, as is commonly practiced in the film industry.

[mkelley]

You can encode a soundtrack to real Dolby Prologic using SoftEncode (a now defunct program that can also encode Dolby Digital) but what will you use for center and rear if you only have a stereo soundtrack to begin with? Movies with Prologic soundtrack have seperate information at these channels, dialog only at center or bangs and booms at rear only, that's why they produce a satisfactory soundfield.

But what if I *do* have soundtrack information to use for the center and rear?

I'm not interested in copying movies, but in making my own. When I transfer my own videos over I convert the stereo tracks (using BeSweet) into AC3. However, I can also create other tracks to enhance the film -- could I use SoftEncode to process all this together into a 5.1 soundtrack on the DVD?

But if SoftEncode isn't available anymore is there another (cheap) way to do this? If this is going to end up being prohibitively expensive I'm not interested, as it's unlikely my efforts will ever be seen by anyone other than friends and family <g>.

[Quigonsean]

What I'd like to know about all this isI do have softencode 5.1) I am currently working on the StarWars spec ed tril. I believe it is prologic, and will soon be doing Mask of zorrow that is. Is it possible, to take the 2 channel file capped and demuxed, and extract the info and additional tracks used by a prologic decoder so I can feed them into softencode, or besweet. I would assume since prologic can be done on vhs it all 4 chanells are carried through the stereo composite outs, and hence it is possible then that the prologic info is present in the audio on a vhs capture. I'd like to extract the extra audio to encode to a 5.1ac3 file. Generating the extra 2 tracks beyond prologig would be complicated, but possible. So can this be done? and if so how? I do have Softencode 5.1, BeSweet, Cool Edit Pro 1.2 registered full version, and a registered copy of cool edit96. Oh and Cakewalk proAudio 7.0. (I do A small music recording studio for hobby)

Thank You to All,
Sean Ward
quigonsean<nospam>@comcast.net

[SupaCoopa]

Oracle:
You're right, you can indeed encode stuff in Prologic II. It seems I've been skipping my homework regarding Prologic II... I wrongly had the impression that it is a playback only "technique", but after reading again the Dolby documentation it is obvious that you can encode soundtracks in the same way you do with Prologic. On-the-fly re-mixing of stereo soundtracks to multi-channel is just one of the additional features Prologic II systems offer. However I have yet to come across any movie specifically featuring Prologic II encoded soundtrack.

Tygrus2000:
I have to get back to you about this. I think the Prologic options are at the same screen along with the other encoding options, to the right. This is were you specify the number of channels for the encoded soundtrack, bitrate and stuff. I haven't tried making stereo Prologic, I prefer Dolby Digital 5.1 for obvious reasons, but I think the way to go is to specify 3/1 channels and enable something like "include Prologic information" or something. When I get back to my home PC I will look to it

Mkelley:
Yes, you can create other tracks to enhance the film's soundtrack and use SoftEncode to produce a Dolby Digital soundtrack. You can, for example, use your normal left and right chanels to L & R, same channels with "stereo expansion" and time delay to the rear L & R (to have a wider soundfield) and possibly a speak-over at the center only. Or you can have normal sound coming from the front and accompanying music from the rears. You get the picture... I use SoftEncode as it is easy to use (if a little slow), some Cubase/Steinberg sound editors offer Dolby Digital encoding too but they're a pain to use and VERY expensive. You can find SoftEncode the same way you can find DVD Maestro or other useful but defunct programs...

Quigonsean:
If you have a two-channel Prologic encoded soundtrack to begin with, there is no extra work involved. You record in stereo, so you have a two-channel wav file. You convert this to Dolby Digital 2.0 and you now have a stereo AC3 containing Dolby Prologic information. To my knowledge, due to the fact that Prologic channels are not discreet the way Dolby Digital channels are, you can't "extract" and seperate them. But maybe Oracle can prove me wrong...

[Quigonsean]

Thanks Coopa, boy your a fountain of knowledge. I really appriciate the help. I did find a post here with a link to an app the poster wrote. The app converts Dolby Dig,Pro Logic, ProLogicII, and old fashion dolby surround to multi channel mpeg. With that I may be able to transcode a prologic track into Multi channels, that is if I can get the multi channel mpeg into its 4 seperate channels. But I may not have to, I just glanced quickely at that app, and I think it will split the single rear surround to 2 tracks LS, and RS. Then I just need to parse the mpeg into 6 mono channels then I can encode with softencode. If that works it will rule, but then I'll be agitated that I can only cap my audio with WinDVR(Currently my fav capping app) into MP1L2 at 384khz and not higher for a little better 5.1 track once all said and done. One thing that is cool is my brother in law also does a small recording studio as a hobby, and besides Pro-Audio he uses Acid-Pro, so for a homemade video I can mix it and all on his setup with AcidPro, and export to Softencode for an origanal 5.1 sondtrack on my home movies, if I wanna go through all that. I probably will at least once, that way I learn how to do it.

Anyway, once again thank you for your help. Oh btw here is that app I was talking about. http://hypercube.is.dreaming.org/ It looks really awsesome, especially for a free app. I wish I could write programs, but I ain't got the patients to learn to code.

Thanks,
Sean

[Oracle]

Coopa, I think the mixing docus are new as when I last looked about six months ago it was not there.

I dont think you will ever find a movie(DVD) advertising it is encoded for PLII, as why bother when probably(guessing here) every PLII reciever can also decode dolby digital. Its probably more intended to enhance the old PLI recordings.& Maybe newer programs on TV/Sat which transmitt with 2 chan sound are optimised for PLII as its backward compatible to PLI(also guessing again)

[Quigonsean]

I'm trying to use the PLI and II for my DVD's I make from VHS Like the StarWars Trillogy is in PLI if I can get it "Decoded" so to say into the 4 pl channels I can then split the rear for a 2 speaker mono surround stereo front mono center, and then use the whole mix with a 80hz low pass filter to generate the LFE.

I ain't having luck though. I demuxed it with Tmpegenc got a .m2v, and .mp2 that are 2H7Min28Sec. I run the .mp2 through BeSweet so I can use hypercube to trancode the pl1 sig to 5.1ac3, guess what the ac3 that BeSweet kicks out is 1hr57min48sec a differance of 10 minutes. Now I've had a DVD rip where the audio was 3minutes shorter than vid, and Maestros "Create Audio Synch Track" works fine fixing it and keeping audio is in perfect synch, but as good as it is it ain't gonna fix 10 minutes. I was really hoping to turn the pl1 soundtrack into 5.1 ac3 but till I can get the mp2 transcoded but the correct length I'm stuck with a mp2 but at least it is plI, better then plain stereo. Oh well, if anyone has any ideas. I tried using the ac3 in hypercube to generate 6 pcm files then made my 5.1dd in softencode, but it was 10 minutes off cause of the ac3, and hypercube only accepts ac3 to transcode plI&II etc... . I tried making a multi channel mpeg with hypercube, then convert to .ac3 5.1 in BeSweet, but same thing because the ac3 I started with is off. At leastr I know it can be done and how. I just gotta find out why BeSweet makes my org mp2 thats the correct legnth get short.

Thanks for all the help everyone,
Sean Ward

[Quigonsean]

I forgot to ask. Is there another app to convert my .mp2 to ac3 ? I think headac3h can do it, but every post I've seen on headac3he is a post saying it crashes with an error, and I've never seen a fix everyone just says "Use Besweet" I know if I can get the .mp2 converted to ac3, but with the correct length, and PL I information Hypercube in .pcm mode then softencode will work and work great. It is just a matter of getting the mp2 to stereo 2.0 ac3 with pro logic info still intact because ac3 in either 5.1, 2.0 pro logic 1or2, or ac3 2.0 stereo non pl is the only input format hypercube accepts.

Thanks
Sean