A better Dolby Pro Logic II downmix

[bleo]

The Dolby Pro Logic II downmix used in programs such as Azid.dll, BeSweet, HeadAc3he and AC3Filter, was derived in this thread: http://forum.doom9.org/showthread.php?s=&threadid=27936

A test sample of 5 channels active one at a time, downmixed to 2 channels with this matrix, should be able to be decoded by a Dolby Pro Logic II decoder back to the original 5 channels. However, I have been disappointed by the rear channel separation of the current DPL2 downmix.

The rear channel separation can be improved by altering the 'balance' of the surround channel downmix while maintaining constant power. That is, BL is downmixed more to Lt, while BR is downmixed more to Rt. However, by skewing the balance too much to either side, we lose phase information, resulting in reduced front-back separation.

Here I describe a method for deriving a better DPL2 downmix

Methods
Contents of 5.1 AC3 test source 'Avia ac3test' (http://www.digital-digest.com/dvd/downloads/trailers.html)
time (sec) channel contents (announcer says: )
12-14 L 'left front'
14-16 C 'centre'
16-18 R 'right front'
18-20 BR 'right surround'
20-22 BL 'left surround'
22-24 L 'LFE'
LFE [rumble]
'surround2' downmix
"C:\tmp\BeSweetv1.5b19\BeSweet.exe" -core( -input "c:\tmp\ac3test.DELAY 0ms.ac3" -output "c:\tmp\ac3test.surround2.wav" -2ch -logfilea "C:\tmp\BeSweetv1.5b19\BeSweet.log" ) -azid( -s surround2 -L -3db )

'4.8 dB' downmix
Using AC3Filter in GraphEdit. Exact values of surround downmix coefficients are SQRT(3/4) and SQRT(1/4). The surround power difference is triple, hence 4.8 dB

Lt = L + 0.7071 C + 0.7071 LFE - 0.866 BL - 0.5 BR
Rt = R + 0.7071 C + 0.7071 LFE + 0.5 BL + 0.866 BR

'6 dB' downmix
Lt = L + 0.7071 C + 0.7071 LFE - 0.8944 BL - 0.4472 BR
Rt = R + 0.7071 C + 0.7071 LFE + 0.4472 BL + 0.8944 BR


DPL2 decoding as per thread: http://forum.doom9.org/showthread.php?s=&threadid=57736

Notation of decoded channels: L' R' C' LFE' BL' BR'

Screenshots taken from Cool Edit Pro

Separation between channels calculated from difference in total RMS power of 2 sec segments

Results
Figures at http://www.geocities.com/bleo98

Figure 1: surround2 BL'
18-20 sec, BR leaks into BL'. Separation ~ 9 dB

Figure 2: 4.8 dB BL'
18-20 sec, more separation between BL' and BR' ~ 26 dB

Figure 3: 6 dB BL'
18-20 sec, even more separation between BL' and BR' ~ 31 dB

Figure 4: 6 dB L'
BUT! 20-22 sec, BL leaks into L'!

Figure 5: 4.8 dB L'
20-22 sec, no leakage of BL into L'

Discussion
The 4.8 dB downmix provides optimal separation of all 5 channels. I now use this matrix in AC3Filter, but should the azid.dll matrix be changed?

surround2 is quieter because the downmix coefficients were normalised to prevent arithmetic overload. The 4.8 dB and 6 dB coefficients are not normalised. Overload would only occur if all 6 channels were at full scale during EXACTLY the same time sample, which is highly unlikely. In fact, this did not occur during testing with the Lord of the Rings soundtrack.

The 'pulses' every two seconds are steering artifacts: a delay in steering inherent in the decoder's feedback design (?)

DPL2 cannot steer 5 independent channels simultaneously. For example, during 22-24 sec, L contains 'LFE' and LFE contains [rumble]. Note, LFE is supposed to be decoded to C'. However, DPL2 steers BOTH to L' AND C'.

[Sycho]

good job, must to have been lots of work, but, would you be able to post the setting you used for decoding the stream

[bleo]

DPL2 decoder: InterVideo EXP DMO filter
Settings (as per standard Movie mode):
- Expansion: On
- Algorithm: ProLogic2
- Autobalance: on
- Surround channel shelf filter: off
- Rs polarity inversion: off
- Panorama mode: off
- Output channel config: 3/2
- Dimension setting: 3
- Decode mode: movie/standard mode
- Center width control setting: 0 (no spreading)

[FuPP]

I know that DG has left. Any chance though this "4.8db matrix" will be incorporated into besweet ?

FuPP.

[bleo]

You mean into azid.dll?

In the mean time, you can modify and compile DSPguru's plugin http://dspguru.notrace.dk/BS_Downmix.zip.

Unfortunately I don't know how to compile. Any help?


buffer[j] =buffer[i++]; // fl. -> l.
buffer[j] +=buffer[i] * 0.70710678118654752440084436210485; // c. -3db -> l.
buffer[j+1] =buffer[i++]* 0.70710678118654752440084436210485; // c. -3dB -> r.
buffer[j+1]+=buffer[i++]; // fr. -> r.
buffer[j] +=buffer[i] *-0.86602540378443864676372317075294; // sl -1.2dB -> l.
buffer[j+1]+=buffer[i++]* 0.5; // sl -6dB -> r.
buffer[j] +=buffer[i] *-0.5; // sr -6dB -> l.
buffer[j+1]+=buffer[i++]* 0.86602540378443864676372317075294; // sr -1.2dB -> r.
// put LFE in here??
buffer[j] +=buffer[i] * 0.70710678118654752440084436210485; // lfe -3db -> l.
buffer[j+1]+=buffer[i++]* 0.70710678118654752440084436210485; // lfe -3dB -> r.

[frank]

DPL2 decoders are built with (analogue) operational amplifiers, and complicated control circuits. You'll never get the same results with simplified Software Direct Show Filters.

I don't trust InterVideo. I trust my ears and hardware DPL2 decoders in Pioneer or Kenwood receivers. And they decode the BeSweet generated DPL2 tracks very fine.

The channel separation of DPL2 cannot reach the quality of AC3 tracks because of their analogue characteristics.

What we need are some measurements on hardware decoders.

[FuPP]

@Frank
I have a hardware decoder (Onkio) but only my ears for measurements
:)

@Bleo
I thought it was in besweet (as I don't use BS downmix plugin) and I thought That Midas did not update Azid for a long time (far before DG incorporated DS2) :confused: But you are probably right !

Sorry, but can't help you for compiling...

Regards,
FuPP

[frank]

Yes, the DPL2 downmix is implemented in BeSweet, not in Azid.
Only DSPGuru can compile.

[Fr4nz]

Frank could you have a look at this thread in the hydrogenaudio forum? http://www.hydrogenaudio.org/index.php?showtopic=4639&st=0&#entry47454

In here it's stated that MP3 encodes badly surround informations altough in many other threads it's said that MP3 (LAME) preserves phase informations thanks to the safe joint stereo mode...anyway many people who have used LAME to encode movies AC3 audio in surround 1/2 says that lame is good also at --alt-preset 128 while others claim that only at high bitrates (for e.g. > --alt-preset insane(!!!)) Lame can reproduce surround informations decently. Could you clarify this point to me? Tnx!

ps: in my encoded soundtracks it quite good to me the --alt-preset standard for surround...

[bleo]

Yes! We do need measurements from hardware decoders, which is why I posted here!

I was about to post some predownmixed AC3 test files but had some trouble finding webspace :(

However, the downmix is easy to test if your receiver is connected to your computer. Just use AC3Filter and the custom downmix!

[/edit]Actually, are there any DVD movies out there that have a premastered DPL2 soundtrack and a DD 5.1 soundtrack? ;)

[FuPP]

if you have some short samples using normal matrix and 4.8 matrix, you could convert them to mp2 (bitrate = 192) and post them ; I will be able to burn them and test with my dvd player connected to the DPL2 receiver and tell you the result.

You are right though , I could do that myself using AC3filter and burn the result...

"are there any DVD movies out there that have a premastered DPL2 soundtrack and a DD 5.1 soundtrack".

A premastered DPL2 track from a DVD would not systematically be mixed from the 5.1 one, so I'm not convinced this is the best way to test and compare with one made using the 4.8dB matrix and a 5.1 track (I maybe did not get though...)

Cheers,
FuPP.

[Sycho]

I don't think there are any movies availble with a Dolby Surround Prologic II sound track, the only thing you can get readly avalible would probaly be GC PS2 XBOX games. there may be music discs out with DPL2

[Sycho]

Originally posted by bleo
DPL2 cannot steer 5 independent channels simultaneously. For example, during 22-24 sec, L contains 'LFE' and LFE contains [rumble]. Note, LFE is supposed to be decoded to C'. However, DPL2 steers BOTH to L' AND C'. [/B]
That is why dolby does not want the LFE included in the downmix

[bleo]

Very good lateral thinking sycho! I didn't even think about this when I wrote it! :rolleyes: So if I understand correctly, including LFE causes the sound field to collapse towards C'? :(

On the other hand, I don't want to miss out on those LFEs :p What to do? :confused: Yes I know DPL2 is already a huge compromise!

[Sycho]

just don't worry about it, unless the LFE has simaler information as the left or right channel, again, it will be confused. It is a lot simplier if there is no LFE, sometimes the decoder will just lock on the bass, and it will turn into a Dolby Surround decoder again.

If its an action movie, it is kinda iffy weather or not to keep the LFE
If its a comedy keep it
Muscial, I wound'nt use it (the decoder may get confused)
drama, again, kinda iffy
Horror, again, iffy

But in the end, the only real way to try would be trial and error

PS. when i'm watch DVD in my little cinema of mine, all my speakers are set to large and sometime (well lots of times) i forget to turn on my sub (which is only feed the LFE) it's not that much of a difference, exept my parents screaming

[Valex]

@bleo

Very good! I'll update AC3Filter's downmix matrix in the next version.

But however I think that real DPLII downmixer is little more complicated thing that just a passive matrix downmixer so I consider all this as just a simple hack. :).

I think that downmix coefficients depend on relative audio level in input channels. So it is needed to know coefficients as function of input levels:
Lt = L + 0.7 C + K1 * BL + K2 * BR
Rt = R + 0.7 C + K3 * BL + K4 * BR
where K1..K4 are functions of input levels.

To know this functions we need better to analyze encoder but not decoder.

Imagine that we have 2 signals at input: L with level lev_L and frequency f1 and BR with level lev_BR and frequency f2. After downmixing we have 2 signals Lt and Rt. Lt should contain f1 and f2 frequencies. Rt should contain only f2. We supposed that L level at output does not depends on anything (but we may be wrong), so f1 level in L should not depend on other channels level, but f2 level in Lt and Rt is nothing else that K2 and K4 coefficients! When changing f1 and f2 levels at input we can get K2 and K4 as functions K2(lev_L, lev_BR) and K4(lev_L, lev_BR) and then devise the total function!

I do not think that this functions are too complicated. It should be very simple. Somewhere at Dolby site I've read that DPLII encoder is rather simple thing but decoder is very complicated (it is why better to analyze the encoder).

@all
Anybody can make such a complicated experiment? :D

[bleo]

Yes this would be a good experiment! But of course, *IF* I could get my hands on a 'real' DPL2 encoder, finding out how it works should be easy! :D

Actually I don't think that a DPL2 encoder is complicated, except for the proper phase shifting rather than just phase inversion (?) I believe that the 'complication' arises because when mastering a 'real' DPL2 soundtrack, the producer in the studio has to monitor the downmix through a DPL2 encoder AND a DPL2 decoder (5:2:5 monitoring) and MANUALLY adjust the 5 input channel levels (NOT the downmix coefficients themselves) so that after all the matrixing and steering, the end result is to his liking.

So, without going to this trouble, I would be happy enough to use a "simple hack" constant passive matrix :)

One question: can we do these proper phase shifts?

[Valex]

I did not want to say that it is very complicated, I just wanted to say that it is not just a passive matrix. For example it may be something like CS encoding:
http://www.smartdev.com/CS-paper.html
(encoding system is at the bottom of this page, very simple...)

But of course, *IF* I could get my hands on a 'real' DPL2 encoder

Yes, it is a main problem.....

[Sycho]

Originally posted by bleo
One question: can we do these proper phase shifts?

theorecally: yes
easily: no

to do a 90 degree phase shif properly you need to take waht ever sound are going to be shifted and delay them by one 1/4 wave length of that sound, very hard to do for all frequences but it could be done on lets say anywhere from 1kHz - 4kHz and there should be not cancelation effect, the only reson for the phase shifts is, lets say you have 1.0 on the center channel and 1.0 total on the surround channels, well dump those through the downmix matrix (for simpicty dolby surround)

Lt = L(0) + 0.7071C(1) + 0.7071S(1) = 0.7071 - 0.7071 = 0
Rt = R(0) + 0.7071C(1) - 0.7071S(1) = 0.7071 + 0.7071 = 1

other than when you have the same thing on the centre and both suround you don't need a 90degree phase shift

but i know of no way of doing this on a computer except rendering the entire stream

PS. what some people do when doing there own dolby surround mixes is put a small delay in the sum of the surround going to the right channel and don't invert it ether

[Valex]

@sycho
90 degree phase shift can be done at the IDCT stage. As you know the compressed data is fourier-transfrmed. Phase shift in frequency domain is just a 'rotation' of all complex frequency coeffitients, that for 90 degree shift is just swap of real and imaginary parts. So if we do this before the inverse fourier transform we can make this phase shift in all-frequencies range easily and without any processing cost!

So the only problem is to direct myself to rewrite the IDCT code. :)...

[frank]

I've made some digital measurements with the updated DPL2 downmix matrix (tnx to bleo) using AC3filter (Valex) and DS filters from Cyberhome PowerDVD 5.0. certified by Dolby.

Results verified the new equals based on
The amount of acoustic power Ls in Lt is set to three times greater (+4.77 dB) than Rs.
Rear channel separation Ls/Rs: 1 kHz sinus, -29 dB (old matrix: -10 dB)

Dolby Pro Logic IILt = L + 0.7071*C - 0.8660*Ls - 0.5000*Rs Left-total
Rt = R + 0.7071*C + 0.5000*Ls + 0.8660*Rs Right-total

LFE = 0Longer terms are not nessecary.

Down scaling
1 + 0.7071 + 0.8660 + 0.5 = 3.073
All coefficients must be multiplied by 1/3.073 = 0.3254
Downwards scaling by -9.75 dB.

@DSPGuru
Please implement into BeSweet.

@Valex
Please debug the wrong downmix II parameters in AC3filter v0.70b.

[DSPguru]

so now you claim that the ratio between ls to rs should be sqrt(3) instead of sqrt(2) ?

i uploaded a new binary, let me know if it's okay..

[Fr4nz]

Frank did you use my AC3 to test the matrix????

I gave you the link via PM!

[frank]

@Fr4nz
I downloaded the soundtrack, many thanks!
At weekend I was sailing, no time... :)
And then I found the bug in AC3filter setup.
First measurements I made with sinus waves generated by CE pro.

@DSPguru
YES, like bleo stated.
Many 10x, I'll test it.

I have to make some more tests with pink noise.

Hint: Pink Floyd DVD 'The Wall' includes some nice AC3 test streams for loudspeaker adjustment.

[frank]

The new DPL2 parameters are now correctly installed in BeSweet 1.5b20. :)

Latest test results
(after expanding BeSweet encoded track with PowerDVD DPL2 filter to 3/2 wav - movie mode)

DPL2 channel separation (3/2)
Ls/Rs = 28 dB
Ls/L = 45 dB
Ls/C, Rs/C = 36 dB

If you decode DPL2 tracks on a normal DPL decoder the surround field is moving to front left or front right!

Channel separation on DPL decoder (3/1)
DPL2 encoded track (old par., 3 dB diff) Ls/L, Rs/R = 12 dB!!! :(
DPL2 encoded track (new par., 4.77 dB diff) Ls/L, Rs/R = 9 dB!!! :(

For movies:
Because of lower surround effects it's not recommended to encode DPL2 if you only have a normal ProLogic decoder (DVD player's DPL downmix).

If you want the AC-3 dialogue level unchanged then you have to apply a PreGain 10 dB (LFE = 0) in BeSweet.

[Fr4nz]

Frank I have one question: commercial DPL2 tracks (so encoded with commercial software) do have better surround effects on DPL systems than the ones we create with Besweet?

[frank]

I've never seen commercial DPL2 tracks on any media!
Maybe some game developers use it.

The first certified DPL2 software encoder comes from Minnetonka (6/2003), and is very expensive. There is a manual for the Surcode DPL2 encoder.

BeSweet's DPL2 downmix compromises movie mode.
We don't know more BECAUSE NO SPECS PUBLISHED!!!

How can a symmetrical DPL decoder separate DPL2? Because of the unsymmetrical rear levels in DPL2 there MUST be a leakage to the fronts.

In truth: Good compatibility exists upwards only! The DPL2 decoder has a DPL simulation mode.

New tests are welcome.

[Fr4nz]

Frank I have 1 little curiosity...are you Frank Klemm??? ;)
Anyway, as you said correctly, Besweet's DPL2 tracks doesn't sound good on DPL systems...luckily these work perfectly on DPL2 systems as you said, right?

[FuPP]

Originally posted by frank
If you want the AC-3 dialogue level unchanged then you have to apply a PreGain 10 dB (LFE = 0) in BeSweet. [/B]

Could you confirm that you mean to downmix LFE->L/R with 0dB "Gain" ?

Regards,
FuPP

[frank]

Oh no! You must SELECT the field in GUI and set LFE = 0, not LFE = 0 dB.
Look at Azid's downmix table.

@fr4nz
No I'm not that one.

[nuked]

"Because of the unsymmetrical rear levels in DPL2 there MUST be a leakage to the fronts."

Do you have some experience to back this up? I do not buy this argument without some testing at least. Of course a DPL I decoder can do no better than DPLI, but I'km not convinced it will do worse with DPLII material. SPEAKERS DON'T CANCEL. Do this test... play anything out of your mains only. Now plug the left into the left and plug the right into the left also but plug the right in backwards... or just use a mono radio source and plug the right in bacwards into it's usual plug. You will still hear sound and alot of it. I doubt you will notice a volume change at all even though the sound in the left and right is completely oposite polarity. It sounds more than a little strange.. like echoish or something(one reason why I don't make DPL encodes for stereo playback).. but still plenty loud, I'd be glad to explain why but just try it.

So symetrical or not doesn't change leakage to the front that much in DPLI. There is leakage in normal DPLI to the front, ALOT and there is leakage in DPLII played back on DPLI. I claim that DPLII played back on DPLI will at maintain some left-right separation for the rear sounds in the front speakers because as you say it's asymetrical... this is probably good. This may actually improve stereo compatibility playback significantly... something I'm curious about with teh new matrix anyway, and should provide at least a little left-to right separation for surround sounds even in DPLI playback even if the separation is generated from the front.


As for stereo compatibility. DPL has 2 goals... one to reproduce surround speakers on 2 analog channels but also to still sound good on stereo playback. I wonder what the new matirx does to the stereo playback... although I gave my conjecture above.

[frank]

Believe it or not, as you can read in my post all things were MEASURED and verified!!! :cool:

First test wav was a sinus multichannel track (1 kHz, -20 dB), and the second one pink noise (sound engineers are knowing that).
Encoded with BeSweet to DPL2, decoded digitally with latest Dolby certified DirectShow filter (Cyberlink Audio Effect, or Intervideo Audio Processor fx) to 3/2 multichannel wav.
If you switch to DPL decoding than the channel crosstalk from rear to front left/right is audible (9dB!!!).

The last audio test was made with the very good sound sample from Fr4nz. DPL2 encoded AND DPL decoded you realize that the rear left/right voices are moved to the sides because of leakage!

DPL2 decoded as stereo is compatible like DPL.

[Fr4nz]

Nuked the link for my AC3 test sample is: http://users.libero.it/i3ltt/Cazzate%20varie/prologe.AC3

[Fr4nz]

Originally posted by frank
The last audio test was made with the very good sound sample from Fr4nz. DPL2 encoded AND DPL decoded you realize no rear voice behind you, they are moved to the sides because of leakage!

I keep asking myself if this leakage would be avoided if using a commercial DPL2 encoder.

[frank]

Ha, then buy the Surcode DPL2 Encoder! :) :)

But I don't believe that they can prevent the crosstalk, the matrix math is known, no secret.
They can better manage the sound field directions, and levels for your own creations. But that is sufficently done in AC3.

[Fr4nz]

Originally posted by frank
Ha, then buy the Surcode DPL2 Encoder! :) :)

But I don't believe that they can prevent the crosstalk, the matrix math is known, no secret.
They can better manage the sound field directions, and levels for your own creations. But that is sufficently done in AC3.

Frank I was just guessing, no need to buy it :D
I'll stick with Besweet, you said that DPL2 encoded tracks play fine on DPL2 systems, so we don't have to worry ;)

EDIT: In internet I saw only Surcode's DTS encoders, not DPL2 encoders....

[frank]

Minnetonka Audio
http://www.minnetonkaaudio.com/news/2003/july/proII.html

[bleo]

@frank
What settings are you using for the CyberLink DPL2 decoder? Whenever I use it in GraphEdit, it seems to only do DPL1 decoding, that is, the surrounds are identical. :confused:

[frank]

Full version of PowerDVD 5.0 with multichannel support.
Graphedit, ...Cyberlink Audio Decoder, Cyberlink Audio Effect - "Using 6 speakers" - then you can select Pro Logic II and movie mode.
All as you wrote in your post.

The Cyberlink filter does not cut the first 2 seconds like Intervideo's does.

[Soulhunter]

Have found this (http://www.dolby.com/events/CEDIA/PLIIx/faq.html) info about Dolby Pro Logic IIx...

Maybe it's interesting for some PPL...!?! :)

Bye

[Fr4nz]

Hmm I don't think it is so interesting because it doesn't add nothing of new to our encoding techniques for DS2 :(

[frank]

How can a symmetrical DPL decoder separate DPL2? Because of the unsymmetrical rear levels in DPL2 there MUST be a leakage to the fronts.The DPL decoder can only recognize symmetric (180 deg phase shifted) parts of Lt,Rt as surround information.
From DPL2 remains 0.8660 - 0.500 = 0.3660 unsymmetric amount of Ls/Rs that cannot be removed from Lt,Rt, and so that amount is added to L,R.

DPL decoder feeded with DPL2 track
Crosstalk Ls/Rs into L/R
20 log 0.3660 = 8.7 dB, measured: 9 dB

for old DPL2 matrix
20 log (0.8165 - 0.5774) = 20 log 0.2391 = 12.4 dB, measured: 12 dB

[Fr4nz]

So the new matrix is better for backward compatibility but the leakage is inevitable, right?

[nuked]

"Encoded with BeSweet to DPL2, decoded digitally with latest Dolby certified DirectShow filter (Cyberlink Audio Effect, or Intervideo Audio Processor fx) to 3/2 multichannel wav.
If you switch to DPL decoding than the channel crosstalk from rear to front left/right is audible (9dB!!!)."


Frank, I don't doubt that at all, but does a DPLI encode with DPLI decode do much better? Not sure, just asking. This assymetry thing is interesting. I didn't say it would sound as good as a DPLII decode.. of course not, I just thouhgt it might sound as good as a DPLI encode.

Lets be clear... DPL does't really know anything about phase right? There is no DCT ivolved. It only knows polarity sometimes refered to as 180 degree phase which is not a perfectly acruate description of polarity when diferent sounds exist in diferent speakers. I used to think it just looks at L-R. From what you guys are saying it sounds like it looks at somethign a littel more complicated like
|L-R| - | |L|-|R| | wherer |R| means absolute value of R, which if I did that right is equivilant to saying 2 times which ever value is smaller if they are oposite in sign or zero if they are the same sign.
The added term is just the sort of non-antisymetric part. (edit:actually you have to mulitply the whole thing by L/|L| to maintain a sign) Wow.. does it really do somethign like that? I mean if you just do a simple L-R, even if R is zero and L is not... you still get a signal which would be sent to the back. That's how I thought DPLI worked, simple L-R. Of course if you try to remove the L-R signal from the front then you're left with a mono front sound along with your mono back sound... This isn't surprising cause you've just made a linear transformation from one two cordinate pair into another... hence why there's always a comprimise somewhere. I realize, as stated, real DPL decoders are more complicated than the simple matrices we aproximate with which is why I asked about testing.

edit:if this is what DPLI decoders should do, why don't we add it to our upmixing equations.. It means the matrix formalism of say matrixmixer would have to be abondoned... but no big deal.. these are not complicated equations to deal with... the ones I wrote here a probably kinda a retarded way to do it and maybe not the best.. but a first aproximation from how I visualized it off the top of my head.

[nuked]

As for stereo compatibility... I think people brush it off. If you just do volume tests with mics you'll probably find it's all reasonably compatible within a few db.. but the 180 polarity inverted sound makes your ears feel there is something being stolen from them. Do the little experiment I explained. You'll see what I mean imediately. Still I'll could believe one matrix is as compatible as another.

[Soulhunter]

@Fr4nz
Hmm I don't think it is so interesting because it doesn't add nothing of new to our encoding techniques for DS2

Uhmmmm... ???

Haven't posted it here, it was moved here... !!!

(Was originally posted in General Discussion :p)

Bye

[frank]

Nuked,
you should read carefully the papers about DPL published by Dolby. There you can find a lot of information about Pro Logic and adaptive matrix (by Roger Dressler).

The DPL decoder has voltage controlled amplifiers (VCA), feedback servo circuits to force the amounts of Lt,Rt feeding the S channel decoder need to be made equal.
The function of this servos is NOT shown in that simple matrix equations.
Much more complicated is the DPL II decoder. There each axis (Left-Right, Front-Back) operates independently.
That all is very difficult to understand if you don't have know-how in electronics. The developer Jim Fosgate (not Dolby) has 24 years experience in surround system design.

I didn't say DPL II sounds worse than DPL. I say that DPL II tracks on DPL decoders sound more like stereo because of leakage - NOT vice versa. That is a result of many many tests.
DPL tracks on DPL II decoders sound unchanged good or better!
For mixing of Dolby Surround tracks (input of inverted rear signals, signal cancellation, directions) there is a separate Dolby manual for sound engineers. Good downmixing is NOT a simple thing.

All we can do now is to generate test tracks, watching what the software decoders make to improve the downmix parameters.

[nuked]

yeah.. I totally agree it has to come from the tests. I realize these elctronics are complicated. I have enough electronics background to knwo I don't want to try to understand it in detail and I ahve perused the docs, also enough to knwo I don't want to un derstand it in detail. I mena I don't claim that my hand waving arguments are right by any means.. I just propose them as a counter logic if we're just gonna make hand waving arguments anyway. Tests are the key indeed.

There's also some fundamental ideas on information that apply though. One can prove with no understanding of electronics that any such tricks linear or non-lear, adaptive or not especially if they use little or no frequency info will fail miserably in some situations. Of course we all know that already and accept that it sounds pretty good none-the-less.

anyway... my question still is... does DPLII played on a DPL reciever sound worse than DPL played on a DPL reciever? I'm not sure but I don't think you've answered that directly. I may not have asked it well and I may not have understood the answer. In ohter words though will you ever really be worse off to make a DPLII encode than to make a DPLI encode.

[Fr4nz]

Nuked I played back DPL2 tracks made with Besweet on my DPL system. As Frank told you some posts ago there's leakage in right and left channels and the signal isn't so good on surrounds speakers. It's really better to stick with DPL1 encodings with DPL1 systems (strong and definite signals on surround speakers).

My question now is: would a commercial DPL2 encoder (like Minnetonka's one) make a better encoding than besweet?

Unfortunately I don't know where to get it (and so test it).

Maybe someone can get it?

[Sycho]

no matter how it is encoded the Dolby Surround Prologic II soundtrack will sound bad in prologic just becase the way the matrix was designed, buying a profession encoder will just yeild better panning from front to back or vice versa, this tread was started to try to tell the people of doom9 about the inproper downmix values and now it has turned into a debait about playing Dolby Surround Prologic II soundtrack on a Dolby Surround Prologic system. It all comes down to this, if you are using Dolby Surround or Dolby Surround Prologic use the "surround" downmix and nothing but, if you are using Dolby Surround Prologic II use only the "surround2" downmix and nothing else.