Implementing Dolby Prologic I/II Decoder

[hypercube]

does any one known where I can found some technical information
to implement dolby surround DECODER in my software ?

please don't say "www.dolby.com", there is nothing there.
naturally.:rolleyes:

[frank]

There is enough stuff.
Dolby Technical Information (http://www.dolby.com/tech/#head2)

Simple way is to use BeSweet.dll.

[hypercube]

this is incredible. Everytime I'm talking about
dolby stereo decoding, people say "see BeSweet"

:rolleyes:

BeSweet is a pseudo-dolby stereo ENCODER. not DECODER !

Here some informations:

There is one encoding scheme: Dolby Stereo
There is 3 decoding schemes:
Dolby Surround: Passive Decoder
Dolby Prologic I: Passive Decoder followed by Active Matrix
Dolby Prologic II: Passive Decoder followed by better Active Matrix

The encoding equations can be found everywhere in free source code...

But decoding equations....:(

[frank]

What do you want to decode?
2/0 DPL or DPL2 encoded stereo tracks? Every good software player has it!! :rolleyes:

Into 5 separated channels? Then you'll need a 5.1 sound card.
On-board 5.1 sound chip is not worth that work, believe me. Too much noise, a 5-wire link to the amp...

DPL:
Only passive matrix equations are simple:
L = Lt, R = Rt, S = Lt - Rt
But channel separation (3 dB), crosstalk is too bad.

Pro Logic needs more:
- active matrix for better channel separation,
- 15-40ms delay in the surround channel
- dolby noise decompression in the surround channel
- 7 kHz low pass filter in the surround channel
No linear equations for Pro Logic.

DPL2:
Forget it. Too much complicated and not published.

There are no simple decoding equations because of feedback-loops and time delays, frequency filters... realized in anlogue circuits or a lot of DSP modules.
The only solution is using the Direct Show audio filter of a software player like PowerDVD or WinDVD. They are Dolby licensed.

[hypercube]

for pro logic, I can make 15-40ms delay and 7 kHz low pass filter in the surround channel.
But as you say, crosstalk will be terrific

so... I give up this funky idea ! :p

[ux-3]

@frank:
The sound card issue caught my attention. I am not sure but I think no standard soundcard in the < 100$ range can deliver a dpl2 surround decode on 5 channels digitally. From my SB Live! I've learned that anything but ac-3 will be only two channels if using the digital output. To my knowledge, if I want to use 5.1 on games or other decoded stuff, I have to run the 5 wires to my amp. I would be more than happy to be corrected on this one...

[hypercube]

Decoding prologic II should be possible using DirectShow filters from WinDVD 4 !!

First with Dolby Digital AC3:
Using Graphedit, I made some test:

AC3 file => AC3 PARSER => Intervideo Audio decoder
=> Intervideo Audio processor => WAV DEST => WAV FILE

check 6 Speakers in Intervideo Audio processor
The WAV FILE is Stereo, but in fact contain all channels samples.
(this only mean WAV DEST filter don't recognize properly 6 channels
as input, WAV DEST source code is public so it's not a problem...)


The Intervideo EXP DMO section contain
3 algorithm setup:
ICE, Prologic and Prologic II.
only ICE is enabled. this is the problem.

all other stuff should be resolved by programming.

[frank]

@ux-3
I didn't say digitally. With PowerDVD XP 4 Deluxe you get all you need. I have a P4 with onboard 5.1 sound chip. PowerDVD decodes AC-3 tracks to DPL2 and the chip outputs to 3/2 analogue! :)
But it's a horrible sound because of too much digital noise.
Thats why I say onboard 5.1 dec is BS...

Yes, SPDIF 5.1 output makes trouble, especially when the tracks aren't AC3. I think that is license politics.

@hypercube
As I said the only way is using Direct Show from players. :)
Search the forum, I remember that some guys had success with Graphedit and DirectSound Device.

[hypercube]

winDVD must be registered to use dolby prologic decoding.
after doing some stuff (you know what I mean :D ) my
test work perfectly with graphedit.

I'm planning to convert Old Dolby Surround DVD (like Bladerunner)
to SVCD with MPEG Multichannels.

This is usefull because I don't have any dolby surround decoder.
My 762 Phillips DVD player decode only Dolby Digital.

[ux-3]

Frank: I got the impression that you considered it possible from your comment on the 5 wire link. It sounded to me as if you suggested a soundcard without that five wire link. Hence I thought that you meant a pci Soundcard connected digitally (how else). And I would love to get that done, but all my readings came down to: Just Stereo or AC3.
Hope this helps straighten things out...

Originally posted by frank
Into 5 separated channels? Then you'll need a 5.1 sound card.
On-board 5.1 sound chip is not worth that work, believe me. Too much noise, a 5-wire link to the amp...

[frank]

@hypercube
Some months ago I owned a 762. And this player is able to play Multichannel MPEG-2 audio from SVCD! Via digital link too!
I linked it to my receiver Pioneer VSX-859RDS and worked fine.

@ux-3
I have a 5.1 on-board chip on my motherboard, and I could play DS2 tracks with PowerDVD only analogue. Because of noise from digital chips it sounded horrible.
The analogue 5.1 connection is a poor man's solution. What would be the next? 7.1 cables for surrround EX??
The best multichannel solution is a digital/optical link. Followed by high-tech audio equipment. I never watch quality sound on a noisy PC.
And some day the programmers have the drivers we needed :)

[E-Male]

Originally posted by hypercube
after doing some stuff (you know what I mean :D ) my
test work perfectly with graphedit.

and how did you do the output to a file?

[ux-3]

@frank:
When I was shopping for a 5.1 card, I was thinking it would output dolby digital and could be connected to any such receiver. Man, was I surprised when I learned that it wouldn't work this way at all, unless the card was just piping it through. I really thought a modern soundchip could encode a given 5.1 signal to AC3 in realtime. Oh well, we are all used to getting new cards every other year...

[MaTTeR]

Originally posted by ux-3
I really thought a modern soundchip could encode a given 5.1 signal to AC3 in realtime.

AFAIK the only one able to pull this off so far is Nvidia with the nForce mobo boards. I'm hoping to get one soon myself and try piping a 5.1 Vorbis file to it. I know of no sound cards able to do this though.

[hypercube]

@franck
762 is a good player. skip sometimes but image quality is very good.
this is strange that Phillips didn't put the MPEG Mutlichannel logo on it...

@E-Male
use File Writer directshow filter.

@ux-3,MaTTeR
subject of this thread is "Implementing Dolby Prologic I/II Decoder"
:-)

[E-Male]

ok, i´ll tyr as soon as i gind time

I´d need this upmix to add deleted scenes with 2.0 audio to a 5.1 audio movie

just one more question, what result does the filewriter produce??
6ch wave, ac3files, ...?

cu
e-male

[hypercube]

output is 2 channel PCM WAV: BUT, ALL channels are here !
(interlaced)
you have to make some programming stuff to extract
properly the audio data...