Released: DolbyProLogicII decoder that works! (proper channel separation)

[3dsnar]

With the new release of Aud-X (v. 1.2) we have lounched a DPLII decoder. I spent tens of hours in Matlab to figure out how to spearate all the channels properly, so I hope you will like the result.

In general (I think - please correct me if I'm wrong) there is no proper free software DPLII decoder available (i.e. the channels separation is not performed correctly). And Dolby does not publish anything on the decoding issue. Thus it is a bit
mysterious topic...
Therefore, I hope that our DPLII dec. algorithm will be of use for you.

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I was able to test the results on me, my wife and my friends and it seemed to be similarly effective, in terms of channel separation, as the original, hardware Dolby decoder.
All the tests were perfomed on the same HT amp.
Interestingly, they claimed that my algo sounds better in terms of linear distortions (the test noise played with the original DPLII decoder seemed to have distorted frequency characteristics...), but everyone must judge by his/her own...
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But, ofcourse opinion of all possible users is very interesting for me, so I could use some suggestions to improve this algo.
Here is a test sound for ya (maybe it will be useful).
http://forum.videohelp.com/images/guides/p1481457/speech6chtest_dplii_dwmx.rar
or check the attachement
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Just in case (probably for most readers this is more than obvious ), here are some details how to test the algorithm
and compare it to other existing ones.

To perform a comparison with the use of external hardware home theatre system, please do the following:
1) Select in Aud-X DS filter config PCM stream compatibility.
2) Select in Aud-X DS filter config SPDiF output. The decoded (to 5.1) stream will be encoded to AC3 (448 kbps), and sent to the external amp. And you will be able to listen to the results of our algorithm
3) Select stereo output in Aud-X filter to send the original stereo (DPLII downmix) to the external amp.
4) Select (in your amp) DPLII decoder.
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To perform a comparison with the use of other DS filters (e.g. FFDshow), please do the following:
1) To use other filters, please disable Aud-X (or disable PCM stream compatibility), and select the appropriate decoding option in the compared filter.
2) Enable PCM stream compatibility and use Aud-X 5.1 output
to decode the input DPLII downmix. Please make sure that the input stream is not already decoded to 6 channels by other filters, preceding Aud-X (there is an info in our decoder filter on the number of channels, or the type of the incoming stream).

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The channel order in the test file is
1) FL
2) FR
3) C
4) SL
5) SR

 

[kyleb]

Seperation works nicely on my system but sound quality was rather rough. The test file you linked played back well for the most part but took a moment to kick in; as in instead of "front left" I heard "ont left" or sometimes even just "left." Playing back more complex content from a DVD with WMC caused a lot studers in the sound and trouble resuming playback after pausing, and even when not studering there was a tin-ish low bitrate like effect most noteable vocals. Also, using the decoder, playback was also excessively loud compared to any other sound source I've used.

Relevent portions of my setup:

A64 @ 2.2ghz
2gb pc3200
Audigy 2zs with their OpenAL beta driver
Denon AVR-2805

 

[3dsnar]

Hmm, sounds like direct show filter chain problems...
What filter did you use for decoding the audio stream?
What stream was it?

 

[kyleb]

I'm sorry, I previously typed WMC when I meant MPC and I didn't realize it at the time but I see now and remember that I disabled MPC's internal decoder a few weeks back so it was using the Cyberlink decoder from ATI. Reverting to MPC's internal decoder resolved the resuming playback issue as well as most of the studdering issues, but some cutting in and out remained and occasional tin-ish sound and distortion croped up with complex audio as well.

Also, source I orignaly chose for testing at first was probably a near-worst case senerio as it has a lot of varition of both in the music itself and the directional cues within it; it's A Perfect Circle's "Counting Bodies Like Sheep to the Rhythm of the War Drums" off their aMotion DVD. I tried a few other DVDs and while they did skip a bit using the Cyberlink/ATI decoder, the MPC decoder only did the studdering on a few tracks off the aformentioned DVD with the one track noted above being by far the worst.

 

[3dsnar]

OK, I am glad that the studdering problem stopped.
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Regarding the DPLII decoder issue:
Well, this is just a prologic decoder, and by definition it will never be as good as a proper digital multichannel standard. Simply, compare the results to dolby licenced algorithm
(available in PowerDVD for example) and you will see that it sounds even a bit better
(this is a subjective thing, so you must do your own listening test).
General, if you want to achieve multichannel sound at low bitrate with high quality,
please use Aud-X for encoding.

 

[kyleb]

The studdering isn't gone when switching to MPC's internal decoder, it's just lessened to effecting only a few situations I tested instead of happing with everything I tested like it did when I was using Cyberlink/ATI decoder.

As for the distortion I mentioned, I wasn't comparing to digital surroundsound but rather 2-channel output expaned by my receiver.

 

[3dsnar]

PowerDVD theoretically should have the same DPLII decoding algorithm as your hardware (since both are provided by Dolby Labs).
I was testing on both, and results were very much comparable to Aud-X DSfilter DPLII decoder. But ofcourse, this is my (and few others') subjective opinion.

Thanx very much for all the tests :smile: