What could happen when using DPLII downmix on a stereo source?

[Chainmax]

I figure it basically does nothing and just implies unnecessary work. Is that a correct assumption?

[ursamtl]

DPLII is designed to be compatible with regular stereo playback. I have noticed that they sometimes seem to have a slightly wider, less focused stereo image, almost like having a stereo wide control turned to about 120% width.

[Chainmax]

Maybe I phrased myself wrong. What I meant is that generally DPLII downmix is used to convert from 5.1 to 2.0. What happens if the source is already 2.0 and I use azid with the -s dplii option?

[ursamtl]

Ok, sorry I can't help you with that one.

[tebasuna51]

Just is ignored without unnecessary work.

[Chainmax]

I see, thanks for the answer :).

[Ac3Dc3]

using a specific example, would a 5.1 ac3 file containing audio in the FL and FR channels, but digital silence in the other four, be converted to a stereo file with those exact channels (and the others discarded)?

[tebasuna51]

Any downmix matrix (stereo, dpl, dpl II) guarantee a proportional output to the FL-FR input if the rest of channels are silence.

A exact output can be obtained using AviSynth:
a=NicAc3Source("input_5_1.ac3")
fl=GetChannel(a, 1)
fr=GetChannel(a, 2)
MergeChannels(fl, fr)

[Ac3Dc3]

OK, thanks tebasuna51

i don't seem to be able to get a valid stereo output using that script with a certain ac3 file. do you mind taking a look at it? i have PM'd you a download link

[tebasuna51]

1) The methods I know are always based in decode the ac3 stream. If you want any lossy encoded, output never can be exact. I don't know any method to convert a 5.1 ac3 in 2.0 without reencode.

2) I need know the final output you want. A uncompressed file (wav), reencode to ac3 or other format?

3) You need automate the process, is a occasional job? What audio software you can use?

For instance, I decoded your sample with Azid.exe then I have a multichannel wav file. I see in Audacity the 6 channels and in fact all are empty but FL-FR. I use wav2stereo.exe (WaveWizard can do the job also) to obtain three stereo wav's: FLFR, CLFE and SLSR from the 6_channel_wav, the FLFR is your desired output.

To use the AviSynth method you need AviSynth 2.5.6, .NET FrameWork v2.0, the AviSynth plugin NicAudio.dll and Bepipe.exe.

[Ac3Dc3]

1 - Thats fine, I'm not trying to keep it as ac3 anyhow.

2 - I'm trying to encode to aac.

3 - Using neroaacenc.

Yeah, I have split up the channels before and that's what I get too. The problem is, I'm trying to go from the ac3 to aac via avisynth.

Using this:
mySource=NicAC3Source("C:\audio.sample.ac3")
fl=GetChannel(mySource, 1)
fr=GetChannel(mySource, 2)
MergeChannels(fl, fr)returns two channels but they are silent. FYI, I'm using NicAudio_alpha3.

Do you know why?

[jmac698]

I'm sure there is a way to losslessly convert 5.1 to 2.0, but I can't remember where I saw that.. ah, maybe projectx..

[tebasuna51]

returns two channels but they are silent. FYI, I'm using NicAudio_alpha3.

Do you know why?
Problem found.

Your sample have only the two first frames 5.1 (64 ms.), the rest is 2.0, then NicAc3Source create a wav 6 chan but replace with silence all the frames 2.0.

The solution is cut the first two erroneous frames for instance with DelayCut.