support phase shift for Dolby Pro Logic II / Dolby matrix downmix
|Reported by:||AndreG||Owned by:|
|Blocking:||Reproduced by developer:||no|
|Analyzed by developer:||no|
Summary of the bug:
Hello guys. I am trying to downmix a 5.1 audio to 2.0 (stereo) using the audio resampler filter "matrix_encoding=dplii". The resulting stereo audio presents some audio level bias towards the right speaker when there is more than one active channel on the surround stream. That is, it seems that the audio volume on the right speaker is higher than it should be. This is, of course, using a test signal where all surround channels produce the same sound at the same volume.
How to reproduce:
% ffmpeg -i ChID-BLITS-EBU-Narration441-16b.wav -ac 2 -filter:a "aresample=matrix_encoding=dplii" dplii.wav ffmpeg version 2.4.4 Copyright (c) 2000-2014 the FFmpeg developers built on Dec 4 2014 14:13:11 with Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
You may freely obtain the surround test file I used on the command above from Fraunhoffer's website.
Direct link to the surround wave file: https://www2.iis.fraunhofer.de/AAC/ChID-BLITS-EBU-Narration441-16b.wav
Fraunhoffer's page where that file's URL is located: https://www2.iis.fraunhofer.de/AAC/multichannel.html
If you analyze both the surround input file and the resulting stereo wave file on Audacity, for example, you will notice that by 19 seconds into the audio stream all channels are active with a test signal. The same point in time on the resulting DPL-II downmixed shows a "higher volume" on the right speaker. This effect is even more noticeable by 22 seconds when they change the test signal. It is interesting to note that in the initial seconds of the file, when a male's voice is announcing each channel individually, I could not notice this right speaker bias. The channel downmixing in that segment sounds correct. This effect is very noticeable on sound tracks with very active surround channels, they all seem to be stronger on the right speaker.
Change History (12)
comment:7 by , 9 years ago
|Summary:||Dolby Pro Logic II / Dolby matrix downmixing level balance → support phase shift for Dolby Pro Logic II / Dolby matrix downmix|
|Type:||defect → enhancement|