[rbp] Apply volume control at audio_mixer when possible #2081
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
On Pi, the analogue audio has ~10 bits so it is important to make use of the full dynamic range.
Currently when downmixing from, say, 5.1 to stereo the "boost volume on downmix" is applied to mixer component. The volume is applied after this.
If you don't boost volume on downmix you reduce volume level, and so lose dynamic range.
If you do boost volume on downmix you risk clipping and distorting audio. The volume control happens too late to avoid this.
This patch applies the volume control to the downmix coefficient which allows "boost" to be enabled, and the volume to be adjusted to maximise range without clipping.
See huceke/omxplayer#58 for original discussion for a similar patch to omxplayer. Thanks to torarin for original patch.