[BUG] Distortion on the second pipeline connected to demux

[bardliao]

Describe the bug
Distortion can be seen on the second amp output with #2526 applied

To Reproduce

1. run aplay
2. listen to the output from both amps

Reproduction Rate
100%

Expected behavior
Clear output from both amps

Impact
annoyance

Environment

1. Branch name and commit hash of the 2 repositories: sof (firmware/topology) and linux (kernel driver).
   • Kernel: topic/sof-dev branch thesofproject/linux@d05959d + ASoC: SOF: topology: fix: handle DAI widget connections properly with multiple CPU DAI's linux#1863
   • SOF: master branch thesofproject/linux@d05959d + [RFC] Topology for synchronize playback #2526
2. Name of the topology file
   • Topology: sof-cml-rt711-rt1308-rt715.tplg
3. Name of the platform(s) on which the bug is observed.
   • Platform: CML laptop with 2 rt1308s

Screenshots or console output
sof-logger-distortion.txt

[bardliao]

@slawblauciak I know the sof-log log is not sufficient for the audio quality issue. But can you check if you can find anything wrong with the sof-log log? In the meantime, I will try to do loopback to capture the audio data for you.

[bardliao]

@slawblauciak I did a loopback test today, and I can get the same distortion as what I hear. An interesting thing is that the sound is very clear when I test it with a 1K tone.
Below are the recording file captured by loopback. The first picture is 1k tone and the second one is a voice says left channel and right channel repeatedly.

I also upload the captured wav here

1k.zip
lr.zip

Could you look into it?

[slawblauciak]

I'm on it. Can you also reproduce the issue by generating some other tone? Like 1.5K? Or 2K?

[bardliao]

@slawblauciak That is the result of testing with your testing file.

sine.zip

[bardliao]

@slawblauciak The distortion is gone if I revert #2541. I also tried adding a PGA to the second DAI, and the distortion happens. So, what I observed is the distortion will happen if a PGA on the second pipeline. In other words, the second pipeline can only work with pass through pipeline.

[bardliao]

I also don't observe distortion if I play a 32bits wav no matter if a PGA on the second pipeline or not. @RanderWang Do you have any comments?

[slawblauciak]

@bardliao looking at the #2541: I don't really understand why it was like that to begin with. Why apply volume to only one of the demux outputs. It is an interesting finding tho, it's very strange.

[bardliao]

@bardliao looking at the #2541: I don't really understand why it was like that to begin with. Why apply volume to only one of the demux outputs. It is an interesting finding tho, it's very strange.

@slawblauciak The reason of #2541 is that I want to keep the same volume level for two pipelines. @RanderWang said he think the issue probably due to bad format conversion. ie, convert 16/24 bits to 32 bits see https://github.com/thesofproject/sof/blob/master/src/audio/dai.c#L769.

[slawblauciak]

I think there's a problem with stream param propagation, also why you had to do that hack with the 2 channels. So, I think it might all be related. I'm currently investigating that.