Distorted audio capture on linux.

[dezi]

The problem is in pkg/driver/microphone/microphone.go lines 133...

onRecvChunk := func(_, chunk []byte, framecount uint32) {
	select {
	case <-cancelCtx.Done():
	case m.chunkChan <- chunk:
	}
}

Callback function of malgo audio capture. The chunk buffer is send to channel.
Malgo will reuse the buffer while it is beeing processed.

You have to make a copy of chunk before sending it to the channel.

onRecvChunk := func(_, chunk []byte, framecount uint32) {
	newChunk := make([]byte, len(chunk))
	copy(newChunk, chunk)
	select {
	case <-cancelCtx.Done():
	case m.chunkChan <- newChunk:
	}
}

Please fix.
Regards,
dezi

[schrockwell]

I have the same problem, and I can confirm that this does partially fix the microphone driver. Where there was once a lot of distortion, there is now none! But unfortunately, the audio completely stops after a few seconds.

The audiotest driver works great.

• Hardware: Raspberry Pi 4
• OS: Ubuntu 20.04 Server
• Audio device: USB AUDIO CODEC

EDIT: I have tracked down the issue with audio stopping to something involving miniaudio or ALSA. I added a LogProc to the device, and found that the Stop callback was being called after the log statements:

[ALSA] poll() failed.
[ALSA] Dropping capture device...
[ALSA] Dropping capture device successful.
[ALSA] Preparing capture device...
[ALSA] Preparing capture device successful.

I could not get any more information on why poll() failed, except that this error is being raised from miniaudio.

I installed PulseAudio and ran the pulseaudio daemon so that miniaudio would pick that backend instead, and now it's working without any problems! (after the patch was applied above)

[kadharsh]

I faced the same problem of severely distorted audio, and this solution worked for me.
Initially, ALSA wasn't providing any audio output; although I could record audio using arecord, it wasn't being sent to the other side. After installing PulseAudio, the audio started working, but the quality remained heavily distorted. This fix by @dezi effectively resolved the distortion issue.

My hardware was a Rpi 4 running raspian os bookworm and a USB audio card

[Lien03]

I am also experiencing issues with distorted audio,
this worked for me.

• linux-imx 4.14.98
• USB Mic
• PulseAudio

thx

[kenzoi]

I had the same problem when using my bluetooth earbud some months ago, copy the buffer worked at that time.
(with a usb headphone it was working fine without any patch in the same pc).

But now it's working fine for me without any patch, I don't know if it was an update on my Fedora or on pion/mediadevices.

[dezi]

schrockwell: I have also experienced the

[ALSA] poll() failed.

Bug.

You will find my solution here:

mackron/miniaudio#836

Regards, dezi