[AudioI] Octo inconsistent (usually fails) behavior with arecord | aplay

[Matt Flax]

On 14/12/21 4:37 am, Matt Onderlinde via People wrote:
> Hello,
>
> I got the Octo and am trying to pipe the result of arecord to aplay like this:
>
> arecord -f cd - | aplay -
>
> (I've tried numerous other variations of this command...)
>
> This works maybe 5-10% of the time... but even when it works it
> eventually fails (with no error messages and in the terminal it
> appears like it's still working) and stops playing output. It doesn't
> seem to matter what the system load is either on the pi.


I assume that it is to do with channel swapping. Most likely due to 
asynchronous behaviour in this case.

Does the gtkIOStream fullduplex test work ? 
https://github.com/flatmax/gtkiostream/blob/master/test/ALSAFullDuplexTest.C


>
> arecord -f cd - > /tmp/tmp.wav seems to always work... so something
> about piping arecord to aplay doesn't seem to work.
>
> Also, on reboots the card is only recognized about 30% of the time. I
> actually bought a 2nd card suspecting the first one might have a
> hardware issue but I get the same behavior with the 2nd card.
>
> I can always get it working with this:
>
> sudo modprobe -r snd_soc_audioinjector_octo_soundcard
> sudo modprobe -r snd_soc_cs42xx8_i2c
> sudo modprobe -r snd_soc_cs42xx8
> sudo modprobe snd_soc_cs42xx8
> sudo modprobe snd_soc_cs42xx8_i2c
> sudo modprobe snd_soc_audioinjector_octo_soundcard


Not sure what that is due to, strange behavior.


>
> For the ~/.asoundrc I'm just using the out-of-the-box file that comes
> with the .deb file from github.
>
> I've also tested in Audacity and see that sometimes the channels
> record and sometimes they don't... it's just inconsistent.

Again possibly due to channels swapping ?


>
> My pi is the Raspberry Pi 3 - Model B and I've tried both a 2.5 and 3
> amp power supply. I've also tried several Raspbian versions including
> the latest Buster release as well as some of the releases from 2017
> when the .deb file and this project was really getting going.
>
> My project goal is to record from up to 6 microphones at once and
> merge them into a single output channel that goes into a GoPro camera.
> So far I can't even get to the merging step since arecord | aplay is
> so unreliable.


Regarding recording, it is 100% reliable to undo any form of channel 
swapping. Here is some sample code to demonstrate :

https://github.com/flatmax/gtkiostream/blob/master/test/ALSAFullDuplexMinScan.C#L49-L88

Basically the way it works is that 2 of the 8 input channels always have 
the same value ALWAYS! So we detect those channels and we know they are 
always channels 7 and 8. We then circularly shift the columns (channels) 
to their correct positions in the audio data matrix and we never 
experience channel swapping.

That should serve your project. You could create an ALSA external plugin 
to perform this process and record from that plugin if you like.

To help others ...

What I would like someone to do is work out whether the output channels 
are equally shifted as the input channels. If so, then both problems are 
solved.

I have worked with a student in China who was doing 16 bit recording and 
playback. They managed to get a 16 bit version working reliably for 
input and output.

Matt


> Any help would be much appreciated!!!
>
> Thanks,
>
> Matt
>
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