Here's my solution with an OS based on RaspiOS Bullseye (with kernel 6.1).

A quick way to check if the inputs are saturated by noise:

$ arecord -c 6 -f S24_LE -V mono -r 96000 /dev/null
Recording WAVE '/dev/null' : Signed 24 bit Little Endian, Rate 96000 Hz, Channels 6
##################################################+| MAX

In my case, the result is the same with all combinations of number of channels, sample resolution, sampling rate, and input levels.

Because the Linux images included in the RaspiOS distributions (that can be installed from apt) are missing the required overlays, I installed a Linux kernel version 5 made specifically for the RPI: https://github.com/kdoren/linux/wiki

I installed the arm64 PREMPT_RT version because it prefer it for audio, but it's not required.

Then I tuned the OS for audio with help from this script: https://pypi.org/project/rtcqs/

Here's more tuning info, specifically for the RPI: https://wiki.linuxaudio.org/wiki/raspberrypi

The above arecord command will show a VU meter that momentarily go up to MAX, then it quickly go down to 0%; this is a known issue when initializing the Octo for recording. When using a sound server like Jack, the inputs of the Octo are initialized when the server starts, so that could be a way to avoid spikes when recording from jack.

I hope it helps (until the issue is solved for kernel 6).

Marc

Hi Marc,

yes, I can try the suggested kernel.

thanks.

 

Fabricio 

On Wed, Jul 12, 2023, 08:51 Marc Lavallée via People <people@lists.audioinjector.net> wrote:

Le 2023-07-12 à 07 h 42, I wrote :

> Hi Fabricio,
>
> Can you try with an earlier OS using a kernel version 5.10+, for
> example one based on Debian Buster?
>
> https://downloads.raspberrypi.org/raspios_armhf/images/raspios_armhf-2021-11-08/
>
Oops! The link I sent for the OS based on Bullseye, here's the link for
the OS based on Buster (with kernel 5.10+):

https://downloads.raspberrypi.org/raspios_armhf/images/raspios_armhf-2021-05-28/

Marc

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