Graphics, sound and multimedia • USB audio CM106, CM6206, CM6206LX

Hi everyone.

Probably the most readily available multichannel USB audio devices all seem to be based on these CMedia chips.

I have examples of each chip on a sound device. Some are populated for 8 channels and some for 6.

If I plug in the original CM106, it works perfectly.

If I plug in a device with the CM6206, it works almost perfectly.

If I plug in a CM6206-LX, it clips hard.

When I reduce the device volume using either alsamixer or Pulseaudio Volume Control, it is still quite distorted.

I'm not exactly sure what this means, but it seems like there is some internal digital gain of more than 1.0 inside the DAC. Setting the volume in software just seems to attenuate the clipped signals.

I'm using the DAC to control a laser projector. These circles are made in my app (LaserBoy) and use the full swing of 16-bit signed int (-32767 to +32767).

If I simply reduce the size of the circle to not swing to the rails, it's fine. But that is not a good solution.

This is an image of what is supposed to be a perfect circle at 100% volume (CM6206-LX).
https://laserboy.org/piDAC/CM6206-LX_100.jpg

This is 50% volume (CM6206-LX).
https://laserboy.org/piDAC/CM6206-LX_50.jpg

This is 100% volume with the CM106L
https://laserboy.org/piDAC/perfect_circle.jpg

Is there something I can do in alsa config, Pulseaudio, or Pipewire to fix this issue?

Thanks.

James.

Statistics: Posted by JamesLehman — Fri Apr 19, 2024 6:21 pm — Replies 0 — Views 34

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