Hello everyone.
I have been using CMedia USB sound devices to make laser control signals for many years.
I have sound devices with CM106L, CM6206 and CM6206-LX. Some are populated for 6 channels and some for 8.
The CM106L chip works perfectly. I can send it a stream of 16-bit data that uses the full range of -32767 to +32767 and at 100% volume in either alsamixer or Pulseaudio Volume Control, I get a perfect image.
https://laserboy.org/piDAC/perfect_circle.jpg
If I use a device with a CM6206, I get a very near perfect image (only clipped a tiny bit).
But If I use a CM6206-LX chip, it clips hard.
https://laserboy.org/piDAC/CM6206-LX_100.jpg
Even if I reduce the volume to 50%, it just seems to reduce the clipped signals.
https://laserboy.org/piDAC/CM6206-LX_50.jpg
I'm not sure what is going on here, but it seems like there is some kind of internal digital gain of more than 1.0.
I also notice that lsusb shows exactly the same device ID for both the CM6206 and the CM6206-LX.
.... 0d8c:0102 C-Media Electronics, Inc. CM106 Like Sound Device
And what's really weird is that a genuine CM106L shows up as something else!
.... 0d8c:0006 C-Media Electronics, Inc. Storm HP-USB500 5.1 Headset
Is there something I can do in alsa config to fix this issue?
The CM106L is long since out of production and it seems like any device that uses the CM6206 might have the LX version (or not). There's no way to know until I get them and open them up.
I'm using this on an Orange Pi Zero 3 4gb running dietpi with the 6.6.16-current-sunxi64 kernel, but that doesn't seem to matter. I get the same results any other way I try it. The LX version of this chip clips the same way in Windows too!
Thanks for your time.
James.