Open Sound System driver for CMedia Electronics CMI8738/8768 audio

CMI87xx device characteristics:

  • 8/16 bit playback/record

  • mono/stereo/4ch/5.1ch playback

  • 8KHz to 48Khz sample rate.


The CMedia chip provides some unique features that are set up by the Mixer chip. Running ossxmix will display the CMI8738 mixer panel.

Most of the sliders and buttons are self evident. However there are some options that need explaining:

Dual Dac: Enabling this button sets the CMPCI device as two separate output devices with /dev/dsp1 audio going to the front and /dev/dsp0 going to the rear outputs. Separate audio streams can be send to the device simultaneously.

Speaker Mode: The audio can be sent just to the front speakers or it can be sent simultaneously to all speakers in the "Spread" mode.

AC3 passthrough only works on Models 037 and higher. This is because of a hardware bug in the earlier models so check the model number (ossinfo -a).


  • Enable will enable SPDIF output.

  • Rec will allow you to record from the SPDIF device. Note that when you have SPDIF recording enabled, you cannot play 4/6 channel audio.

  • Polarity - certain models require you to flip the bit otherwise you get distorted audio.

  • IMon - monitor input via SPDIF in.

  • Optical - sets the SPDIF to Optical (TOSLINK) or RCA Jacks interface.




/etc/oss4/conf/oss_cmpci.conf Device configuration file


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