CTAG face2|4: A Linux-Based Low-Latency Multichannel Audio System

Please note: These might not be the devices you are looking for when searching for the CTAG capes for BeagleBone. You will find them at FACE and BEAST multichannel audio capes by CTAG and Bela.



  • 2 stereo ADCs and 4 stereo DACs
  • Up to 96 kHz sampling rate with 8 audio channels (up to 192 kHz with 4 channels)
  • 24 Bit word width
  • Separate interfaces to ADCs and DACs
  • Asynchronous sampling rates for playback and capture
  • Up to 3,2 ms round-trip-time
  • Mobile usage (the BeagleBone Green and the audio card both are supplied with 5V supply voltage)


  • The sound card is based on the AD1938 audio codec with 2 stereo ADCs and 4 stereo DACs of Analog Devices Inc. and was designed by CTAG Fachhochschule Kiel.
  • To control and use the sound card via I2S and SPI the BeagleBone Green was used due to its Multichannel Audio Serial Port (McASP) of the AM335X SoC, which supports up to 16 audio channels on a single data line.

Project Components / Source Locations

  • CTAG face 2|4 at Github, I2S sound card based on AD1938 audio codec by Analog Devices Inc. (repo contains hardware design files, help documents and device tree overlays)
  • BeagleBoard Linux, drivers (merged in official kernel) are compatible with BeagleBone Black/Green and BeagleBoard-X15
  • Linux driver development repository, development of driver for daisy chained codecs and software SPI
  • Adapter card “bbg-cape” to connect the BeagleBone Black/Green with I2S sound card, see Github repo above
  • Adapter card “con-cape” with stereo jacks and headphone amplifier, not yet published due to some bugs
  • BASH script for automatic evaluation of latency, THD+N, DNR, crosstalk and frequency response using GNU Octave
  • libdsp-x15, DSP audio library for BeagleBoard-X15 (C66x DSPs, integrated in AM5728 SoC)
  • Surround-Delay Demo Audio Effect
  • Debian Wheezy SD card image for BeagleBone Green (evaluation script and demonstration effect is included)
  • Documentation / Thesis (German)


  • Mobile sound studio (simultaneously record several inputs with different audio effects applied and preview them on different outputs in real time)
  • Effect device for various music instruments
  • Open platform for DIY audio projects
  • DIY Eurorack modules
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