Cape4all: A multi-channel audio interface board for BeagleBone

About Cape4all

The Cape4all system is based on the Beaglebone Black or Beaglebone Black wireless single-board computer. A multi-channel audio interface board is provided as a “cape” for the BeagleBone Black. Its hardware design is available under an open-source license on Github and was developed by the Leibniz University Hannover in the Cluster of Excellence “Hearing4all” with a focus on low-latency multi-channel audio capabilities. In collaboration with Daniel James and Chris Obbard from 64Studio an ALSA sound driver was developed and a Linux system was optimized for low-latency, real-time audio processing with openMHA: Mahalia.

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Block diagram with three codecs and 6 input channels. (source)


At the heart of the Audio Extension Board, there are three ADAU1761 low-power codecs from Analog Devices interconnected with the Sitara Multichannel Audio Serial Port (McASP) using a 3-input logic OR-Gate. The ADAU1761 is a SigmaDSP Stereo, Low Power, 96 kHz, 24-Bit Audio Codec with Integrated PLL.

ADAU1761 features

Each of the three codecs provides the following features:

  • 24-bit stereo audio ADC and DAC: >98 dB SNR
  • Sampling rates from 8 kHz to 96 kHz
  • Flexible analog input/output mixers
  • Stereo digital microphone inputs
  • PLL supporting input clocks from 8 MHz to 27 MHz
  • Microphone bias reference voltage
  • Analog and digital I/O: 1.8 V to 3.65 V
  • I2C and SPI control interfaces
  • Digital audio serial data I/O: stereo (I2S) and time-division multiplexing (TDM) modes
  • 32-lead, 5 mm × 5 mm LFCSP
  • -40◦C to +85◦C operating temperature range

For more detailed information please refer to the ADAU1761 datasheet.

Board parameters

Supply Voltages

  • 3.3V from Beaglebone headers P8 and P9

Internal Voltages from 3.3V supply

  • 3.3V for configuration EEPROM
  • 3.0V for audio codecs
  • 1.0V for hearing aid dummies or microphone bias

Board components

  • Audio (ADAU1761)
  • Audio bus merger: 3-input logic OR-Gate (SN74LVC1G332DBVR)
  • Power Management: Voltage Regulation (MAX8902A, MAX8902B)
  • Memory: Beaglebone configuration EEPROM (CAT24C256)

Specification and Technical Reference Manual

Hardware Design Files and Kernel Driver Files

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Publications / Conference Contributions

  • Linux Audio Conference 2017
    Open Signal Processing Software Platform for Hearing Aid Research (openMHA) (paper, video)

  • Journal of the Acoustical Society of America, Vol 143, No. 3
    Open portable platform for hearing aid research (publication, slides)

  • American Auditory Society, 2018 Annual Meeting
    Hearing4all: Open Portable Platform for Hearing Aid Research (status report)

  • Hearing Aid Developers Forum
    NIH (NIDCD) initiative to develop real-time portable signal processing tools for advancing research on hearing loss compensation (slides)

  • Linux Audio Conference 2018
    Open Hardware Multichannel Sound Interface for Hearing Aid Research on BeagleBone Black with openMHA: Cape4all (paper, event, video)

  • Embedded Linux Conference 2018
    PREEMPT_RT isn’t Just for Lasers: The Perfect Match for Hearing Aid Research! (slides, event, video)

News articles

Project partners

  • Carl von Ossietzky University of Oldenburg
    Department of Medical Physics and Acoustics
  • HörTech gGmbH, Oldenburg
  • Leibniz University of Hannover
    Institute of Microelectronic Systems
  • Cluster of Excellence “Hearing4all”
  • 64 Studio Ltd, Isle of Wight, UK
  • Bat&Cat SoundLabs, Palo Alto, USA
  • Advanced Sensor Integrations

Partner links

The openMHA platform

openMHA is both an open community platform for hearing aid algorithm research and an open-source software platform for real-time audio signal processing, licensed under AGPL-3.0.

openMHA on Raspberry Pi


At the Carl von Ossietzky University in Oldenburg we developed a mobile hearing aid prototype with a Raspberry Pi 3. Therefore, we used mainly consumer hardware with a combined value of about 250€ and only open source software. It is based on the open Master Hearing Aid (open source hearing aid software) and we will use it for teaching and research. We provide instructions to build the prototype as well as an SD card image which comes with a fully functional pre-configured setup.

Main characteristics

  • Efficient real-time implementations of research-approved hearing algorithms
  • Looks like wearing in-ear headphones
  • Competitively low delays
  • Whole setup fits in a belt bag

Some cool features

  • Pre-configured SD-card image
  • Several hours of autonomy
  • Connect via wifi to the hearing aid prototype
  • Fit it to a specific hearing profile using openMHA’s graphical fitting interface
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Hört sich für unsere Anforderungen gut an!

Noch eine heise-Meldung dazu:

Das cape4all wird in einer modifizierten Version auch beim Citizen-Science-Projekt (gleiche Förderreihe wie bei BOB??) Hearable / liketohear des Fraunhofer IDMT eingesetzt!

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