Mobile hearing aid prototype

An almost consumer hardware based mobile prototype of a hearing aid with open source software

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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

Check out our project at GitHub for more information, if you are interested.

The details are explained in the GitHub wiki.

  • 1 × Roland CS-10EM Binaural Microphones/Earphones Headphones with binaural microphones
  • 1 × Semi-custom pre-amplifier Provides voltage for electret microphones and amplifies the signal
  • 1 × (stereo) Low-latency sound card for the Raspberry Pi 3
  • 1 × Raspberry Pi 3 model B Powerful system on a chip
  • 1 × SanDisk Ultra 32Gb microSDHC UHS-I

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  • Measure feedback and Input-Output functions

    Marc René Schädler12/30/2017 at 00:15 0 comments

    Today I added a few script to measure and evaluate some basic properties of the setup: Feedback and amplification.

    Feedback can be measured by playing back white noise and recording which part of it is recorded by the microphones.
    The instructions are detailed in the GitHub Wiki

    The impulse responses are shown in the upper panel, the frequency responses in the lower panel.
    You can see that there is substantial feedback and that is far worse on one side (which probably indicates headphone-lottery).

    Amplification in terms of output level vs. input level can be measured similarly, by feeding signals with determined level and frequency (e.g., sine sweeps) into the signal processing block and recording the corresponding output signals.
    The instructions are detailed in the GitHub Wiki

    The measures of input and corresponding output levels are plotted for an example configuration in the upper panel, where the color indicates frequency bands.
    You can see that the left channel is almost linear between input levels from -60dB FS to -20dB FS, while the right one is compressive (decreasing gain with increasing input level) in the same range.
    The data points are grouped into frequency bands and fitted with a polynomial function.
    From these fits, the figures in the lower panel are derived which show the frequency dependent output levels for given input levels, where each pair is indicated by a different color.

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