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• Measure feedback and Input-Output functions

  Marc René Schädler • 12/30/2017 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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