Asterisk DSP

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I don't have time for this work.


This project will focus on improvement of the goertzel algorithm in asterisk's dsp.c. This won't be an improvement to the algorithms themselves, but more to the frequencies detectable by the code. It is currently detects US tones only which limits call progress severely. The ultimate goal of this project is to get the code submitted and into trunk so that it can go into the next major release of Asterisk.

Frequencies already supported:

  • US Modes
    • 350Hz
    • 440Hz
    • 480Hz
    • 620Hz
    • 950Hz
    • 1400Hz
    • 1800Hz
  • CR/BR Modes
    • 425Hz
  • UK Modes
    • 400Hz

Additional frequencies required for near-total international support:

  • Used by some countries
    • 450Hz
  • Used only by Japan
    • 384Hz
    • 416Hz
  • Used only by the Netherlands
    • 150Hz
  • Used only by Singapore
    • 270Hz
    • 320Hz


This project stemmed from the time I spent in tech support at Digium. Foreign customers always complained that call progress detection was either unavailable for them, or buggy.

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