[Audacity-nyquist] Nyquist A-weighting filter: reverse-engineer solution

[<edg...@we...>]

Nyquist A-weighting filter: reverse-engineer solution

Because I also like to 'abuse' Nyquist and Audacity for audio
measurement purposes I have sat down and reverse-engineered a
Nyquist A-weighting filter.

I have to say that the code is real dumb, but I have tried for
several hours to replace the lots of nested lp's and hp's with
higer order filters ending up with much worse results.

I assume that because a-weighting is 'stone-age' technology
(it was invented somewhere in the 1960s) it probably works
best with 'stone-age' designed code.

The original audio measurement instrument can be found on:

http://www.beis.de/Elektronik/AudioMeasure/WeightingFilters.html

To test the filter I have generated a 'white noise' track at -12dB
in Audacity, applied the filter with 'Effects - Nyquist Prompt' and
the resulting noise curve was nearly exact the same as this one:

http://www.diracdelta.co.uk/science/source/a/w/aweighting/source.html

Finally the nyquist code:

(scale (db-to-linear 3)
(lp (lp (hp (hp (hp (hp s 20.6) 20.6) 107.7) 737.9) 12200) 12200))




regards,

- edgar




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