[music-dsp] RIAA inverse curve

[Frederick Umminger]

RIAA equalization can be done very well with a single biquad, the
coefficients of
which can be found in the music-dsp source code archive. I posted these in
October.

I forget whether the was the RIAA curve or the inverse but since they are
related by swapping numerator and denominator in the transfer function, you
can easily get both from the posted coefficients.

These were not computed from the bilinear transform and they suffer no
warping.

If you are concerned about precision problems at low frequencies, the
solution is to use alternative filter structures for implementing biquads.
Zolzer's book has a nice overview of some of these.

-Frederick Umminger


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