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sowbug / groove

A digital audio workstation (DAW) engine.
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Q filter parameter should have linear to logarithmic mapping #17

Open sowbug opened 2 years ago

sowbug commented 1 year ago

I've read RBJ's Audio EQ Cookbook, and unfortunately "the EE kind of definition" means nothing to me. I can see that for the LPF given in that document, a Q of 1/sqrt(2), or 0.707, means no resonance, with the spectrum starting to drop just a bit below the cutoff frequency and continuing to drop at the expected 12dB/octave. A higher Q produces resonance (a peak around the cutoff). But I can't tell other than empirically where a higher Q stops delivering bang for the buck.

sowbug commented 1 year ago

I've done some tuning of this parameter for the 12db LPF. It's still mysterious to me, but for most cases it sounds OK. Removing from current milestone.

sowbug commented 1 year ago

This issue is now a placeholder for getting the linear/log story straight. See Pirkle DSSPC++ p.71 for MMA's simplified formulas for concave/convex transforms (the ones with the 5/12 fraction).

sowbug commented 1 year ago

Pirkle recommends a single user-facing range of 1 to 10 for Q. DSSPC++, page 173.