[sdiy] Formant filters, yay!

rsdio at audiobanshee.com rsdio at audiobanshee.com
Fri Mar 10 10:52:20 CET 2017

On Mar 9, 2017, at 10:50 AM, Elain Klopke <functionofform at gmail.com> wrote:
>> Also, if those "Amp (dB)" values are the amplitudes of the formant peaks in the frequency spectrum, then they may or may not take into account what the excitation waveform was.  If you go about making a filter bank and drive it from a sawtooth oscillator for example, the sawtooth waveform will already have a -6dB/oct rolloff to it's spectrum before you start boosting and cutting areas with the formant filters.  Something to bear in mind.
> I was going to drive it from the square wave outputs from the note divider chips, if that has any effect on things…

The harmonics of a square wave have the same 1/N amplitudes as a ramp wave, with the only difference being that square only has odd harmonics while ramp (sawtooth) has both odd and even.

i.e. 2nd harmonic -6 dB, 3rd harmonic -9 dB, 4th harmonic -12 dB, 5th harmonic -14 dB, 6th harmonic -15.5 dB, 7th harmonic -17 dB, 8th harmonic -18 dB, 9th harmonic -19 dB, 10th harmonic -20 dB, 11th harmonic -21 dB, 12th harmonic -21.5 dB, 13th harmonic -22.3 dB, 14th harmonic -23 dB, 15th harmonic -23.5 dB, 16th harmonic -24 dB, etc.

Brian Willoughby
Sound Consulting

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