[sdiy] Formant filters, yay!

Elain Klopke functionofform at gmail.com
Thu Mar 9 19:50:11 CET 2017

> I'm a bit suspicious of those tabulated formant values...  The f3, f4 and
> f5 formants are all very close together, and those combinations of centre
> frequency vs bandwidth result in some pretty high Q values!  Maybe they are
> right but something seems a bit fishy about them to me.
Hmm... I don't know much about the frquencies, but maybe the bandwidth is
from one end of the band to the other end, where the calculations in the
filter book I'm working with assumes bandwidth is from the center frequency
to one end, possibly cutting the bandwidth in half will work. Yay

> 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...

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