Digital resonators in the Klatt synthesizer
Klatt (1980) uses a large number of IIR filters of a very simple kind: IIR filters of the form:
(3.3) y[t] = Ax[t] + By[t-1] + Cy[t-2].
This is a specific version of (3.2), with b 0 called A, b1 to bk = 0, a 1 called B, a2 called C, and a3 to a j = 0. Also, he writes nT, meaning sample number n times sample time interval T, instead of t, but that is just a notational difference.
The frequency f and bandwidth w of each filter are determined by the values of the A, B and C coefficients according to the equations:
(3.4) | C = -e-2![]() |
B = 2e-![]() ![]() |
|
A = 1-B-C |
First, a filter of this kind is applied to an impulse source (a sequence of 0's with 1's at regular intervals). This filtering turns the impulse source into a waveform that looks like the glottal wave and sounds like a glottal buzz . Then, more filters of this kind are applied to the glottal wave model in order to selectively enhance (by bandpass filtering) each of the formants in turn (F1 , F2 , F3 , F4 , F5 ).
Next: Exercises
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