svfilter.dsp

State-variable filter.

Function

This instrument is a state-variable filter.

To convert a frequency in Hz to the value needed to set the filter, the following formula, from Hal Chamberlain's "Musical Applications of MicroProcessors," is used:

F1 = 2sin(PI*Frequency/SampleRate)

where

F1 is the frequency control parameter for the filter.
Frequency is Frequency in Hertz
SampleRate is 44100.0

If Frequency/SampleRate is small, for example less than 1/5, you can use an approximation, as follows:

F1 = 2*PI*Frequency/SampleRate

To calculate a fixed point value suitable for TweakRawKnob( ItemNumber, FKnob), if F1 is expressed as a 16.16 fixed point value (frac16), then:

FKnob = F1>>1;

because FKnob is a 1.15 fixed point value.

Knobs

Frequency- currently nonlinear

Resonance - 1 / Q, 0 => $7FFF

Amplitude- 0 => $7FFF

Inputs

Input - signal

Outputs

Output

Input FIFOs

None

Output FIFOs

None

Resources

Ticks = 19

N memory = 19 words