INSTRUMENT design – simple first-order IIR filter object
Oreson duplicates the functionality of the older CMIX functions reson and rsnset. It builds a simple IIR filter given a desired center frequency and bandwidth, very useful in parallel for building complicated filter response curves (see the IIR instrument for an example of Oreson use).
The general recursive filter equation used by this object is:
y[n] = a*x[n] + b0*y[n-1] - b1*y[n-2]
where y[n], y[n-1] and y[n-2] are the current and two previous outputs of the equation, and x[n] is the current input. a, b0 and b1 are the coefficients to the equation that determine the characteristics of the filter, depending upon the parameters set in the constructor. Presently the Oreson filter object does not allow for dynamic changes to the filter equation.