ar butterhp asig, kfreq[, iskip] ar butterlp asig, kfreq[, iskip] ar butterbp asig, kfreq, kband[, iskip] ar butterbr asig, kfreq, kband[, iskip]
Implementations of second-order high-pass, low-pass, band-pass and band-reject Butterworth filters. Note: these opcodes can also be written butlp, buthp, butbp, butbr.
These filters are Butterworth second-order IIR filters. They are slightly slower than the original filters in Csound, but they offer an almost flat passband and very good precision and stopband attenuation.
asig – Input signal to be filtered.
kfreq – Cutoff or center frequency for each of the filters. In the case of butterbp and butterbr, the center kfreq is the intervalic, not mathematical, center.
kband – Bandwidth of the bandpass and bandreject filters.
iskip – Skip initialization if present and non zero
asig rand 10000 ; White noise signal alpf butterlp asig, 1000 ; cutting frequencies above1K ahpf butterhp asig, 500 ; passing frequencies above 500Hz abpf butterbp asig, 1000, 1500 ; passing 2 octaves: 500 to 2000 Hz abrf butterbr asig, 100, 150 ; cutting 2 octaves: 50 to 200 Hz