butterhp, butterlp, butterbp, butterbr

  ar      butterhp   asig, kfreq[, iskip]
  ar      butterlp   asig, kfreq[, iskip]
  ar      butterbp   asig, kfreq, kband[, iskip]
  ar      butterbr   asig, kfreq, kband[, iskip]

Description

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.

Performance

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.

kband - Bandwidth of the bandpass and bandreject filters.

iskip - Skip initialization if present and non zero

Example

  asig    rand      10000           ; White noise signal
  alpf    butterlp  asig, 1000      ; cutting frequencies above1K
  ahpf    butterhp  asig, 500       ; passing frequencies above 500Hz
  abpf    butterbp  asig, 2000, 100 ; passing only 1950 to 2050 Hz
  abrf    butterbr  asig, 4500, 200 ; cutting only 4400 to 4600 Hz

Author

Paris Smaragdis
MIT, Cambridge
1995