BUTTERHP

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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 opcode can also be written butlp, buthp, butbp, butbr.

PERFORMANCE

These new 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 - Cuttoff or center frequency for each of the filters.

kband - Bandwidth of the bandpass and bandreject filters.

iskip - Skip initialisation 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

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