bqrez

A second-order multi-mode filter.

Syntax

ares bqrez asig, xfco, xres [, imode] [, iskip]

Initialization

imode (optional, default=0) -- The mode of the filter. Choose from one of the following:

• 0 = low-pass (default)
• 1 = high-pass
• 2 = band-pass
• 3 = band-reject
• 4 = all-pass

iskip (optional, default=0) -- if non zero skip the initialisation of the filter. (New in Csound version 4.23f13 and 5.0)

Performance

ares -- output audio signal.

asig -- input audio signal.

xfco -- filter cut-off frequency in Hz. May be i-time, k-rate, a-rate.

xres -- amount of resonance. Values of 1 to 100 are typical. Resonance should be one or greater. A value of 100 gives a 20dB gain at the cutoff frequency. May be i-time, k-rate, a-rate.

All filter modes can be frequency modulated as well as the resonance can also be frequency modulated.

bqrez is a resonant low-pass filter created using the Laplace s-domain equations for low-pass, high-pass, and band-pass filters normalized to a frequency. The bi-linear transform was used which contains a frequency transform constant from s-domain to z-domain to exactly match the frequencies together. Alot of trigonometric identities where used to simplify the calculation. It is very stable across the working frequency range up to the Nyquist frequency.

Examples

Here is an example of the bqrez opcode. It uses the file bqrez.csd.

<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
-odac     ;;;RT audio out
;-iadc    ;;;uncomment -iadc if RT audio input is needed too
; For Non-realtime ouput leave only the line below:
; -o bqrez.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

sr = 44100
ksmps = 32
nchnls = 2
0dbfs = 1

instr 1                 ;sawtooth waveform.

kfco  line 200, p3, 2000;filter-cutoff frequency from .2 to 5 KHz.
kres  = p4              ;resonance
imode = p5              ;mode
asig    vco 0.2, 220, 1
afilt   bqrez asig, kfco, kres, imode
asig    balance afilt, asig
        outs asig, asig

endin

</CsInstruments>
<CsScore>
;sine wave
f 1 0 16384 10 1

i 1 0 3 1 0             ; low pass
i 1 + 3 30 0            ; low pass
i 1 + 3 1 1             ; high pass
i 1 + 3 30 1            ; high pass

e

</CsScore>
</CsoundSynthesizer>

See also

Standard Filters: Resonant Low-pass filters

Credits

Author: Matt Gerassimoff
New in version 4.32
Written in November 2002.