bqrez — A second-order multi-mode filter.


A second-order multi-mode filter.


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


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)


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.


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

Example 110. Example of the bqrez opcode borrowed from the rezzy opcode in Kevin Conder's manual.

See the sections Real-time Audio and Command Line Flags for more information on using command line flags.

; 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

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


;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



See also

Standard Filters: Resonant Low-pass filters


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