biquad~

Two-pole, two-zero filter

Description

biquad~ implements a two-pole, two-zero filter using the following equation:

y[n] = a0 * x[n] + a1 * x[n-1] + a2 * x[n-2] - b1 * y[n-1] - b2 * y[n-2]

You can specify the coefficients a0, a1, a2, b1, and b2 as signals or floats (if you make the filter explode by making the b coefficients too high, you can recover (after lowering them) with the clear message, or by turning the audio on and off). .

Arguments

Name Type Opt Description
filter-parameters (5 floats) list opt Up to five numbers, to set initial values for the coefficients a0, a1, a2, b1, and b2. If a signal is connected to a given inlet, the coefficient supplied as an argument for that inlet is ignored.

Messages

int filter-coefficient [int]
Converted to float.
float filter-coefficient [float]
The coefficients in inlets 2 to 6 may be specified by a float instead of a signal. If a signal is also connected to the inlet, the float is ignored.
list filter-coefficients (5 floats) [list]
The five coefficients can be provided as a list in the left inlet. The first number in the list is coefficient a0, the next is a1, and so on. If a signal is connected to a given inlet, the coefficient supplied in the list for that inlet is ignored.
clear Clears the biquad~ object's memory of previous inputs and outputs, resetting xn-1, xn-2, yn-1, and yn-2 to 0.
signal In left inlet: Signal to be filtered. The filter mixes the current input sample with the two previous input samples and the two previous output samples according to the formula:

yn = a0xn + a1xn-1 + a2xn-2 - b1yn-1 - b2yn-2.

In 2nd inlet: Amplitude coefficient a0, for scaling the amount of the current input to be passed directly to the output.

In 3rd inlet: Amplitude coefficient a1, for scaling the amount of the previous input sample to be added to the output.

In 4th inlet: Amplitude coefficient a2, for scaling the amount of input sample n-2 to be added to the output.

In 5th inlet: Amplitude coefficient b1, for scaling the amount of the previous output sample to be added to the current output.

In right inlet: Amplitude coefficient b2, for scaling the amount of output sample n-2 to be added to the current output. .
stoke filter coefficient values [list]
The word stoke, followed by a list that specifies a set of filter coefficient values, will preload the filter so that it starts in a given initial state, allowing the filter to be used for purposes such as a ringing oscillator.

Attributes

Name Type g/s Description
smooth int
def.:1
Toggles the smoothing of filter coeffient changes. .

Information for box attributes common to all objects

Output

signal: The filtered signal.

Examples

Filter coefficients may be supplied as numerical values or as varying signals

See Also

Name Description
buffir~ buffer-based FIR filter
cascade~ Cascaded series of biquad filters
comb~ Comb filter
filtergraph~ Graphical filter editor
lores~ Resonant lowpass filter
onepole~ Single-pole lowpass filter
reson~ Resonant bandpass filter
teeth~ Comb filter with feedforward and feedback delay control