# biquad~

## 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 message, or by turning the audio on and off).

## Examples

## Arguments

### a0 [float]

Set the initial value for the a0 filter coefficient. If a signal is connected to the second inlet, the coefficient supplied as an argument is ignored.

### a1 [float]

Set the initial value for the a1 filter coefficient. If a signal is connected to the third inlet, the coefficient supplied as an argument is ignored.

### a2 [float]

Set the initial value for the a2 filter coefficient. If a signal is connected to the fourth inlet, the coefficient supplied as an argument is ignored.

### b1 [float]

Set the initial value for the b1 filter coefficient. If a signal is connected to the fifth inlet, the coefficient supplied as an argument is ignored.

### b2 [float]

Set the initial value for the b2 filter coefficient. If a signal is connected to the sixth inlet, the coefficient supplied as an argument is ignored.

## Attributes

### smooth [int] (default: 1)

Toggles the smoothing of filter coeffient changes.

### Common Box Attributes

## Messages

### int

#### Arguments

The coefficients in inlets 2 to 6 may be specified by a number instead of a signal. If a signal is also connected to the inlet, the number value is ignored.

### float

#### Arguments

### list

#### Arguments

a1 [float]

a2 [float]

b1 [float]

b2 [float]

### clear

### dictionary

#### Arguments

### signal

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

#### Arguments

a1 [float]

a2 [float]

b1 [float]

b2 [float]

## Output

### signal

The filtered signal.

## See Also

Name | Description |
---|---|

Sound Processing Techniques | Sound Processing Techniques |

buffir~ | |

cascade~ | |

comb~ | |

cross~ | |

filtergraph~ | |

lores~ | |

onepole~ | |

reson~ | |

svf~ | |

teeth~ | |

Audio Filtering | Audio Filtering |