BiquadFilterNode
================

The `BiquadFilterNode` interface represents a simple low-order filter, and is created using the `BaseAudioContext/createBiquadFilter` method. It is an `AudioNode` that can represent different kinds of filters, tone control devices, and graphic equalizers. A `BiquadFilterNode` always has exactly one input and one output.

EventTarget

AudioNode

BiquadFilterNode

|  |  |
| --- | --- |
| Number of inputs | `1` |
| Number of outputs | `1` |
| Channel count mode | `"max"` |
| Channel count | `2` (not used in the default count mode) |
| Channel interpretation | `"speakers"` |

Constructor
-----------

`BiquadFilterNode()`

Creates a new instance of a `BiquadFilterNode` object.

Instance properties
-------------------

*Inherits properties from its parent, `AudioNode`*.

**Note:** Though the `AudioParam` objects returned are read-only, the values they represent are not.

`BiquadFilterNode.frequency` Read only 

An a-rate `AudioParam`, a double representing a frequency in the current filtering algorithm measured in hertz (Hz).

`BiquadFilterNode.detune` Read only 

An a-rate `AudioParam` representing detuning of the frequency in cents.

`BiquadFilterNode.Q` Read only 

An a-rate `AudioParam`, a double representing a Q factor, or *quality factor*.

`BiquadFilterNode.gain` Read only 

An a-rate `AudioParam`, a double representing the gain used in the current filtering algorithm.

`BiquadFilterNode.type`

A string value defining the kind of filtering algorithm the node is implementing.


 The meaning of the different parameters depending on the type of the filter
 (detune has the same meaning regardless, so isn't listed below)
 | `type` | Description | `frequency` | `Q` | `gain` |
| --- | --- | --- | --- | --- |
| `lowpass` | 
 Standard second-order resonant lowpass filter with 12dB/octave rolloff.
 Frequencies below the cutoff pass through; frequencies above it are
 attenuated.
  | The cutoff frequency. | 
 Indicates how peaked the frequency is around the cutoff. The greater the
 value is, the greater is the peak.
  | *Not used* |
| `highpass` | 
 Standard second-order resonant highpass filter with 12dB/octave rolloff.
 Frequencies below the cutoff are attenuated; frequencies above it pass
 through.
  | The cutoff frequency. | 
 Indicates how peaked the frequency is around the cutoff. The greater the
 value, the greater the peak.
  | *Not used* |
| `bandpass` | 
 Standard second-order bandpass filter. Frequencies outside the given
 range of frequencies are attenuated; the frequencies inside it pass
 through.
  | The center of the range of frequencies. | 
 Controls the width of the frequency band. The greater the
 `Q` value, the smaller the frequency band.
  | *Not used* |
| `lowshelf` | 
 Standard second-order lowshelf filter. Frequencies lower than the
 frequency get a boost, or an attenuation; frequencies over it are
 unchanged.
  | The upper limit of the frequencies getting a boost or an attenuation. | *Not used* | The boost, in dB, to be applied; if negative, it will be an attenuation. |
| `highshelf` | 
 Standard second-order highshelf filter. Frequencies higher than the
 frequency get a boost or an attenuation; frequencies lower than it are
 unchanged.
  | The lower limit of the frequencies getting a boost or an attenuation. | *Not used* | The boost, in dB, to be applied; if negative, it will be an attenuation. |
| `peaking` | 
 Frequencies inside the range get a boost or an attenuation; frequencies
 outside it are unchanged.
  | The middle of the frequency range getting a boost or an attenuation. | 
 Controls the width of the frequency band. The greater the
 `Q` value, the smaller the frequency band.
  | The boost, in dB, to be applied; if negative, it will be an attenuation. |
| `notch` | 
 Standard
 notch
 filter, also called a *band-stop* or
 *band-rejection* filter. It is the opposite of a bandpass filter:
 frequencies outside the give range of frequencies pass through;
 frequencies inside it are attenuated.
  | The center of the range of frequencies. | 
 Controls the width of the frequency band. The greater the
 `Q` value, the smaller the frequency band.
  | *Not used* |
| `allpass` | 
 Standard second-order
 allpass
 filter. It lets all frequencies through, but changes the
 phase-relationship between the various frequencies.
  | 
 The frequency with the maximal
 group delay, that is, the frequency where the center of the phase transition
 occurs.
  | 
 Controls how sharp the transition is at the medium frequency. The larger
 this parameter is, the sharper and larger the transition will be.
  | *Not used* |

Instance methods
----------------

*Inherits methods from its parent, `AudioNode`*.

`BiquadFilterNode.getFrequencyResponse()`

From the current filter parameter settings this method calculates the frequency response for frequencies specified in the provided array of frequencies.

Example
-------

See `AudioContext.createBiquadFilter` for example code that shows how to use an `AudioContext` to create a Biquad filter node.

Specifications
--------------

| Specification |
| --- |
| Web Audio API # BiquadFilterNode |

Browser compatibility
---------------------

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See also
--------

* Using the Web Audio API