BiquadFilterNode - Web APIs 编辑

The BiquadFilterNode interface represents a simple low-order filter, and is created using the AudioContext.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.

Constructor

BiquadFilterNode()

Creates a new instance of a BiquadFilterNode object.

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

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

BiquadFilterNode.detune Read only

Is an a-rate AudioParam representing detuning of the frequency in cents.

BiquadFilterNode.Q Read only

Is an a-rate AudioParam, a double representing a Q factor, or quality factor.

BiquadFilterNode.gain Read only

Is an a-rate AudioParam, a double representing the gain used in the current filtering algorithm.

BiquadFilterNode.type

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

The meaning of the different parameters depending of 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

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

The following example shows basic usage of an AudioContext to create a Biquad filter node. For a complete working example, check out our voice-change-o-matic demo (look at the source code too).

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();

//set up the different audio nodes we will use for the app
var analyser = audioCtx.createAnalyser();
var distortion = audioCtx.createWaveShaper();
var gainNode = audioCtx.createGain();
var biquadFilter = audioCtx.createBiquadFilter();
var convolver = audioCtx.createConvolver();

// connect the nodes together

source = audioCtx.createMediaStreamSource(stream);
source.connect(analyser);
analyser.connect(distortion);
distortion.connect(biquadFilter);
biquadFilter.connect(convolver);
convolver.connect(gainNode);
gainNode.connect(audioCtx.destination);

// Manipulate the Biquad filter

biquadFilter.type = "lowshelf";
biquadFilter.frequency.setValueAtTime(1000, audioCtx.currentTime);
biquadFilter.gain.setValueAtTime(25, audioCtx.currentTime);

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Using the Web Audio API