BiquadFilterNode

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BiquadFilterNode接口是一个简单的双二阶滤波器, 创建于 AudioContext.createBiquadFilter() 方法. 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.

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"

属性

继承属性自父级的 AudioNode.

BiquadFilterNode.frequency
Is an a-rate AudioParam, a double representing a frequency in the current filtering algorithm measured in hertz (Hz).
BiquadFilterNode.detune
Is an a-rate AudioParam representing detuning of the frequency in cents.
BiquadFilterNode.Q
Is an a-rate AudioParam, a double representing a Q factor, or quality factor.
BiquadFilterNode.gain 只读
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 filer. 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 filer. 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

方法

继承方法自父级的 AudioNode.

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

例子

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.value = 1000;
biquadFilter.gain.value = 25;

规范

Specification Status Comment
Web Audio API
BiquadFilterNode
Working Draft  

浏览器兼容性

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 50 25.0 (25.0)  未实现 15.0webkit
22 (unprefixed)
6.0webkit
Feature Android Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support ? 26.0 1.2 ? ? ? 50

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