BiquadFilterNode

BiquadFilterNode() 构造函数创建一个新的BiquadFilterNode对象, 这个对象通过AudioContext.createBiquadFilter()方法创建，表示一个简单的低阶滤波器.

语法

var biquadFilterNode = new BiquadFilterNode(context, options)

参数

context

AudioContext 的一个引用.

options可选

可选配置项如下:

• type: 值为其中之一"lowpass", "highpass", "bandpass", "lowshelf", "highshelf", "peaking", "notch", "allpass". 其他选项的含义取决于此选项的值.

低通滤波器: 允许低于截止频率的频率通过, and attenuates frequencies above the cutoff. This is a standard second-order resonant lowpass filter with 12dB/octave rolloff.

• Q: Controls how peaked the response will be at the cutoff frequency. A large value makes the response more peaked. Please note that for this filter type, this value is not a traditional Q, but is a resonance value in decibels.
• frequency: The cutoff frequency.
• gain: Not used.

highpass: A highpass filter is the opposite of a lowpass filter. Frequencies above the cutoff frequency are passed through, but frequencies below the cutoff are attenuated. It implements a standard second-order resonant highpass filter with 12dB/octave rolloff.

• Q: Controls how peaked the response will be at the cutoff frequency. A large value makes the response more peaked. Please note that for this filter type, this value is not a traditional Q, but is a resonance value in decibels.
• frequency: The cutoff frequency.
• gain: Not used.

bandpass: A bandpass filter allows a range of frequencies to pass through and attenuates the frequencies below and above this frequency range. It implements a second-order bandpass filter.

• Q: Controls the width of the band. The width becomes narrower as the Q value increases.
• frequency: The center of the frequency band.
• gain: Not used.

lowshelf: The lowshelf filter allows all frequencies through, but adds a boost (or attenuation) to the lower frequencies. It implements a second-order lowshelf filter.

• Q: Not used.
• frequency: The upper limit of the frequences where the boost, or attenuation, is applied.
• gain: The boost, in dB, to be applied. If the value is negative, the frequencies are attenuated.

highshelf: The highshelf filter is the opposite of the lowshelf filter and allows all frequencies through, but adds a boost to the higher frequencies. It implements a second-order highshelf filter.

• Q: Not used.
• frequency: The lower limit of the frequences where the boost, or attenuation, is applied.
• gain: The boost, in dB, to be applied. If the value is negative, the frequencies are attenuated.

peaking: The peaking filter allows all frequencies through, adding a boost, or attenuation, to a range of frequencies.

• Q: The width of the band of frequencies that are boosted. A large value implies a narrow width.
• frequency: The center frequency of the boost range.
• gain: The boost, in dB, to be applied. If the value is negative, the frequencies are attenuated.

notch: The notch filter (also known as a band-stop, or band-rejection filter) is the opposite of a bandpass filter. It allows all frequencies through, except for a set of frequencies.

• Q: The width of the band of frequencies that are attenuated. A large value implies a narrow width.
• frequency: The center frequency of the attenuation range.
• gain: Not used.

allpass: An allpass filter allows all frequencies through, but changes the phase relationship between the various frequencies. It implements a second-order allpass filter.

• Q: The sharpness of the phase transition at the center frequency. A larger value implies a sharper transition and a larger group delay.
• frequency: The frequency where the center of the phase transition occurs. Viewed another way, this is the frequency with maximal group delay.
• gain: Not used.

Specifications

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