BiquadFilterNode: Q property

The Q property of the BiquadFilterNode interface is an a-rate AudioParam, a double representing a Q factor, or quality factor.

Value

An AudioParam. Its defaultValue is 1, and its minValue and maxValue are ±(2¹²⁸ - 2¹⁰⁴), or approximately ±3.403e38. This is the range of single-precision floating-point numbers.

Its actual value range depends on the filter's type:

• For lowpass and highpass, the Q value is interpreted to be in dB. For these filters the value range is [-Q, Q] where Q is the largest value for which 10^Q/20 does not overflow the bound above. This is approximately 770.63678.
• For bandpass, notch, allpass, and peaking, the Q value is related to the bandwidth of the filter and should be positive, but there's no stricter maximum than the above.
• It is not used for lowshelf and highshelf filters.

Examples

The following example shows basic usage of an AudioContext to create a Biquad filter node. For more complete applied examples/information, check out our Voice-change-O-matic demo (see app.js lines 108–193 for relevant code).

const audioCtx = new AudioContext();

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

biquadFilter.type = "peaking";
biquadFilter.frequency.value = 1000;
biquadFilter.Q.value = 100;
biquadFilter.gain.value = 25;

Specifications

Browser compatibility

See also

• Using the Web Audio API