The IIRFilterNode interface of the Web Audio API is a AudioNode processor which implements a general infinite impulse response (IIR) filter; this type of filter can be used to implement tone control devices and graphic equalizers as well. It lets the parameters of the filter response be specified, so that it can be tuned as needed.

Typically, it's best to use the BiquadFilterNode interface to implement higher-order filters. There are several reasons why:

• Biquad filters are typically less sensitive to numeric quirks.
• The filter parameters of biquad filters can be automated.
• All even-ordered IIR filters can be created using BiquadFilterNode.

However, if you need to create an odd-ordered IIR filter, you'll need to use IIRFilterNode. You may also find this interface useful if you don't need automation, or for other reasons.

IIRFilterNodes have a tail-time reference; they continue to output non-silent audio with zero input. As an IIR filter, the non-zero input continues forever, but this can be limited after some finite time in practice, when the output has approached zero closely enough. The actual time that takes depends on the filter coefficients provided.

IIRFilterNode()

Creates a new instance of an IIRFilterNode object.

This interface has no properties of its own; however, it inherits properties from its parent, AudioNode.

Inherits methods from its parent, AudioNode. It also has the following additional methods:

getFrequencyResponse()

Uses the filter's current parameter settings to calculate the response for frequencies specified in the provided array of frequencies.

You can find a simple IIR filter demo live on Codepen. Also see the source code on GitHub. It includes some different coefficient values for different lowpass frequencies — you can change the value of the filterNumber constant to a value between 0 and 3 to check out the different available effects.

Also see our Using IIR filters guide for a full explanation.

• Using the Web Audio API
• AudioNode
• BiquadFilterNode