Bi-Quad Filter

What is the Bi-Quad Filter

MDN says:

The BiquadFilterNode interface represents a simple low-order filter, and is created using the BaseAudioContext/createBiquadFilter method. It is an AudioNode that can represent different kinds of filters, tone control devices, and graphic equalizers.

This app used the WaveShaperNode to help synthesize the snare drum, but the Biquad Filter could have been used as well.