What does a Biquad filter do?
A biquad filter is a form of infinite-impulse response (IIR) filter where the numerator and denominator are split into a series of second-order sections connected by gain blocks. This type of filter can replace a large FIR filter that uses an impractical amount of hardware resources.
What is Biquad notch filter?
The biquad~ object is a biquadratic filter. In technical terms, that's a second-order IIR filter with two poles and two zeros; in practical terms, it's a versatile filter that can have a wide variety of characteristics—lowpass, hipass, bandpass, notch, shelf, etc.