Biquad Filter

Second-order IIR (biquad) filter supporting seven filter types. Based on the Audio EQ Cookbook by Robert Bristow-Johnson.

Transfer function:

\[H(z) = \frac{b_0 + b_1 z^{-1} + b_2 z^{-2}}{a_0 + a_1 z^{-1} + a_2 z^{-2}}\]

Only five multiplications and four additions per sample, making it efficient for real-time audio.

Filter types

Constant	Type	Description
LPF	Low-pass	Passes frequencies below the cutoff
HPF	High-pass	Passes frequencies above the cutoff
BPF	Band-pass	Passes frequencies near the centre frequency
NOTCH	Notch	Rejects frequencies near the centre frequency
PEQ	Peaking EQ	Boost or cut at the centre frequency
LSH	Low shelf	Boost or cut all frequencies below the cutoff
HSH	High shelf	Boost or cut all frequencies above the cutoff

class pyminidsp.BiquadFilter(filter_type, freq, sample_rate, db_gain=0.0, bandwidth=1.0)

Biquad (second-order IIR) filter.

Supports low-pass, high-pass, band-pass, notch, peaking EQ, low shelf, and high shelf filter types.

Example

>>> filt = BiquadFilter(LPF, freq=1000.0, sample_rate=44100.0)
>>> for sample in signal:
...     output = filt.process(sample)

# Low-pass at 1 kHz, process a full signal
lpf = md.BiquadFilter(md.LPF, freq=1000.0, sample_rate=44100.0)
filtered = lpf.process_array(signal)

# Peaking EQ: +6 dB at 3 kHz
eq = md.BiquadFilter(md.PEQ, freq=3000.0, sample_rate=44100.0, db_gain=6.0)

# Sample-by-sample processing
for sample in signal:
    out = lpf.process(sample)

process(sample)

Process a single sample through the filter.

process_array(signal)

Process an entire signal through the filter.

Parameters:

signal – Input numpy array.

Returns:

Filtered numpy array.