Synth Building Blocks: Filters

A number of basic filters are included with SBB, all of which are based off of the biquad two-pole two-zero filter architecture: a highpass, lowpass, bandpass, and bandreject. A ladder filter emulation is also included.

Lowpass and Highpass Filters

All of SBB's filters are based on the biquad filter, which is a two-pole two-zero IIR filter that can be configured into a number of different modes. The four modes that SBB supports are lowpass, highpass, bandpass, and bandreject.

SBB's filter abstractions do not need to be supplied individual filter coefficients, only cutoff frequency values and Q (resonance) values.

Here, the lowpass and highpass filters in the RNBO patch are using the same cutoff and Q values. Both are being fed noise from noise~ to show an approximation of their frequency response, which are seen by patching the output of rnbo~ into Max MSP's spectroscope~ UI object.

Bandpass and Bandreject Filters

SBB's two remaining biquad settings are bandpass (sbb.filter.bp) and bandreject (sbb.filter.br). Like the highpass and lowpass filters, these bandpass filters can be used to create harmonic resonance from the input signal at the specified cutoff frequency by increasing the Q value. Using the bandpass filter will emphasize the resonances, while using the bandreject filter will mask them.

Like any SBB abstraction, we can modulate these input values with the output of any other signal. Here's an example similar to the one found in Synth Building Blocks: Generators, where we have an LFO modulating the frequency cutoff of a resonant bandpass filter. The modulation range is between 440Hz - 880Hz.

Lowpass Ladder Filter

SBB also comes with a lowpass ladder filter (sbb.filter.ladder), which is a ladder or 'lattice' implementation of the biquad lowpass. The ladder filter implementation has a unique sound and interesting history, which you can read more about in this article.