MIDI Controlled Sample-Based Synthesizer

Amir Hirsch and Andrew Leiserson

Sampling  |  MIDI  |  Interpolation  |  Filtering

A filter alters the spectrum of a signal. For musical applications, a filter is used to change the timbre of the sound being played. The output of a finite impulse response (FIR) filter is computed as the weighted sum of the current and previous inputs. An infinite impulse response (IIR) filter uses feedback, and thus uses previous outputs in addition to inputs to compute the filtered output. FIR filters are easier to design, but require more computation per output sample. In contrast, IIR filters are notoriously difficult to design and can be unstable if designed incorrectly.

The filter used for our sampler was an IIR filter, based on the "Moog VCF variation 1" on MusicDSP.org. For an audio demo of the filter click here . In addition to the MusicDSP site, for a good introduction to digital signal processing and filtering visit the Bores "Introduction to DSP."