4 String Karplus-Strong Bass


The 4 String Karplus-Strong synth is just that. A MIDI controlled synth that implements 4 Karplus-Strong strings. The instrument's timbre is controlled by 2 pots, one for the reflection filter (which determines how quickly harmonics are rolled off) and a damping factor which causes the waveform to decay linearly across the spectrum. No pitch bend is implemented. Mod wheel controls the width of the excitation pulse.

The synth with included MIDI controller is contained in one dsPIC IC.

Voice assignment consists of logic using a "gates" memory which is used to determine which voices are available. Part of the algorithm for deciding which voice is selected includes scanning the string models for any that are already set to the pitch of a newly received note on message. This feature provides two things:
1: A more realistic sound in that when the same pitch is played more than once on a real harp, the same string is reused. The synth does this whenever possible which results in fewer voices being stolen from another pitch. When a vibrating string is replucked, there is already wave information in the delay line. The pluck pulse modifies some of this data, so the new pluck can sound different just as it does with a real harp (or other struck or plucked string instrument).
2: Voice theft for new notes is limited and occurs when no matching pitch string can be found and when all voices are already in use. Unused voices are always used before sounding voices are stolen. The code is written in assembly language.

Musical Examples of the 4 String Karplus-Stromg Bass Instrument

  • No Demo is available at this time.