Author: Scott Gravenhorst
Verilog, designed for Spartan-3A DSP 1800 FPGA (dev. board).
Harp Physical Model
Description: This MIDI synthesizer uses Karplus-Strong string models to create a harp of 56 strings. It is 56 voice polyphonic and outputs in stereo with the bass strings more to the left channel and the treble strings more to the right. Each string has it's own position in the stereo field. A delay of 1.28 mS is also applied to the right channel (the delay is part of the synth logic). Each string is modeled in only one dimension to allow for the largest number of strings in the available FPGA RAM.
Timbre control is accomplished by setting values for the reflection filters and attenuator using MIDI continuous controllers (in my case, a Wavestation's joystick and the modulation wheel). These parameters allow for very long metallic sustain down to a rather plinky sound. At this point in time, there is no "wood" in the synth, i.e., there is no physical model of a wooden harp frame, yet the instrument can still sound very harp like and very natural.
Internally, the synth is composed of 8 "mini-harps" of 7 strings each. The mini-harps are all executed in parallel to allow a high sample rate (198 KHz).