Ensoniq DP4 Audio Effects Processor
There were four ESP DSP chips* designed into this unit, which means four distinct channels of processing. Each processor was a parallel processor capable of about 300 VLIW instructions per sample period. That necessitated highly efficient real-time programming. The original CPU design was by Bill Mauchly and Steve Hoge. Mauchly, I, and Dave Andreas later redesigned the ESP from scratch for which we received a patent. Mike Arnao wrote a beautiful symbolic assembler; he made programming the unit a real joy. The programming language we developed for the unit is a model of elegance and power.
*(Thanks to Matthew Craig and Charles Duffy of Paris Users Group for preserving all the ESP and ESP2 documentation, source code, and assembler. ESP2 chip fabrication data was preserved by David Andreas of Silicon Labs and Alan K. Smith of Aviom Inc.)
Joe Bryan wrote the original Leslie rotating speaker simulator by physical modeling. The effect is striking, especially on headphones. I later developed the distortion algorithms for it to get that Hammond B3 sound. Except for the Delays and the Vocal Remover, I designed all the algorithms for this unit, listed below:
The strength of this unit were its reverberators, vocoder design (used to make talk nearly anything that makes sound; e.g. talking wind or waterfall), speaker emulation, nonlinear (chaotic) distortion for harmonic enhancement (a van der Pol oscillator), and crystal clear choruses employing allpass interpolation: http://ccrma.stanford.edu/~dattorro/EffectDesignPart2.pdf
Tom Metcalf and John Senior and I spent an enormous amount of time developing the algorithms for guitar distortion. It remains utterly astounding how discerning rock guitarists are regarding distortion. It is reminiscent of violinists' discernment of tone quality in very old wooden instruments. Hence the time we spent. About 15,000 of these units were shipped since its introduction in 1992.