Portfolio Noah Vawter. 21xx Effect Algorithm Demos

## Original Signal Processing Algorithms

This page reveals audible demos of the effect prozessor programs I've developed. Since I do not like to recreate the wheel, you will find no "distortion, reverb, phaser," etc. programs in here. I respect them, yet decline becoming the 85,000th person to write them. I spend my time exploring things no one else has thought of.

All demos were created live. The signal sources were an FR-777 303-clone and an SPS-1 drum machine. The effect algorithms all ran in realtime on an EZ-Kit Lite equipped with an Analog Devices 2181 DSP and 1847 codec. To control the effects, I used "Burrito" running on a palm pilot to send MIDI controller messages to the 2181.

To make clear comparisons, in all examples the dry version of the sound is in the left channel while the wet is in the right.

• Effect #1 - Domain I named this effect domain because the program renders the input stream into the modulation domain. Once that conversion has taken place, the user manipulates parameters to munge up the sound before reverse-transformation.

The modulation domain resembles the frequency and time domain, except in this domain, artifacts and distortions from the modulation stream develop into exotic timbre shifts. Melodies can acquire spontaneous portamento effects. The rules of superposition no longer apply.

• Effect #2 - Harmonic Equalizer This algorithm is used to create subtle timbre shifts. It functions like an equalizer, however, the great difference between this program and a frequency equalizer is that the 8 sliders correspond to *harmonics* of the input signal (as opposed to fixed frequency bands). For example, the sliders can mix levels of overtones of the input signal to transform a sine wave into a square wave. The same slider settings would turn a triangle wave into....(who knows!)

The effect of the sliders can be viewed as a bank of parallel, ascending pitch-scalers. However, Harm E.Q. is not just limited to overtones of the form 1x, 2x, 3x, etc. The starting pitch, the delta from slider to slider, and finally the denominator in the pitch-scale ratio can all be modified in realtime. This means many rational combinations of overtones can be synthesis, e.g. 5/3, 6/3, 7/3, ... 12/3, or 3/5, 6/5, 9/5, 12/5, ... 24/5. Just for the fun of sonic variety, there is a feedback adjustment which you can tweak to the point of overdrive.

• Effect#3 - F. Madness "Frequency Modulation Madness." The algorithm is so simple: Audio input is scaled and summed to an accumulator which serves as the phase for a sinusoidal waveform lookup. How does it change so much? Several other sliders, including portamento, and sample and hold period breakdown the one-to-one ratio of input sample to output frequency. Furthermore, a variable bit mask on the phase delta offers a feature which can not be easily obtained with a purely analog frequency modulator- it quantizes the output signal into a limited number of frequencies.

• Effect #4 - Skank With its array of hastily-implemented effects, Skank is a lo-fi parody of a guitar multi-effects processor. To be tweaked: pitch-scale, distortion, delay w/ feedback and ring-modulation. Unique features include Pulse Width Modulation (for reedy tone and variable duty cycle tremolo), portamento-pitch-scale and a hold buffer with reverse playback capability.

You can find more demonstration audio of this algorithm is available online.

## Summary

After hearing those demos, I hope your auditory appreciation system has been thrown curveballs- not merely paths from mound to plate difficult to spot, but ones which languish before your imagination in the form of beautiful curves, composed from a multitude of ever-varying waveforms, recombining before your senses for the first time in configurations you may once have dreamed of, yet only rarely had the chance to experience and modify in real-time...until now.