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