For the past few years I've been
developing an audio synthesis engine named Nemi.
Sound is produced by non-linear feedback
networks which have been evolved using genetic algorithms, as the
equations these networks represent are too complex to hand
craft.
Even simple voices are astoundingly complex, and it
is nearly impossible to determine what a given network will
produce beforehand. Key state, note, and velocity can all
dramatically alter the character of the sound.
Most
networks create noise, or silence. Only after several generations
of refinement do useable instruments emerge.
The Nemi
sound engine can be driven by MIDI, tcp connections, or data
files. Beowolf clustering works, but still kludgy at this point,
and each machine must launch it's own daemon before
hand.
Realtime audio is achieved by timing execution speed
for each "K" or control cycle, then cutting (if
necessary) the longest, non-sustaining voices. I'm getting
good results with 440 K cycles per second, that winds up producing
a little more than 2 ms of latency, which is good enough for what
I do.
I've included a few clips in mp3 and ogg format to
illustrate.
Evil
Machine.ogg
Illuminati5.mp3
Midi6.mp3
For
info on instrument modellng and waveguides visit Planet
CCRMA.
A neat project I've been
working on is Enscribe
which transforms color photographs into audio watermarks. It's
neat, check it out.
Another interesting field is that of
audio resynthesis. A Fourier Transform converts data (be it audio,
visual, or other type of data) into discrete frequencies. I
ran into interesting problems while trying to create a noise
removal filter...
JPEG image files use a sister of the
Fourier Transform called the Discrete Cosine Transform or DCT or
achieve high compression ratios. If the compression is set too
high, the image starts too resemble a mosaic of blurry
blocks.
The blur and the wavy lines around edges (Gibbs
Phenomena), are caused by a loss of low amplitude spectra. A
similar effect can be done with audio, creating a smeared sound
image. If the smear is delayed it resembles reverb.
This is exactly what a poor implementation of an mpeg encoder
would produce.
I've included a sample program code to
illustrate audio programming here.
It show the basics of opening an OSS audio device in full duplex
with open and
ioctl.
There's also example use of a POSIX timer and some simple FFT
code. It tries
to remove noise by parabolically cutting frequency spectra below a
certain threshold in real time. Bump the cutoff
threshold up a few orders of magnitude and you get those "fading"
artifacts.
Some "code in process" that tries to
remap frequencies (heterodyning) in realtime is here,
but it's not pretty.
Here are some examples of the
heterodyne work, sorry but they are low volume:
Piano
with remapping from 100 bins above
Piano
with sqrt of 2 remapping
Square
root remapping-flameco guitar
Square
root regular guitar
Square
root horns and strings
Cheesy
synth to the 3.1 power
All materials © 2002-2010 Jason Downer