[sdiy] Moogey jitter

[David Cornutt]

I programmed an emulation of a sawtooth oscillator in Csound.
The basic algorithm is pretty simple:

1.  Set output variable to minimum value
2.  Output a sample
3.  Add a fixed increment to the output variable
4.  If the fixed increment is < the reset value, go to step 1.
5.  Compute a random inc/dec value within a specified range and add to 
the reset value
6.  Go to step 1

Using an output start value of -15000, and an initial reset value of 
+15000,
and an output increment of 60, I get a (rather steep) sawtooth at 88.2 
Hz.
I ran a score generating the tone four times, each with a different 
random-walk
value for the reset point.  Each tone is 10 seconds long, and they are
separated by one second of silence.  The file is an uncompressed WAV
(3.6 Mbytes) at:

http://home.hiwaay.net/~cornutt/Music/Web%20Page/sawtooth1.wav

The random-walk for the four tones are:

Tone 1: zero deviation.  I put this in as a baseline.
Tone 2: 0.076% max deviation.
Tone 3: 0.153% max deviation
Tone 4: 0.229% max deviation

To make the effect more apparent, I did a second run where tones 2-4
are each mixed with tone 1.  You can definitely hear the phasing:

http://home.hiwaay.net/~cornutt/Music/Web%20Page/sawtooth1a.wav

Note that I used a constant seed for the random-number generator, so all
four tones use the same basic pseudo-random sequence as the basis for
their random walks.  This is apparent when you listen to the phased 
tones.

Result: When I listen to it, I *think* I can hear something happening 
in tone 2.
Maybe not; if I were listening to tones 1 and 2 in a double-blind test, 
I'm not
sure I could sort them out.  However, I can definitely hear something 
happening
in tone 3, and in tone 4 I can start to pick out pitch deviations.   (I 
was surprised
at how little deviation resulted in audible artifacts.)  However, I 
would
not in any case describe the effect as "phat" or "warm".  In fact, I'm 
not quite sure
how I would describe it -- it's sort of like that feeling you get when 
you think you
were supposed to remember to do something, but you can't recall what it 
is.