[sdiy] jitter in oscillators for music purposes

[Sean Costello]

Rumor has it that the Clavia synths just run their saws, squares, etc., at
the output sampling rate of 96 kHz, and that no oversampling is used. The
reason that this might work is that the harmonics of a sawtooth that are
above 48 KHz will probably have insignificant amplitude, depending on the
frequency of the sawtooth. The Nord Modular also has a control rate running
at 1/4 the sampling rate, which suggests that they are working with vectors
of samples, as opposed to generating audio on a sample-by-sample basis.

If you are working with a computer, oversampling is probably a necessity,
assuming you want to generate native waveforms, as opposed to using BLIT, or
crossfading between single cycle samples. However, a hardware DSP system can
use a higher output sampling rate, which gives you more headroom (in Hz) for
the harmonics to die away to a reasonable amplitude. Or, you  could use
oversampling, but with lower oversampling ratios and less steep filters
(i.e. lower order filters).

Sean Costello

----- Original Message ----- 
From: "Antti Huovilainen" <ajhuovil at cc.hut.fi>
To: "Czech Martin" <Martin.Czech at Micronas.com>
Cc: "Colin f" <colin at colinfraser.com>; <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, July 14, 2004 5:45 AM
Subject: RE: [sdiy] jitter in oscillators for music purposes


> On Mon, 12 Jul 2004, Czech Martin wrote:
>
> > But the creation of saws via discrete *integration*
> > will create some alias as well....
>
> Here using minblep / blit should help. Google for icmc01-hardsync.pdf and
> blit.pdf
>
> > I wonder if oversampling will help a lot...
>
> Oversampling helps around 12dB/octave (one times 6dB before aliasing and
> another 6dB after aliasing since the oversampled part of alias is filtered
> away). I'd suggest combination of minblep/blit and oversampling.
>
> Antti
>
> Give a man a fire, and he'll be warm that day,
> Set him alight and he'll be warm for the rest of his life