[sdiy] jitter in oscillators for music purposes

[Scott Gravenhorst]

This is getting interesting.  Is the Chameleon capable of this sort of thing
(spoke by a person who would love to get one when money finally becomes
something I can count)?

"Sean Costello" <seancostello2003 at comcast.net> wrote:
>Well, you can hear the sweeping of the partials up in down in various
>virtual analog synths. Reaktor, for example, as well as the Pro-52 from
>Native Instruments (the Pro-53 has reduced aliasing, but it is still there).
>My guess is that a fair number of virtual analogs use oversampling, and
>accept the aliasing produced in order to have the flexibility of waveform
>generation (pulse width modulation, variable slope, etc., are all fairly
>easy).
>
>As far as a simple approximation, how about adding noise directly to the
>phase increment value? This will give you phase modulation, as well as a
>small amount of amplitude modulation (due to the fact that the current phase
>+ phase increment + noise may wrap around, whereas current phase + phase
>increment would not).
>
>I am interested to hear about the perceptual effects of the precise
>simulation of jitter in the oscillator. However, once the perceptual effects
>have been worked out, it seems like it would make sense to try approximating
>the effects with a simpler noise function, in order to be able to use the
>results in a real-time analog synth emulator.
>
>Sean Costello
>
>----- Original Message ----- 
>From: "Czech Martin" <Martin.Czech at Micronas.com>
>To: "Sean Costello" <seancostello2003 at comcast.net>; "Antti Huovilainen"
><ajhuovil at cc.hut.fi>
>Cc: "Colin f" <colin at colinfraser.com>; <synth-diy at dropmix.xs4all.nl>
>Sent: Friday, July 16, 2004 1:07 AM
>Subject: RE: [sdiy] jitter in oscillators for music purposes
>
>
>> The partials of a saw wave do not really fade out soon.
>> the 1/N law is tranlated into -20log10(N), the 100th will thus
>> have only -40db attenuation. As long as they stay where they are,
>> this doesn't matter. If they are wrapped arround by aliasing,
>> it will become very obvious.
>>
>> If the tone sweeps up, the reflected partials will sweep down.
>> Very ugly.
>>
>> The problem here is not to create a table based cyclical
>> waveform by band limited synthesis.
>>
>> The problem is to compute a saw core PLUS noise,
>> in order to get the jitter. This is not ADDING noise
>> in a linear fashion, but this pesky phase + amplitude modulation
>> business with high bandwidth noise. After that is done precisely,
>> bandwidth will of course be reduced to play back the result.
>> That means that a (very simple) equation solver has to be set up,
>> with sufficient small time step, this step size can reach from
>> 1us to 1ns, depending on the asctual error.
>> After that 1st band limiting and equidistant sampling.
>> After that downsampling to something reasonable.
>>
>>
>> m.c.
>>
>> > -----Original Message-----
>> > From: Sean Costello [mailto:seancostello2003 at comcast.net]
>> > Sent: Donnerstag, 15. Juli 2004 21:32
>> > To: Antti Huovilainen; Czech Martin
>> > Cc: Colin f; synth-diy at dropmix.xs4all.nl
>> > Subject: Re: [sdiy] jitter in oscillators for music purposes
>> >
>> >
>> > 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
>> >
>> >
>>
>

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