[sdiy] Analysis of frequency variation in analogue synths

[Richard Wentk]

On 3 May 2007, at 12:39, Colin f wrote:

>
> The important question for me is, "does a single oscillator  
> minimoog patch
> sound 'analogue' ?".
> To which the answer is a resounding yes.
> But if I can't hear any extra 'analogueness' in the raw oscillator  
> compared
> to a single-cycle sample of it for the typical duration of a note  
> played on
> the synth, surely that means other factors have a much more important
> influence on analogueness than oscillator jitter ?

Yes, but all you're doing is eliminating one particular factor.  
Analogueness is likely to be a combination of factors, rather than a  
single one - possibly a synergistic combination which is greater than  
the sum of its parts.

I find that on softsynths, a single digital oscillator usually sounds  
weedy. But some softsynths have a multiple mode which stacks the  
voices so you get 8 or 16 or however many it is, per note. Once you  
do that, the sound fills out nicely and is certainly more 'analogue'  
than a single oscillator.

> Clearly things will be different with a two oscillator sound.
> A worthwhile test there would be to see if you can pick out a pair  
> of real
> analogue oscillators in unison, against a pair of samples in unison  
> where
> the sampled oscillators have small amounts of random modulation.

That would depend on the kind of modulation.

I think the real thing is a combination of:

1/f noise in the background
Poor s/n ratio
Limited or uneven frequency response (hardly any vintage analogue  
gear has a flat 20-20 frequency response)
Jitter
Wander
Waveshape variation with frequency and perhaps temperature
Sync locking effects
Noise burst effects and hysteresis
Distortion - of many different sorts
CV breakthrough effects, which can make envelopes sound like they  
have an extra kick
Non-textbook envelope and LFO curves

And there will be no digital:

Splashy phase shifts at the top end
Quantisation noise
Aliasing
...and other nasties that contribute to that crunchy grainy digital  
sound that seems almost inevitable when working at 44.1.

What makes it complicated is that each item on the list has enough  
potential detail to spawn a few PhDs.

As an aside - it's a classic case of reality being much more  
complicated than the usual models. *Accurately* modelling analogue  
behaviour is light years away from putting a digital sawtooth through  
a digital SVF and using digital envelopes and LFOs for modulation.

Richard