[music-dsp] modelling analog drift?

David Lowenfels dfl at alum.mit.edu
Wed Sep 8 15:07:15 EDT 2004

   I'm thinking about how to model analog drift in a synthesizer, and am 
curious to hear what other people think might be important starting 
points. I hope it's not too off-topic. Am I correct to assume that 
analog instability is primarily from thermal fluctuations? Do you think 
a random sample & glide LFO would be satisfactory? I don't have any 
hardware that has this "feature", emulated or not, so I thought I'd see 
what you all would have to say about it.

 From the Alesis Ion manual:
	"An analog synthesizer is a comparatively unstable device. Its 
components tend to be imprecise, never producing a truly constant 
value. Synthesizer enthusiasts call this tendency "drift," and it is 
often cited as a major part  of the difference between the "warm" sound 
of analog synths and the "cold" sound of digital synths. The Ion can 
model the "drifting" behavior of analog synths as well. An Analog Drift 
setting of on will cause the frequencies for each of the oscillators 
and filters per voice to "drift" according to a special algorithm we 
developed. To make the Ion sound even more realistic, they each drift 
independently. Try it; it’s a subtle but very pleasing and effective 

 From an Ion user forum:
	"it should be noted that there is a parameter called analog drift that 
seems to affect pitch and filter settings most obviously and likely has 
some subtle effect on osc waveshapes and envelopes as well.. it does a 
very good job of livening things up and is variable from zero to one 
hundred percent, although turning it all the way up makes the synth 
completely unstable."


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