[sdiy] Analogue Drift (was Re: HF VCOs and tracking problems)

[Tom Wiltshire]

On 13 Nov 2012, at 23:32, Richie Burnett wrote:

> Great as a reference for characterising the drift of analogue synth VCOs, but I digress...

Have you managed to get any decent data for this, Richie?

I had a go using a friend's 24-bit 192-KHz audio interface to record files which I then analysed post-recording with the computer. I was hoping to get enough data to allow me to generate a realistic "drift waveform" for a given synth or oscillator, but I never got very far with it. I wasn't convinced that the results I got weren't just artefacts of the process rather than actual data. The expectation is that analog oscillators vary from "true" pitch by some slowly varying random amount, like a heavily-filtered noise signal or random walk or something, but whilst I've heard these effects posited on forums a million times, I've never actually seen anyone who has got the data to back up the supposition. I had a go and didn't manage to get it either.
Generating different types of (pseudo)random waveform isn't hard - the question is which is most suitable for the effect we're trying to get. In the end, I just designed a module that could generate loads of different types of randomness and left it to the user - make your oscs wobbly if you want, don't if you don't.

Regards,
Tom