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

[Alwyn Lloyd]

Hi Tom,

>
> 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.

Interesting idea..

If you have a digital synth available, or another very stable frequency 
source available, could you perhaps record the analog oscillator into one 
channel, and then the "stable reference" into another?

That would at least give you an idea of if there are any variations due to 
the recording process..


Cheers,
Alwyn


>
> Regards,
> Tom
>
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