[sdiy] Analysis of frequency variation in analogue synths

[Nicholas Gregorich]

On Apr 30, 2007, at 4:56 PM, Tom Wiltshire wrote:

> Hello all,
>
> I've just spent an interesting but rather confusing evening trying  
> to analyse the minor variations in frequency that are supposed to  
> account for the 'analogue character' of VCOs. I'm hoping to design  
> a digital oscillator for my monosynth project, and had wondered  
> about trying to include an 'analogue feel' parameter. As a  
> precursor to this, I thought I'd better find out what 'analogue  
> feel' really looks like.
>
> Given that I haven't got a full suite of fancy equipment at my  
> disposal, I sampled some tones from my Pro-One and SH101 into the  
> computer and then looked at the results with software I wrote to  
> analyse sound files. This has its limitations, chief among which is  
> the 44.1KHz (or maybe 48KHz) input sampling of the computer's audio  
> input.

I've thought about measuring VCO jitter too. Does the jitter of the  
ADC have to be measured before assumptions about jitter in the VCO  
signal can me made? Is there an easy way to measure ADC jitter?

What kind of distortion does ADC jitter cause in measuring a pure  
sinusoid anyhow? Is it something you could see measuring a sine at a  
known frequency and doing an FFT?

Nick.