[sdiy] jitter analysis

[Fredrik Carlqvist]

> But another question : are there any dependencies between 
> the measured standard deviation (SD) of succeeding time 
> intervals (of each oscillator cycle) and the frequency 
> of the oscillator ? I.e., low frequency -> high SD, high 
> frequency -> low SD ? 
 
Some of the oscillators show this kind of frequency dependency. I think this
is because the current in the expco gets very low on low frequencies. The
noise then gets proportionally larger. Some VCOs don't show this behavior,
they have the same jitter (measured in SD) on all frequencies. 

> And, yet another question : if 44.100 Hz are much too low 
> to measure this jitter : why can this jitter be audible 
> (and responsible for "warmer" sounds perhaps) on CD, with 
> this sampling rate ? Or do you think, it _IS_ not audible 
> on CD, but only when you hear the synth beeing played life?

Well, this is what I am trying to find out. My hypothesis is that the sound
gets fuller with jitter. I think that physical instruments produce both
jitter and phase distortion. Think of the violin, the tone is produced by
friction between the bow and the string. It just cannot have zero SD. And
physical sounds are what the ear is designed for.

When sampling a tone, the jitter comes along too, but not perfectly. It is
not possible to measure the jitter with any precision after sampling it at
44100Hz. Also, I think most of the psychological effects of the jitter are
lost when sampling. It is often easy to here the difference between a cello
played live and one recorded on a CD.

I have contacts with some perception psychologists on the University of
Uppsala and KTH. After the summer, I will contact them to hear what they
have to say. 


Fredrik C