[time-nuts] Re: shoestring budget & jitter AVR328p

[Jim Lux]

I would think that sample timing jitter would look like broadband noise. At least that’s what happens on an ADC - yes, the samples where there’s a large slope (d/dt) the jitter has a larger effect, but I think that “averages out” when looking at many samples. Some individual samples are perturbed more than others.

As for dividing down reducing the jitter, sure - it’s 20 log (N) - just like multiplying up. 


On Mon, 16 Oct 2023 13:11:54 +0200, folkert via time-nuts <time-nuts at lists.febo.com> wrote:

Hello,

As an electronic music-enthousiast I also tinker with sound-chips of
the 8- and 16-bit age. Circuit bending for example. And about that I
have a question.
On my website I published a page describing in a nutshell how tweaking
the clock-frequency of a Philips SAA-1099p soundchip gives interesting
sounds ( https://vanheusden.com/electronics/SAA1099-clock/ ). Here I use
a timer of the Arduino Nano (AVR 328p) as a clock for the SAA1099p
soundchip.
A friend of mine read this and asked me if I have any ideas about the
jitter introduced. Like: if I set the clock to 4MHz, how much jitter
would this give. Now I read somewhere that delays of less than 5ms are
usually not audible but does that also apply to jitter?
First step in the investigation of that is to quantify how much the
jitter introduced is (I guess). I know that when you have a PPS
signal, that you can easily feed that to code that calculates the allan
deviation, but how about clocks in the MHz range? If I divide the clock,
wouldn't that average out any jitter?
My budget is limited and/but I (do) have a hantek DSO-6022BL
oscilloscope, some PicDivs and a 10MHz TCXO.


Regards,

Folkert.
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