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

[Adrian Godwin]

Interesting idea. I would think that the minimal perceptible change (5ms in
your delay example) might map to the time spent at an unexpected frequency
and there would also be a significant parameter in the size of the
frequency error. The measurement of wow and flutter in tape recordings
might provide some benchmarks.

The ideal equipment would be an audio signal generator with the ability to
FM modulate. I have an HP3312A function generator that includes a modulator
source and many others would provide something similar.

It should be possible to construct suitable test sound files and play them
on a computer, but for experimentation it might be better to modify the
frequency in real time. This might be done with an arduino - here's the
basics of a player for .wav files that might be modified for an
adjustable playback rate, or you might just use tone generator code with
continual small variations to the frequency.

https://www.instructables.com/Audio-Player-Using-Arduino-With-Micro-SD-Card/
https://docs.arduino.cc/built-in-examples/digital/toneMelody




On Wed, Oct 18, 2023 at 12:31 PM 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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