[sdiy] super cheap synthisizers

[Ingo Debus]

harry wrote:
> 
> I would NOT assume that you could make one pulse 'shorter' and one 'longer'...
> if you did it evenly... it would sound like a pulse of 1/2 the frequency you intended...
> with a non 50% duty cycle...
> 
> If it was a random 'short-long' it would sound like sh!t.  (well to be fair... I am known
> for saying things sound like sh!t that some folks like...).  This would be 'jitter' in the
> frequency and would not be a good feature.. OK to add it if you want 'that' sound..
> but if you could not avoid it... really bad.

Isn't that more or less what the phase accumulator oscillator does? As I
understand it, it runs at a fixed sampling rate, regardless of the
oscillator frequency. Given the values used are precise enough (someone
here wrote 24 bit) it will try to keep the frequency as precise as
possible; but since the output is only updated at the sampling frequency
the period time is sometimes one sample longer, if the sampling rate is
not exactly an integer multiple of the output frequency. Sort of jitter,
correct? (Probably not random.)

Is this the reason why Paul Maddox suggests such a high sampling rate, 1
MHz? To keep the jitter low?

Ingo