[sdiy] How does a DCO work?

[karl dalen]

> Also note that the 'clock' is a constant rate, not variable. but the
> resulting 'output' is 'effectivly' a variable sample rate. If you, for
> example, do the addition in a micro at a rate of 10Mhz, the output is
> updated every 100nS.
> Even if the frequency output is only 100hz, or if its 10Khz.
> 
> There is a limit on the maximum frequency you can get to before you start
> having to 'drop' samples from your lookup table, but that depends on how you
> impliment the phase accumulator oscillator.
> The Monowave has a limit of around 4Khz before this happens.
> IMHO, anyone who can hear a change in harmonics caused by dropping from 256
> samples to 128 samples when the frequency is over 4Khz should be a in a
> laboratory being studied :-)

However, a phase accumulator osc can jitter!
Ask any Mirage or ESQ1/80 owner! 

Reg
KD