[sdiy] quadrature sine wave oscillator question

[jhaible at debitel.net]

> I'm not sure if we are talking about the same thing...

I am sure we are.

> In the moment I'm not talking about frequency control,
> this can be done via pots or multipliers, as you say.

Two 2Q multipliers for frequency control, plus two
4Q multipliers for (Asin(wt))**2 + (Acos(wt))**2,
plus (maybe) one more multiplier for SQRT of the above.
(Probably the SQRT is not necessary).


> I'm talking about the possibility to derive INSTANTANEOUS
> amplitude information out of such a quadrature thing.
> All other sine wave designs get a very much delayed information
> on amplitude (i.e. peak detector and LPF).

Yes. But here, we have (theoretically) no delay, as we can
get the amplitude information instantly from evaluating
the sin and cos term.

But what if (at startup, or due to mismatch), we don't
have exact sin / cos functions ? If it's Asin() and Bcos()
with A != B ? Will it still work ?
I fear there might be too much precision required to give
an unexpensive alternative to the waveshaper approach.

(But I have *not* followed this any further, so I'd be
pleased to learn if it's a good practical solution really ..)

JH.

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