Yet some more phasemodulation thoughts

[Harry Bissell]

the only places I've seen stagger-tuned phase shift networks is in the National
Semi Audio Apps. handbook, and (I think) the Uni-vibe. Most designs use the same
values, just adding stages for more depth...

I use the same values... and other DIY-ers use ????

:^) Harry

mbartkow at ET.PUT.Poznan.PL wrote:

> Why not use phase shifters for this job ?
>
> Lets consider a series of OTA-based phase shifters. These have such
> advantage over others that can be linearly tuned within a wide fre-
> quency range. Applying the same control voltage as one going to VCO
> input one achieves a phase shift that is constant over pitch changes
> of the VCO. Now modulating the PS control voltage by the audio signal
> the phase of the signal is modulated as desired for the Yammy (or should
> I spell it "yummy" ?) sound :-)
>
> The number of phase shift stages certainly determines the maximum
> modulation depth. I don't know yet, if it is better to tune the particular
> sections to different "center" frequencies (i.e. the frequency where the
> phase shift of the stage is pi/2), which would allow to achieve more linear
> phase/frequency characteristics and more linear phase shift dependence on
> the modulation input. On the other hand, if phase shift depends linearly
> on the frequency it is just a continuous delay line. So maybe a step-like
> phase characteristics is better, whereby all the spectral components are
> shifted in the same way ? This is easier to build, but the shape of the
> signal is destroyed as in all nonlinear-phase systems. It might lead to
> more dramatic effect of the modulation. What do you think?
>
> regards,
>
> MB
>
> PS. I have got a reprint of the original J. Chowning's article on FM synthesis.
> Although he refers to it as "frequency modulation", it is obviously a phase
> modulation in his own formulas. In fact, these two are to some extent equiv-
> alent, since after appropriate scalling of the modulation depth, or index they
> give identical output.
>
> --
>
> Maciej Bartkowiak, PhD
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