I don't know if this idea is new, I had it for some time but have never
seen it mentioned anywhere:
Use a filter with high q and rotate it's (complex) output by the (real)
of another filter to obtain a phase modulated sine wave.
Excite with an impulse or impact signal.
It's basically crossed between modal and phase modulation synthesis.
Now there are some ideas to this to make it practical and a useful
substitute for phase modulation and FM:
You can use a state variable filter with an additional allpass instead of
the complex filter to obtain a filter you can pitch modulate in audio
(useful for drum synthesis ect) (or maybe the 90 shift can be designed
into the SVF IDK.)
Instead of expensive trig calculations for the rotation, or using
the normalized complex signal form the other filter (also expensive)
just use a very coarse parabolic sine/cosine approximation and the real
the difference is really very small sonically, since the modulator is
and the radius stays around 1 so it's the effect of a small amplitude
modulation on the modulator
caused by the slight deviation of the circle.
I couldnt tell the difference when I tested it first.
You need 7 mults and 4 adds in addition to the SVF for the AP and
rotation per carrier.
But you save an envelope for each operator and have a pretty efficient
sine operator with the SVF.
And you get all the benfits of phase modulation over frequency
modulation of the
It's very useful for drum synthesis but also useful for some other
percussive sounds like "FM" pianos etc.
Here is an audio demo, with cheap "soundboard" and some other fx added:
I wonder if this idea is new?
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