Yes it's related, I dont recall if I used one of these filters
in my first implementation which was several years ago.
I used a complex filter before I used the SVF and AP.

But I think you can't do full phase modulation with such filters?
I think that was my motivation to apply the rotation outside of the filter.

Either way it seems lighter on cpu when you use the external rotation with
parabolas instead of trig operations since you dont have to constantly
adapt the internal state of the filter.

A drawback of the method in general with either filter is that
you can cancel the internal state with an impulse.

I havent figured out what the best excitation signal is.

The paper you linked suggests to delay the impulse until a zero crossing
but that is not an option in my use cases.


Am 03.04.2018 um 01:46 schrieb Corey K:
Your idea seems to bear a few similarities to this (just in case you haven't seen it already): https://ccrma.stanford.edu/~jos/smac03maxjos/ <https://ccrma.stanford.edu/%7Ejos/smac03maxjos/>



On Mon, Apr 2, 2018 at 2:46 PM, gm <g...@voxangelica.net <mailto:g...@voxangelica.net>> wrote:


    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) output
    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 more efficiently
    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 signal,
    the difference is really very small sonically, since the modulator
    is still sine
    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
    filter cutoff.
    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:
    https://soundcloud.com/traumlos_kalt/smoke-piano-test-1-01/s-W54wz
    <https://soundcloud.com/traumlos_kalt/smoke-piano-test-1-01/s-W54wz>

    I wonder if this idea is new?

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