I'm really looking forward to testing the dynamic waveshaping opcodes. It is
something I've thought about trying to do in csound, but never gotten around
to actually coding. Nice.
Oeyvind


2007/12/5, Anthony Kozar <anthonykozar@sbcglobal.net>:
>
> Victor.Lazzarini@nuim.ie wrote on 12/5/07 2:54 AM:
>
> > PD seem useful. UDOs are also good because they're didactical, can you
> > do both?
>
> Thanks.  I wrote the phase dist. opcodes (and powershape below) a while
> ago
> but I will make UDOs too.
>
> > How do the waveshaping opcodes you mention
> > differ from simply building them with oscillator and table
> > lookup?
>
> They allow for _dynamic_ waveshaping where the transfer function varies
> over
> time.  I have written the following opcodes so far and hope to come up
> with
> some more:
>
> aout  powershape    ain, kShapeAmount [, ifullscale]
> aout  polynomial    ain, ka0 [, ka1 [, ka2 [...]]]
> aout  chebyshevpoly ain, ka0 [, ka1 [, ka2 [...]]]
>
> polynomial efficiently calculates any single-variable polynomial with
> k-rate
> coefficients.  chebyshevpoly does the same but each coefficient is a
> multiplier for an nth-order chebyshev polynomial.  With a sine wave input,
> this allows precise time-varying control over any number of
> harmonically-tuned partials, but requires only one oscillator.
>
> Manual description for powershape:
>
> This opcode is very similar to the pow unit generators that already exist
> in
> Csound for calculating the mathematical "power of" operation.  However, it
> introduces a couple of twists which I think make it much more useful for
> waveshaping audio-rate signals.  The kShapeAmount parameter is the
> exponent
> to which the input signal is raised.
>
> Normally, unless the exponent is an odd integer, the pow() of a negative
> input is a complex number, so the Csound ugens simply return zero in those
> cases.  This will turn a bipolar audio signal into a unipolar signal with
> large portions of the output pinned to zero.  The powershape opcode
> instead
> treats all input values as positive but preserves their sign in the output
> signal.  This allows for smooth shaping of any input signal while varying
> the exponent over any range.  (Powershape also (hopefully) deals
> intelligently with  discontinuities that could arise when the exponent and
> input are both zero.  Note though that negative exponents will usually
> cause
> the signal to exceed the maximum amplitude specified by the ifullscale
> parameter and should normally be avoided).
>
> The other adaptation involves the ifullscale parameter.  The input signal
> is
> divided by ifullscale before being raised to kShapeAmount and then
> multiplied by ifullscale before being output.  This normalizes the input
> signal to the interval [-1,1], guaranteeing that the output will also be
> within this range.  Also, the pow() function provides a smoothly evolving
> transfer function when its input is in this range.  Values of kShapeAmount
> between (0,1) will make the signal more "convex" while values greater than
> 1
> will make it more "concave" and a value of exactly 1.0 will produce no
> change in the input signal.
>
>
> Anthony Kozar
> anthonykozar AT sbcglobal DOT net
> http://anthonykozar.net/
>
>
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