[PD] Avoiding clipping with tabread4
czhenry at gmail.com
Mon Aug 25 20:13:30 CEST 2008
On Mon, Aug 25, 2008 at 7:48 AM, PSPunch <shima at pspunch.com> wrote:
> i.e., having a table of [-1 1 1 -1], an index of 1.5 will return 1.25
> with [tabread4]
This is correct. The interpolated values can exceed the values in the
samples. Think about drawing a polynomial through your points, and
where the maximum actually can occur.
> Are there any common practices to avoid unexpected clipping introduced
> by [tabread4] or [tabosc4~] ?
Common practices, not sure. But I think we can establish an upper
bound on the peak value, analytically.
Our polynomial for tabread4~:
So, the maximum value must occur as a function of x between 0 and 1.
Taking our input peak value as 1, the maximum output peak is the sum
of the absolute value of the coefficients of f[-1], f, f, f
x(x-1)(x-2)/6 + (x+1)(x-1)(x-2)/2 - (x+1)x(x-2)/2 - (x+1)x(x-1)/6
= -x^2 + x + 1
vertex: x=1/2, f(1/2) = 1.25
> Further more, under what circumstances (what 4 values referred to) will
> the returned value exceed the range most?
How do you like answering your own questions :) Your example is exactly it.
> Thanks in advance..
> David Shimamoto
> Pd-list at iem.at mailing list
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