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audioconvert: tweak resampler window some more

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By: Kevin Yin

R->A calculation removed: it wasn't valid anyway. No behavior change.
Placed existing A in there directly.

cosh window -> strangely tweaked exp window: remove the discontinuity
at the border, which is wrong for a window function. If A changes in the
future, this window will be better. With the current A, you will not be
able to tell the difference on any graph. (Of course, it's not a cosh
window anymore.)

Fixes #2574
This commit is contained in:
Wim Taymans 2022-07-20 10:18:47 +02:00
parent 5a8af97a40
commit 0bf7911b37
1 changed files with 4 additions and 3 deletions
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7
spa/plugins/audioconvert/resample-native.c
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@ -68,14 +68,15 @@ static inline double window_blackman(double x, double n_taps)
}
static inline double window_cosh(double x, double n_taps)
{
double R = 190.0, r;
double A = (-325.1E-6 * R + 0.1677) * R - 3.149;
double r;
double A = 16.97789;
double x2;
x = 2.0 * x / n_taps;
x2 = x * x;
if (x2 >= 1.0)
return 0.0;
r = cosh(A * sqrt(1 - x2)) / cosh(A);
/* doi:10.1109/RME.2008.4595727 with tweak */
r = (exp(A * sqrt(1 - x2)) - 1) / (exp(A) - 1);
return r;
}