mirror of https://github.com/mpv-player/mpv
204 lines
5.1 KiB
C
204 lines
5.1 KiB
C
/*=============================================================================
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//
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// This software has been released under the terms of the GNU General Public
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// license. See http://www.gnu.org/copyleft/gpl.html for details.
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//
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// Copyright 2001 Anders Johansson ajh@atri.curtin.edu.au
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//
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//=============================================================================
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*/
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/* Calculates a number of window functions. The following window
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functions are currently implemented: Boxcar, Triang, Hanning,
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Hamming, Blackman, Flattop and Kaiser. In the function call n is
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the number of filter taps and w the buffer in which the filter
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coefficients will be stored.
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*/
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#include <math.h>
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#include "dsp.h"
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/*
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// Boxcar
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//
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// n window length
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// w buffer for the window parameters
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*/
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void af_window_boxcar(int n, _ftype_t* w)
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{
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int i;
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// Calculate window coefficients
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for (i=0 ; i<n ; i++)
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w[i] = 1.0;
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}
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/*
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// Triang a.k.a Bartlett
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//
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// | (N-1)|
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// 2 * |k - -----|
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// | 2 |
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// w = 1.0 - ---------------
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// N+1
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// n window length
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// w buffer for the window parameters
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*/
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void af_window_triang(int n, _ftype_t* w)
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{
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_ftype_t k1 = (_ftype_t)(n & 1);
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_ftype_t k2 = 1/((_ftype_t)n + k1);
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int end = (n + 1) >> 1;
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int i;
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// Calculate window coefficients
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for (i=0 ; i<end ; i++)
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w[i] = w[n-i-1] = (2.0*((_ftype_t)(i+1))-(1.0-k1))*k2;
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}
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/*
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// Hanning
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// 2*pi*k
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// w = 0.5 - 0.5*cos(------), where 0 < k <= N
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// N+1
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// n window length
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// w buffer for the window parameters
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*/
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void af_window_hanning(int n, _ftype_t* w)
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{
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int i;
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_ftype_t k = 2*M_PI/((_ftype_t)(n+1)); // 2*pi/(N+1)
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// Calculate window coefficients
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for (i=0; i<n; i++)
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*w++ = 0.5*(1.0 - cos(k*(_ftype_t)(i+1)));
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}
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/*
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// Hamming
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// 2*pi*k
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// w(k) = 0.54 - 0.46*cos(------), where 0 <= k < N
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// N-1
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//
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// n window length
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// w buffer for the window parameters
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*/
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void af_window_hamming(int n,_ftype_t* w)
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{
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int i;
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_ftype_t k = 2*M_PI/((_ftype_t)(n-1)); // 2*pi/(N-1)
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// Calculate window coefficients
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for (i=0; i<n; i++)
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*w++ = 0.54 - 0.46*cos(k*(_ftype_t)i);
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}
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/*
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// Blackman
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// 2*pi*k 4*pi*k
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// w(k) = 0.42 - 0.5*cos(------) + 0.08*cos(------), where 0 <= k < N
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// N-1 N-1
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//
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// n window length
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// w buffer for the window parameters
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*/
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void af_window_blackman(int n,_ftype_t* w)
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{
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int i;
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_ftype_t k1 = 2*M_PI/((_ftype_t)(n-1)); // 2*pi/(N-1)
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_ftype_t k2 = 2*k1; // 4*pi/(N-1)
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// Calculate window coefficients
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for (i=0; i<n; i++)
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*w++ = 0.42 - 0.50*cos(k1*(_ftype_t)i) + 0.08*cos(k2*(_ftype_t)i);
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}
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/*
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// Flattop
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// 2*pi*k 4*pi*k
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// w(k) = 0.2810638602 - 0.5208971735*cos(------) + 0.1980389663*cos(------), where 0 <= k < N
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// N-1 N-1
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//
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// n window length
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// w buffer for the window parameters
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*/
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void af_window_flattop(int n,_ftype_t* w)
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{
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int i;
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_ftype_t k1 = 2*M_PI/((_ftype_t)(n-1)); // 2*pi/(N-1)
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_ftype_t k2 = 2*k1; // 4*pi/(N-1)
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// Calculate window coefficients
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for (i=0; i<n; i++)
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*w++ = 0.2810638602 - 0.5208971735*cos(k1*(_ftype_t)i) + 0.1980389663*cos(k2*(_ftype_t)i);
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}
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/* Computes the 0th order modified Bessel function of the first kind.
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// (Needed to compute Kaiser window)
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//
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// y = sum( (x/(2*n))^2 )
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// n
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*/
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#define BIZ_EPSILON 1E-21 // Max error acceptable
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static _ftype_t besselizero(_ftype_t x)
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{
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_ftype_t temp;
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_ftype_t sum = 1.0;
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_ftype_t u = 1.0;
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_ftype_t halfx = x/2.0;
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int n = 1;
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do {
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temp = halfx/(_ftype_t)n;
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u *=temp * temp;
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sum += u;
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n++;
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} while (u >= BIZ_EPSILON * sum);
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return(sum);
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}
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/*
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// Kaiser
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//
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// n window length
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// w buffer for the window parameters
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// b beta parameter of Kaiser window, Beta >= 1
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//
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// Beta trades the rejection of the low pass filter against the
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// transition width from passband to stop band. Larger Beta means a
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// slower transition and greater stop band rejection. See Rabiner and
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// Gold (Theory and Application of DSP) under Kaiser windows for more
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// about Beta. The following table from Rabiner and Gold gives some
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// feel for the effect of Beta:
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//
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// All ripples in dB, width of transition band = D*N where N = window
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// length
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//
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// BETA D PB RIP SB RIP
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// 2.120 1.50 +-0.27 -30
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// 3.384 2.23 0.0864 -40
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// 4.538 2.93 0.0274 -50
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// 5.658 3.62 0.00868 -60
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// 6.764 4.32 0.00275 -70
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// 7.865 5.0 0.000868 -80
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// 8.960 5.7 0.000275 -90
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// 10.056 6.4 0.000087 -100
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*/
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void af_window_kaiser(int n, _ftype_t* w, _ftype_t b)
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{
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_ftype_t tmp;
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_ftype_t k1 = 1.0/besselizero(b);
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int k2 = 1 - (n & 1);
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int end = (n + 1) >> 1;
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int i;
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// Calculate window coefficients
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for (i=0 ; i<end ; i++){
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tmp = (_ftype_t)(2*i + k2) / ((_ftype_t)n - 1.0);
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w[end-(1&(!k2))+i] = w[end-1-i] = k1 * besselizero(b*sqrt(1.0 - tmp*tmp));
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}
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}
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