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Diffstat (limited to 'audio/filter/window.c')
-rw-r--r-- | audio/filter/window.c | 213 |
1 files changed, 213 insertions, 0 deletions
diff --git a/audio/filter/window.c b/audio/filter/window.c new file mode 100644 index 0000000000..a970bdcbea --- /dev/null +++ b/audio/filter/window.c @@ -0,0 +1,213 @@ +/* + * Copyright (C) 2001 Anders Johansson ajh@atri.curtin.edu.au + * + * This file is part of MPlayer. + * + * MPlayer is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * MPlayer is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with MPlayer; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + */ + +/* Calculates a number of window functions. The following window + functions are currently implemented: Boxcar, Triang, Hanning, + Hamming, Blackman, Flattop and Kaiser. In the function call n is + the number of filter taps and w the buffer in which the filter + coefficients will be stored. +*/ + +#include <math.h> +#include "dsp.h" + +/* +// Boxcar +// +// n window length +// w buffer for the window parameters +*/ +void af_window_boxcar(int n, FLOAT_TYPE* w) +{ + int i; + // Calculate window coefficients + for (i=0 ; i<n ; i++) + w[i] = 1.0; +} + + +/* +// Triang a.k.a Bartlett +// +// | (N-1)| +// 2 * |k - -----| +// | 2 | +// w = 1.0 - --------------- +// N+1 +// n window length +// w buffer for the window parameters +*/ +void af_window_triang(int n, FLOAT_TYPE* w) +{ + FLOAT_TYPE k1 = (FLOAT_TYPE)(n & 1); + FLOAT_TYPE k2 = 1/((FLOAT_TYPE)n + k1); + int end = (n + 1) >> 1; + int i; + + // Calculate window coefficients + for (i=0 ; i<end ; i++) + w[i] = w[n-i-1] = (2.0*((FLOAT_TYPE)(i+1))-(1.0-k1))*k2; +} + + +/* +// Hanning +// 2*pi*k +// w = 0.5 - 0.5*cos(------), where 0 < k <= N +// N+1 +// n window length +// w buffer for the window parameters +*/ +void af_window_hanning(int n, FLOAT_TYPE* w) +{ + int i; + FLOAT_TYPE k = 2*M_PI/((FLOAT_TYPE)(n+1)); // 2*pi/(N+1) + + // Calculate window coefficients + for (i=0; i<n; i++) + *w++ = 0.5*(1.0 - cos(k*(FLOAT_TYPE)(i+1))); +} + +/* +// Hamming +// 2*pi*k +// w(k) = 0.54 - 0.46*cos(------), where 0 <= k < N +// N-1 +// +// n window length +// w buffer for the window parameters +*/ +void af_window_hamming(int n,FLOAT_TYPE* w) +{ + int i; + FLOAT_TYPE k = 2*M_PI/((FLOAT_TYPE)(n-1)); // 2*pi/(N-1) + + // Calculate window coefficients + for (i=0; i<n; i++) + *w++ = 0.54 - 0.46*cos(k*(FLOAT_TYPE)i); +} + +/* +// Blackman +// 2*pi*k 4*pi*k +// w(k) = 0.42 - 0.5*cos(------) + 0.08*cos(------), where 0 <= k < N +// N-1 N-1 +// +// n window length +// w buffer for the window parameters +*/ +void af_window_blackman(int n,FLOAT_TYPE* w) +{ + int i; + FLOAT_TYPE k1 = 2*M_PI/((FLOAT_TYPE)(n-1)); // 2*pi/(N-1) + FLOAT_TYPE k2 = 2*k1; // 4*pi/(N-1) + + // Calculate window coefficients + for (i=0; i<n; i++) + *w++ = 0.42 - 0.50*cos(k1*(FLOAT_TYPE)i) + 0.08*cos(k2*(FLOAT_TYPE)i); +} + +/* +// Flattop +// 2*pi*k 4*pi*k +// w(k) = 0.2810638602 - 0.5208971735*cos(------) + 0.1980389663*cos(------), where 0 <= k < N +// N-1 N-1 +// +// n window length +// w buffer for the window parameters +*/ +void af_window_flattop(int n,FLOAT_TYPE* w) +{ + int i; + FLOAT_TYPE k1 = 2*M_PI/((FLOAT_TYPE)(n-1)); // 2*pi/(N-1) + FLOAT_TYPE k2 = 2*k1; // 4*pi/(N-1) + + // Calculate window coefficients + for (i=0; i<n; i++) + *w++ = 0.2810638602 - 0.5208971735*cos(k1*(FLOAT_TYPE)i) + + 0.1980389663*cos(k2*(FLOAT_TYPE)i); +} + +/* Computes the 0th order modified Bessel function of the first kind. +// (Needed to compute Kaiser window) +// +// y = sum( (x/(2*n))^2 ) +// n +*/ +#define BIZ_EPSILON 1E-21 // Max error acceptable + +static FLOAT_TYPE besselizero(FLOAT_TYPE x) +{ + FLOAT_TYPE temp; + FLOAT_TYPE sum = 1.0; + FLOAT_TYPE u = 1.0; + FLOAT_TYPE halfx = x/2.0; + int n = 1; + + do { + temp = halfx/(FLOAT_TYPE)n; + u *=temp * temp; + sum += u; + n++; + } while (u >= BIZ_EPSILON * sum); + return sum; +} + +/* +// Kaiser +// +// n window length +// w buffer for the window parameters +// b beta parameter of Kaiser window, Beta >= 1 +// +// Beta trades the rejection of the low pass filter against the +// transition width from passband to stop band. Larger Beta means a +// slower transition and greater stop band rejection. See Rabiner and +// Gold (Theory and Application of DSP) under Kaiser windows for more +// about Beta. The following table from Rabiner and Gold gives some +// feel for the effect of Beta: +// +// All ripples in dB, width of transition band = D*N where N = window +// length +// +// BETA D PB RIP SB RIP +// 2.120 1.50 +-0.27 -30 +// 3.384 2.23 0.0864 -40 +// 4.538 2.93 0.0274 -50 +// 5.658 3.62 0.00868 -60 +// 6.764 4.32 0.00275 -70 +// 7.865 5.0 0.000868 -80 +// 8.960 5.7 0.000275 -90 +// 10.056 6.4 0.000087 -100 +*/ +void af_window_kaiser(int n, FLOAT_TYPE* w, FLOAT_TYPE b) +{ + FLOAT_TYPE tmp; + FLOAT_TYPE k1 = 1.0/besselizero(b); + int k2 = 1 - (n & 1); + int end = (n + 1) >> 1; + int i; + + // Calculate window coefficients + for (i=0 ; i<end ; i++){ + tmp = (FLOAT_TYPE)(2*i + k2) / ((FLOAT_TYPE)n - 1.0); + w[end-(1&(!k2))+i] = w[end-1-i] = k1 * besselizero(b*sqrt(1.0 - tmp*tmp)); + } +} |