diff src/window.c @ 107:3e648eec95cb

- Added new helper functions: xtract_windowed() and xtract_features_from_subframes()
- Added windowing functions (window.c)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/window.c	Fri Dec 28 19:34:51 2007 +0000
@@ -0,0 +1,182 @@
+/* libxtract feature extraction library
+ *  
+ * Copyright (C) 2006 Jamie Bullock
+ *
+ * This program 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.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
+ * USA.
+ */
+
+/* window.c: defines window generation functions (formulae courtesy of Wikipedia (http://en.wikipedia.org/wiki/Window_function) */
+
+#include <math.h>
+
+#include "xtract_window_private.h"
+
+void gauss(float *window, const int N, const float sd){
+
+    int n;
+    const float M = N - 1;
+    float num,
+          den,
+          exponent;
+
+    for (n = 0; n < N; n++) {
+
+        num = n - M / 2.f;
+        den = sd * M / 2.f;
+        
+        exponent = -0.5 * powf(num / den, 2);
+
+        window[n] = exp(exponent);
+
+    }
+}
+
+void hamming(float *window, const int N){
+
+    int n;
+    const float M = N - 1;
+
+    for (n = 0; n < N; n++)
+        window[n] = 0.53836 - (0.46164 * cosf(2.0 * PI * (float)n / M));
+
+}
+
+void hann(float *window, const int N){
+
+    int n;
+    const float M = N - 1;
+
+    for (n = 0; n < N; n++)
+        window[n] = 0.5 * (1.0 - cosf(2.0 * PI * (float)n / M));
+
+}
+
+void bartlett(float *window, const int N){
+
+    int n;
+    const float M = N - 1;
+
+    for (n = 0; n < N; n++)
+        window[n] = 2.f / M * (M / 2.f - fabsf(n - M / 2.f));
+
+}
+
+void triangular(float *window, const int N){
+
+    int n;
+    const float M = N - 1;
+
+    for (n = 0; n < N; n++)
+        window[n] = 2.f / N * (N / 2.f - fabsf(n - M / 2.f));
+}
+
+void bartlett_hann(float *window, const int N){
+
+    int n;
+    const float M = N - 1,
+          a0 = 0.62,
+          a1 = 0.5,
+          a2 = 0.38;
+    float term1 = 0.f,
+          term2 = 0.f;
+
+    for (n = 0; n < N; n++){
+
+        term1 = a1 * fabsf(n / M - 0.5);
+        term2 = a2 * cosf(2.0 * PI * (float)n / M);
+
+        window[n] = a0 - term1 - term2;
+    }
+}
+
+void blackman(float *window, const int N){
+
+    int n;
+    const float M = N - 1,
+          a0 = 0.42,
+          a1 = 0.5,
+          a2 = 0.08;
+    float term1 = 0.f,
+          term2 = 0.f;
+
+    for (n = 0; n < N; n++) {
+    
+        term1 = a1 * cosf(2.0 * PI * (float)n / M);
+        term2 = a2 * cosf(4.0 * PI * (float)n / M);
+
+        window[n] = a0 - term1 + term2;
+    }
+}
+
+#define BIZ_EPSILON 1E-21 // Max error acceptable 
+
+/* Based on code from mplayer window.c, and somewhat beyond me */
+float besselI0(float x){
+
+  float temp;
+  float sum   = 1.0;
+  float u     = 1.0;
+  float halfx = x/2.0;
+  int      n     = 1;
+
+  do {
+
+    temp = halfx/(float)n;
+    u *=temp * temp;
+    sum += u;
+    n++;
+
+  } while (u >= BIZ_EPSILON * sum);
+
+  return(sum);
+
+}
+
+void kaiser(float *window, const int N, const float alpha){
+
+    int n;
+    const float M = N - 1;
+    float num;
+
+    for (n = 0; n < N; n++) {
+
+        num = besselI0(alpha * sqrtf(1.0 - powf((2.0 * n / M - 1), 2)));
+        window[n] = num / besselI0(alpha);
+        
+    }
+}
+
+void blackman_harris(float *window, const int N){
+
+    int n;
+    const float M = N - 1,
+          a0 = 0.35875,
+          a1 = 0.48829,
+          a2 = 0.14128,
+          a3 = 0.01168;
+    float term1 = 0.f,
+          term2 = 0.f,
+          term3 = 0.f;
+
+    for (n = 0; n < N; n++) {
+
+        term1 = a1 * cosf(2.0 * PI * n / M);
+        term2 = a2 * cosf(4.0 * PI * n / M);
+        term3 = a3 * cosf(6.0 * PI * n / M);
+
+        window[n] = a0 - term1 + term2 - term3;
+    }
+}