porting the dithering function from kaldi

kaldi-native-fbank/csrc/feature-window.cc

@@ -5,16 +5,13 @@
 // This file is copied/modified from kaldi/src/feat/feature-window.cc
 
 #include "kaldi-native-fbank/csrc/feature-window.h"
+#include "kaldi-native-fbank/csrc/kaldi-math.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 #include <vector>
 
-#ifndef M_2PI
-#define M_2PI 6.283185307179586476925286766559005
-#endif
-
 namespace knf {
 
 std::ostream &operator<<(std::ostream &os, const FrameExtractionOptions &opts) {
@@ -205,6 +202,14 @@ float InnerProduct(const float *a, const float *b, int32_t n) {
   return sum;
 }
 
+void Dither(float *d, int32_t n, float dither_value) {
+  if (dither_value == 0.0)
+    return;
+  RandomState rstate;
+  for (int32_t i = 0; i < n; i++)
+    d[i] += RandGauss(&rstate) * dither_value;
+}
+
 static void Preemphasize(float *d, int32_t n, float preemph_coeff) {
   if (preemph_coeff == 0.0) {
     return;
@@ -223,6 +228,9 @@ void ProcessWindow(const FrameExtractionOptions &opts,
                    float *log_energy_pre_window /*= nullptr*/) {
   int32_t frame_length = opts.WindowSize();
 
+  if (opts.dither != 0.0)
+    Dither(window, frame_length, opts.dither);
+
   if (opts.remove_dc_offset) {
     RemoveDcOffset(window, frame_length);
   }

kaldi-native-fbank/csrc/kaldi-math.h

@@ -0,0 +1,43 @@
+// kaldi-native-fbank/csrc/feature-window.h
+//
+// Copyright (c)  2022  Xiaomi Corporation (authors: Fangjun Kuang)
+
+// This file is copied/modified from kaldi/src/feat/feature-window.h
+
+#pragma once
+
+#include <cmath>  // logf, sqrtf, cosf
+#include <cstdlib>  // RAND_MAX
+
+#ifndef M_PI
+#define M_PI 3.1415926535897932384626433832795
+#endif
+
+#ifndef M_2PI
+#define M_2PI 6.283185307179586476925286766559005
+#endif
+
+namespace knf {
+
+inline float Log(float x) { return logf(x); }
+
+// Returns a random integer between 0 and RAND_MAX, inclusive
+int Rand(struct RandomState* state = NULL);
+
+// State for thread-safe random number generator
+struct RandomState {
+  RandomState();
+  unsigned seed;
+};
+
+/// Returns a random number strictly between 0 and 1.
+inline float RandUniform(struct RandomState* state = NULL) {
+  return static_cast<float>((Rand(state) + 1.0) / (RAND_MAX+2.0));
+}
+
+inline float RandGauss(struct RandomState* state = NULL) {
+  return static_cast<float>(sqrtf (-2 * Log(RandUniform(state)))
+                            * cosf(2*M_PI*RandUniform(state)));
+}
+
+}  // namespace knf