From ba5738446c246487bf73f1914b4fa37bbb41f752 Mon Sep 17 00:00:00 2001
From: Paul Licameli <paul.licameli@gmail.com>
Date: Wed, 3 Jun 2015 13:11:17 -0400
Subject: [PATCH] Bug1009: Correct interaction of Zero Padding and Frequency
 Gain...

... also an excuse to pull out a function I will want to reuse in a later
project.  The real fix was simply to use fftLen not windowSize.
---
 src/WaveClip.cpp | 45 +++++++++++++++++++++++++++------------------
 src/WaveClip.h   |  7 +++++++
 2 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/src/WaveClip.cpp b/src/WaveClip.cpp
index c42e75ba5..94be7305d 100644
--- a/src/WaveClip.cpp
+++ b/src/WaveClip.cpp
@@ -842,6 +842,25 @@ void RecreateWindow(
 }
 }
 
+void WaveClip::ComputeSpectrogramGainFactors(int fftLen, int frequencyGain, std::vector<float> &gainFactors)
+{
+   if (frequencyGain > 0) {
+      // Compute a frequency-dependent gain factor
+      // scaled such that 1000 Hz gets a gain of 0dB
+
+      // This is the reciprocal of the bin number of 1000 Hz:
+      const double factor = ((double)mRate / (double)fftLen) / 1000.0;
+
+      const int half = fftLen / 2;
+      gainFactors.reserve(half);
+      // Don't take logarithm of zero!  Let bin 0 replicate the gain factor for bin 1.
+      gainFactors.push_back(frequencyGain*log10(factor));
+      for (sampleCount x = 1; x < half; x++) {
+         gainFactors.push_back(frequencyGain*log10(factor * x));
+      }
+   }
+}
+
 bool WaveClip::GetSpectrogram(WaveTrackCache &waveTrackCache,
                               float *freq, sampleCount *where,
                               int numPixels,
@@ -852,7 +871,7 @@ bool WaveClip::GetSpectrogram(WaveTrackCache &waveTrackCache,
    int maxFreq = gPrefs->Read(wxT("/Spectrum/MaxFreq"), 8000L);
    int range = gPrefs->Read(wxT("/Spectrum/Range"), 80L);
    int gain = gPrefs->Read(wxT("/Spectrum/Gain"), 20L);
-   int frequencygain = gPrefs->Read(wxT("/Spectrum/FrequencyGain"), 0L);
+   int frequencyGain = gPrefs->Read(wxT("/Spectrum/FrequencyGain"), 0L);
    int windowType;
    int windowSize = gPrefs->Read(wxT("/Spectrum/FFTSize"), 256);
 #ifdef EXPERIMENTAL_FFT_SKIP_POINTS
@@ -897,7 +916,7 @@ bool WaveClip::GetSpectrogram(WaveTrackCache &waveTrackCache,
       mSpecCache->windowTypeOld == windowType &&
       mSpecCache->windowSizeOld == windowSize &&
       mSpecCache->zeroPaddingFactorOld == zeroPaddingFactor &&
-      mSpecCache->frequencyGainOld == frequencygain &&
+      mSpecCache->frequencyGainOld == frequencyGain &&
 #ifdef EXPERIMENTAL_FFT_SKIP_POINTS
       mSpecCache->fftSkipPointsOld == fftSkipPoints &&
 #endif //EXPERIMENTAL_FFT_SKIP_POINTS
@@ -986,18 +1005,10 @@ bool WaveClip::GetSpectrogram(WaveTrackCache &waveTrackCache,
    mSpecCache->windowTypeOld = windowType;
    mSpecCache->windowSizeOld = windowSize;
    mSpecCache->zeroPaddingFactorOld = zeroPaddingFactor;
-   mSpecCache->frequencyGainOld = frequencygain;
+   mSpecCache->frequencyGainOld = frequencyGain;
 
-   float *gainfactor = NULL;
-   if(frequencygain > 0) {
-      // Compute a frequency-dependant gain factor
-      // scaled such that 1000 Hz gets a gain of 0dB
-      double factor = 0.001*(double)mRate/(double)windowSize;
-      gainfactor = new float[half];
-      for(sampleCount x = 0; x < half; x++) {
-         gainfactor[x] = frequencygain*log10(factor * x);
-      }
-   }
+   std::vector<float> gainFactors;
+   ComputeSpectrogramGainFactors(fftLen, frequencyGain, gainFactors);
 
    for (sampleCount x = 0; x < mSpecCache->len; x++)
       if (recalc[x]) {
@@ -1080,16 +1091,14 @@ bool WaveClip::GetSpectrogram(WaveTrackCache &waveTrackCache,
                            mRate, &mSpecCache->freq[half * x],
                            autocorrelation, windowType);
 #endif // EXPERIMENTAL_USE_REALFFTF
-           if(gainfactor) {
-              // Apply a frequency-dependant gain factor
+           if (!gainFactors.empty()) {
+              // Apply a frequency-dependent gain factor
               for(i=0; i<half; i++)
-                 mSpecCache->freq[half * x + i] += gainfactor[i];
+                 mSpecCache->freq[half * x + i] += gainFactors[i];
            }
          }
       }
 
-   if(gainfactor)
-      delete[] gainfactor;
    delete[]buffer;
    delete[]recalc;
    delete oldCache;
diff --git a/src/WaveClip.h b/src/WaveClip.h
index 3c2de5d85..86eeaec07 100644
--- a/src/WaveClip.h
+++ b/src/WaveClip.h
@@ -29,6 +29,8 @@
 #include <wx/list.h>
 #include <wx/msgdlg.h>
 
+#include <vector>
+
 class Envelope;
 class WaveCache;
 class WaveTrackCache;
@@ -187,6 +189,11 @@ public:
     * calculations and Contrast */
    bool GetWaveDisplay(WaveDisplay &display,
                        double t0, double pixelsPerSecond, bool &isLoadingOD);
+   void ComputeSpectrogramGainFactors(
+         int fftLen,
+         int frequencyGain, // db/decade
+         std::vector<float> &gainFactors
+      );
    bool GetSpectrogram(WaveTrackCache &cache,
                        float *buffer, sampleCount *where,
                        int numPixels,