Fix a bug in the spectral density clipping

lib/spek-fft.c

@@ -22,12 +22,11 @@
 
 #include "spek-fft.h"
 
-struct spek_fft_plan * spek_fft_plan_new(int n, int threshold)
+struct spek_fft_plan * spek_fft_plan_new(int n)
 {
     struct spek_fft_plan *p = malloc(sizeof(struct spek_fft_plan));
     p->input = av_mallocz(sizeof(float) * n);
     p->output = av_mallocz(sizeof(float) * (n / 2 + 1));
-    p->threshold = threshold;
     int bits = 0;
     while (n) {
         n >>= 1;
@@ -51,8 +50,7 @@ void spek_fft_execute(struct spek_fft_plan *p)
             p->input[i * 2] * p->input[i * 2] +
             p->input[i * 2 + 1] * p->input[i * 2 + 1];
         val /= n * n;
-        val = 10.0 * log10f (val);
-        p->output[i] = val < p->threshold ? p->threshold : val;
+        p->output[i] = 10.0 * log10f (val);
     }
 }
 

lib/spek-fft.h

@@ -26,7 +26,6 @@ struct spek_fft_plan
     // Internal data.
     struct RDFTContext *cx;
     int n;
-    int threshold;
 
     // Exposed properties.
     float *input;
@@ -34,7 +33,7 @@ struct spek_fft_plan
 };
 
 // Allocate buffers and create a new FFT plan.
-struct spek_fft_plan * spek_fft_plan_new(int n, int threshold);
+struct spek_fft_plan * spek_fft_plan_new(int n);
 
 // Execute the FFT on plan->input.
 void spek_fft_execute(struct spek_fft_plan *p);

lib/spek-pipeline.c

@@ -45,7 +45,6 @@ struct spek_pipeline
     const struct spek_audio_properties *properties;
     int bands;
     int samples;
-    int threshold;
     spek_pipeline_cb cb;
     void *cb_data;
 
@@ -80,14 +79,13 @@ static void reader_sync(struct spek_pipeline *p, int pos);
 static float average_input(const struct spek_pipeline *p, void *buffer);
 
 struct spek_pipeline * spek_pipeline_open(
-    const char *path, int bands, int samples, int threshold, spek_pipeline_cb cb, void *cb_data)
+    const char *path, int bands, int samples, spek_pipeline_cb cb, void *cb_data)
 {
     struct spek_pipeline *p = malloc(sizeof(struct spek_pipeline));
     p->cx = spek_audio_open(path);
     p->properties = spek_audio_get_properties(p->cx);
     p->bands = bands;
     p->samples = samples;
-    p->threshold = threshold;
     p->cb = cb;
     p->cb_data = cb_data;
 
@@ -109,7 +107,7 @@ struct spek_pipeline * spek_pipeline_open(
         for (int i = 0; i < p->nfft; ++i) {
             p->coss[i] = cosf(cf * i);
         }
-        p->fft = spek_fft_plan_new(p->nfft, threshold);
+        p->fft = spek_fft_plan_new(p->nfft);
         p->input_size = p->nfft * (NFFT * 2 + 1);
         p->input = malloc(p->input_size * sizeof(float));
         p->output = malloc(bands * sizeof(float));

lib/spek-pipeline.h

@@ -25,7 +25,7 @@ struct spek_audio_properties;
 typedef void (*spek_pipeline_cb)(int sample, float *values, void *cb_data);
 
 struct spek_pipeline * spek_pipeline_open(
-    const char *path, int bands, int samples, int threshold, spek_pipeline_cb cb, void *cb_data);
+    const char *path, int bands, int samples, spek_pipeline_cb cb, void *cb_data);
 
 const struct spek_audio_properties * spek_pipeline_properties(struct spek_pipeline *pipeline);
 

src/spek-spectrogram.cc

@@ -17,6 +17,8 @@
  */
 
 #include <cmath>
+#include <sys/param.h>
+
 #include <wx/dcbuffer.h>
 
 extern "C" {
@@ -143,7 +145,6 @@ void SpekSpectrogram::on_size(wxSizeEvent& evt)
 
 void SpekSpectrogram::on_have_sample(SpekHaveSampleEvent& event)
 {
-    static double log10_threshold = log10(-THRESHOLD);
     int bands = event.get_bands();
     int sample = event.get_sample();
     const float *values = event.get_values();
@@ -154,9 +155,10 @@ void SpekSpectrogram::on_have_sample(SpekHaveSampleEvent& event)
     }
 
     // TODO: check image size, quit if wrong.
+    double range = log(1.0 - THRESHOLD);
     for (int y = 0; y < bands; y++) {
-        double level = log10(1.0 - THRESHOLD + values[y]) / log10_threshold;
-        if (level > 1.0) level = 1.0;
+        double value = MAX(THRESHOLD, values[y]);
+        double level = log(1.0 - THRESHOLD + value) / range;
         uint32_t color = spek_palette_spectrum(level);
         this->image.SetRGB(
             sample,
@@ -353,7 +355,6 @@ void SpekSpectrogram::start()
             this->path.utf8_str(),
             BANDS,
             samples,
-            THRESHOLD,
             pipeline_cb,
             this
         );