Change the window function

And add Blackman-Harris in addition to Hann and Hamming.

References alexkay#94.

MANUAL.md

@@ -53,6 +53,9 @@ On OS X use the Command key instead of Ctrl.
 `Ctrl-Shift-up`, `Ctrl-Shift-down`
 :   Change the upper limit of the dynamic range in dBFS.
 
+`f`, `F`
+:   Change the DFT window function.
+
 `s`, `S`
 :   Change the DFT window size.
 

src/spek-pipeline.cc

@@ -25,6 +25,7 @@ struct spek_pipeline
 {
     std::unique_ptr<AudioFile> file;
     std::unique_ptr<FFTPlan> fft;
+    enum window_function window_function;
     int samples;
     spek_pipeline_cb cb;
     void *cb_data;
@@ -60,6 +61,7 @@ static void reader_sync(struct spek_pipeline *p, int pos);
 struct spek_pipeline * spek_pipeline_open(
     std::unique_ptr<AudioFile> file,
     std::unique_ptr<FFTPlan> fft,
+    enum window_function window_function,
     int samples,
     spek_pipeline_cb cb,
     void *cb_data
@@ -68,6 +70,7 @@ struct spek_pipeline * spek_pipeline_open(
     spek_pipeline *p = new spek_pipeline();
     p->file = std::move(file);
     p->fft = std::move(fft);
+    p->window_function = window_function;
     p->samples = samples;
     p->cb = cb;
     p->cb_data = cb_data;
@@ -319,6 +322,19 @@ static void reader_sync(struct spek_pipeline *p, int pos)
     pthread_mutex_unlock(&p->worker_mutex);
 }
 
+static float get_window(enum window_function f, int i, float *coss, int n) {
+    switch (f) {
+    case WINDOW_HANN:
+        return 0.5f * (1.0f - coss[i]);
+    case WINDOW_HAMMING:
+        return 0.53836f - 0.46164f * coss[i];
+    case WINDOW_BLACKMAN_HARRIS:
+        return 0.35875f - 0.48829f * coss[i] + 0.14128f * coss[2*i % n] - 0.01168f * coss[3*i % n];
+    default:
+        assert(false);
+    }
+}
+
 static void * worker_func(void *pp)
 {
     struct spek_pipeline *p = (spek_pipeline*)pp;
@@ -370,11 +386,7 @@ static void * worker_func(void *pp)
                 prev_head = head;
                 for (int i = 0; i < p->nfft; i++) {
                     float val = p->input[(p->input_size + head - p->nfft + i) % p->input_size];
-                    // TODO: allow the user to chose the window function
-                    // Hamming window.
-                    // val *= 0.53836f - 0.46164f * coss[i];
-                    // Hann window.
-                    val *= 0.5f * (1.0f - p->coss[i]);
+                    val *= get_window(p->window_function, i, p->coss, p->nfft);
                     p->fft->set_input(i, val);
                 }
                 p->fft->execute();

src/spek-pipeline.h

@@ -7,11 +7,20 @@ class AudioFile;
 class FFTPlan;
 struct spek_pipeline;
 
+enum window_function {
+    WINDOW_HANN,
+    WINDOW_HAMMING,
+    WINDOW_BLACKMAN_HARRIS,
+    WINDOW_COUNT,
+    WINDOW_DEFAULT = WINDOW_HANN,
+};
+
 typedef void (*spek_pipeline_cb)(int bands, int sample, float *values, void *cb_data);
 
 struct spek_pipeline * spek_pipeline_open(
     std::unique_ptr<AudioFile> file,
     std::unique_ptr<FFTPlan> fft,
+    enum window_function window_function,
     int samples,
     spek_pipeline_cb cb,
     void *cb_data

src/spek-spectrogram.cc

@@ -5,7 +5,6 @@
 #include "spek-audio.h"
 #include "spek-events.h"
 #include "spek-fft.h"
-#include "spek-pipeline.h"
 #include "spek-platform.h"
 #include "spek-ruler.h"
 #include "spek-utils.h"
@@ -48,6 +47,7 @@ SpekSpectrogram::SpekSpectrogram(wxFrame *parent) :
     audio(new Audio()), // TODO: refactor
     fft(new FFT()),
     pipeline(NULL),
+    window_function(WINDOW_DEFAULT),
     duration(0.0),
     sample_rate(0),
     palette(PALETTE_DEFAULT),
@@ -102,6 +102,11 @@ void SpekSpectrogram::on_char(wxKeyEvent& evt)
         this->urange = spek_min(this->urange + 1, MAX_RANGE);
     } else if (CS && D) {
         this->urange = spek_max(this->urange - 1, this->lrange + 1);
+    } else if (S && evt.GetKeyCode() == 'F') {
+        this->window_function = (enum window_function) ((this->window_function + 1) % WINDOW_COUNT);
+    } else if (N && evt.GetKeyCode() == 'f') {
+        this->window_function =
+            (enum window_function) ((this->window_function - 1 + WINDOW_COUNT) % WINDOW_COUNT);
     } else if (S && evt.GetKeyCode() == 'S') {
         this->fft_bits = spek_min(this->fft_bits + 1, MAX_FFT_BITS);
         this->create_palette();
@@ -358,6 +363,7 @@ void SpekSpectrogram::start()
         this->pipeline = spek_pipeline_open(
             this->audio->open(std::string(this->path.utf8_str())),
             this->fft->create(this->fft_bits),
+            this->window_function,
             samples,
             pipeline_cb,
             this

src/spek-spectrogram.h

@@ -5,6 +5,7 @@
 #include <wx/wx.h>
 
 #include "spek-palette.h"
+#include "spek-pipeline.h"
 
 class Audio;
 class FFT;
@@ -34,6 +35,7 @@ class SpekSpectrogram : public wxWindow
     std::unique_ptr<Audio> audio;
     std::unique_ptr<FFT> fft;
     spek_pipeline *pipeline;
+    enum window_function window_function;
     wxString path;
     wxString desc;
     double duration;