From: sgunderson@bigfoot.com <>
Date: Mon, 19 Jul 2010 23:42:44 +0000 (+0200)
Subject: In glpitch, stretch the x axis a bit so that we have more precision around the intere... 
X-Git-Url: https://git.sesse.net/?p=pitch;a=commitdiff_plain;h=8603ad0d114005cee0dab2f7facd4faebae57f5d

In glpitch, stretch the x axis a bit so that we have more precision around the interesting parts.
---

diff --git a/config.h b/config.h
index 87f25e9..da6a691 100644
--- a/config.h
+++ b/config.h
@@ -15,4 +15,12 @@
 
 #define TUNING WELL_TEMPERED_GUITAR
 
+// Compress the x scale of the glpitch display in a nonlinear way
+// so that the view is more precise around the reference frequencies.
+#define COMPRESS_PITCH_DISPLAY 1
+
+// Lower is more compressed. Anything over 2-3 is probably going to negate
+// the entire effect.
+#define PITCH_COMPRESSION_SIGMA 1.0
+
 #endif /* !defined(_CONFIG_H) */
diff --git a/glpitch.cpp b/glpitch.cpp
index a3c3010..4aea821 100644
--- a/glpitch.cpp
+++ b/glpitch.cpp
@@ -9,11 +9,46 @@
 #define MIN_X -40
 #define MAX_X 5
 
-double find_pos(double freq)
+double find_linear_pos(double freq)
 {
 	return 12.0 * log2(freq / BASE_PITCH) - 3.0;
 }
 
+#if COMPRESS_PITCH_DISPLAY
+// bend the scale a bit to get more precision around the interesting points
+double magnifying_glass(double x)
+{
+	double sigma = PITCH_COMPRESSION_SIGMA;
+	double div = 1.0 / sqrt(2.0 * sigma * sigma);
+	return
+		erf((x - find_linear_pos(notes[0].freq)) * div) +
+		erf((x - find_linear_pos(notes[1].freq)) * div) +
+		erf((x - find_linear_pos(notes[2].freq)) * div) +
+		erf((x - find_linear_pos(notes[3].freq)) * div) +
+		erf((x - find_linear_pos(notes[4].freq)) * div) +
+		erf((x - find_linear_pos(notes[5].freq)) * div);
+}
+
+// like nonlinear_func, but f(MIN_X) = MIN_X and f(MAX_X) = MAX_X
+double normalized_magnifying_glass(double x)
+{
+	double y = magnifying_glass(x);
+	double min_y = magnifying_glass(MIN_X);
+	double max_y = magnifying_glass(MAX_X);
+	return (y - min_y) * (MAX_X - MIN_X) / (max_y - min_y) + MIN_X;
+}
+#endif /* COMPRESS_PITCH_DISPLAY */
+
+double find_display_pos(double freq)
+{
+	double linear_pos = find_linear_pos(freq);
+#if COMPRESS_PITCH_DISPLAY
+	return normalized_magnifying_glass(linear_pos);
+#else
+	return linear_pos;
+#endif
+}
+
 int main(void)
 {
 	PitchDetector pd(SAMPLE_RATE, FFT_LENGTH, PAD_FACTOR, OVERLAP);
@@ -63,7 +98,7 @@ int main(void)
 		glEnd();
 
 		if (peak.second - log10(FFT_LENGTH) >= 0.0) {
-			double peak_pos = find_pos(peak.first);
+			double peak_pos = find_display_pos(peak.first);
 
 			glBlendFunc(GL_SRC_ALPHA, GL_ONE);
 			glBegin(GL_QUADS);	
@@ -79,7 +114,7 @@ int main(void)
 		glBegin(GL_LINES);
 
 		for (int i = 0; i < 6; ++i) {
-			double pos = find_pos(notes[i].freq);
+			double pos = find_display_pos(notes[i].freq);
 			glVertex2f(pos, 0.0f);
 			glVertex2f(pos, 1.0f);
 		}