From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Sun, 15 Mar 2015 22:39:10 +0000 (+0100)
Subject: When training, use much faster interpolation.
X-Git-Url: https://git.sesse.net/?p=c64tapwav;a=commitdiff_plain;h=86fc2fc6160ce3331fe647ba5b436642f3819b4f

When training, use much faster interpolation.
---

diff --git a/decode.cpp b/decode.cpp
index 3662566..a832363 100644
--- a/decode.cpp
+++ b/decode.cpp
@@ -67,20 +67,27 @@ static float auto_level_freq = 200.0;
 static float min_level = 0.05f;
 
 // search for the value <limit> between [x,x+1]
+template<bool fast>
 double find_crossing(const std::vector<float> &pcm, int x, float limit)
 {
-	double upper = x;
-	double lower = x + 1;
-	while (lower - upper > 1e-3) {
-		double mid = 0.5f * (upper + lower);
-		if (lanczos_interpolate(pcm, mid) > limit) {
-			upper = mid;
-		} else {
-			lower = mid;
+	if (fast) {
+		// Do simple linear interpolation.
+		return x + (limit - pcm[x]) / (pcm[x + 1] - pcm[x]);
+	} else {
+		// Binary search for the zero crossing as given by Lanczos interpolation.
+		double upper = x;
+		double lower = x + 1;
+		while (lower - upper > 1e-3) {
+			double mid = 0.5f * (upper + lower);
+			if (lanczos_interpolate(pcm, mid) > limit) {
+				upper = mid;
+			} else {
+				lower = mid;
+			}
 		}
-	}
 
-	return 0.5f * (upper + lower);
+		return 0.5f * (upper + lower);
+	}
 }
 
 struct pulse {
@@ -396,6 +403,7 @@ std::vector<float> do_rc_filter(const std::vector<float>& pcm, float freq, int s
 	return filtered_pcm;
 }
 
+template<bool fast>
 std::vector<pulse> detect_pulses(const std::vector<float> &pcm, float hysteresis_upper_limit, float hysteresis_lower_limit, int sample_rate)
 {
 	std::vector<pulse> pulses;
@@ -409,7 +417,7 @@ std::vector<pulse> detect_pulses(const std::vector<float> &pcm, float hysteresis
 		} else if (pcm[i] < hysteresis_lower_limit) {
 			if (state == ABOVE) {
 				// down-flank!
-				double t = find_crossing(pcm, i - 1, hysteresis_lower_limit) * (1.0 / sample_rate) + crop_start;
+				double t = find_crossing<fast>(pcm, i - 1, hysteresis_lower_limit) * (1.0 / sample_rate) + crop_start;
 				if (last_downflank > 0) {
 					pulse p;
 					p.time = t;
@@ -526,8 +534,8 @@ void spsa_train(const std::vector<float> &pcm, int sample_rate)
 			vals2[i] = std::max(std::min(vals[i] + c * p[i], 1.0f), -1.0f);
 		}
 
-		std::vector<pulse> pulses1 = detect_pulses(do_fir_filter(pcm, vals1 + 2), vals1[0], vals1[1], sample_rate);
-		std::vector<pulse> pulses2 = detect_pulses(do_fir_filter(pcm, vals2 + 2), vals2[0], vals2[1], sample_rate);
+		std::vector<pulse> pulses1 = detect_pulses<true>(do_fir_filter(pcm, vals1 + 2), vals1[0], vals1[1], sample_rate);
+		std::vector<pulse> pulses2 = detect_pulses<true>(do_fir_filter(pcm, vals2 + 2), vals2[0], vals2[1], sample_rate);
 		float badness1 = eval_badness(pulses1, 1.0);
 		float badness2 = eval_badness(pulses2, 1.0);
 
@@ -611,7 +619,7 @@ int main(int argc, char **argv)
 		exit(0);
 	}
 
-	std::vector<pulse> pulses = detect_pulses(pcm, hysteresis_upper_limit, hysteresis_lower_limit, sample_rate);
+	std::vector<pulse> pulses = detect_pulses<false>(pcm, hysteresis_upper_limit, hysteresis_lower_limit, sample_rate);
 
 	double calibration_factor = 1.0;
 	if (do_calibrate) {