Clean up interpolation a bit.

[c64tapwav] / decode.cpp

diff --git a/decode.cpp b/decode.cpp
index 8e0adaa7059ea3dc7e78ecd153d48b78c09546b3..ca0c675e411fbddfca3037cddbbd7fc1e69083e7 100644 (file)
--- a/decode.cpp
+++ b/decode.cpp
@@ -6,7 +6,8 @@
 #include <vector>
 #include <algorithm>
 
-#define LANCZOS_RADIUS 30
+#include "interpolate.h"
+
 #define BUFSIZE 4096
 #define HYSTERESIS_LIMIT 3000
 #define SAMPLE_RATE 44100
@@ -15,7 +16,7 @@
 
 #define SYNC_PULSE_START 1000
 #define SYNC_PULSE_END 15000
-#define SYNC_PULSE_LENGTH 380.0
+#define SYNC_PULSE_LENGTH 378.0
 #define SYNC_TEST_TOLERANCE 1.10
 
 struct tap_header {
@@ -25,45 +26,6 @@ struct tap_header {
        unsigned int data_len;
 };
 
-double sinc(double x)
-{
-       if (fabs(x) < 1e-6) {
-               return 1.0f - fabs(x);
-       } else {
-               return sin(x) / x;
-       }
-}
-
-#if 0
-double weight(double x)
-{
-       if (fabs(x) > LANCZOS_RADIUS) {
-               return 0.0f;
-       }
-       return sinc(M_PI * x) * sinc(M_PI * x / LANCZOS_RADIUS);
-}
-#else
-double weight(double x)
-{
-       if (fabs(x) > 1.0f) {
-               return 0.0f;
-       }
-       return 1.0f - fabs(x);
-}
-#endif
-
-double interpolate(const std::vector<short> &pcm, double i)
-{
-       int lower = std::max<int>(ceil(i - LANCZOS_RADIUS), 0);
-       int upper = std::min<int>(floor(i + LANCZOS_RADIUS), pcm.size() - 1);
-       double sum = 0.0f;
-
-       for (int x = lower; x <= upper; ++x) {
-               sum += pcm[x] * weight(i - x);
-       }
-       return sum;
-}
-       
 // between [x,x+1]
 double find_zerocrossing(const std::vector<short> &pcm, int x)
 {
@@ -81,7 +43,7 @@ double find_zerocrossing(const std::vector<short> &pcm, int x)
        double upper = x + 1;
        while (upper - lower > 1e-6) {
                double mid = 0.5f * (upper + lower);
-               if (interpolate(pcm, mid) > 0) {
+               if (lanczos_interpolate(pcm, mid) > 0) {
                        upper = mid;
                } else {
                        lower = mid;
@@ -125,10 +87,31 @@ int main(int argc, char **argv)
        // Find the flanks.
        int last_bit = -1;
        double last_upflank = -1;
-       int last_max_level = 0;
        for (unsigned i = 0; i < pcm.size(); ++i) {
                int bit = (pcm[i] > 0) ? 1 : 0;
-               if (bit == 1 && last_bit == 0 && last_max_level > HYSTERESIS_LIMIT) {
+               if (bit == 1 && last_bit == 0) {
+                       // Check if we ever go up above HYSTERESIS_LIMIT before we dip down again.
+                       bool true_pulse = false;
+                       unsigned j;
+                       int max_level_after = -32768;
+                       for (j = i; j < pcm.size(); ++j) {
+                               max_level_after = std::max<int>(max_level_after, pcm[j]);
+                               if (pcm[j] < 0) break;
+                               if (pcm[j] > HYSTERESIS_LIMIT) {
+                                       true_pulse = true;
+                                       break;
+                               }
+                       }
+
+                       if (!true_pulse) {
+#if 0
+                               fprintf(stderr, "Ignored up-flank at %.6f seconds due to hysteresis (%d < %d).\n",
+                                       double(i) / SAMPLE_RATE, max_level_after, HYSTERESIS_LIMIT);
+#endif
+                               i = j;
+                               continue;
+                       } 
+
                        // up-flank!
                        double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
                        if (last_upflank > 0) {
@@ -138,9 +121,7 @@ int main(int argc, char **argv)
                                pulses.push_back(p);
                        }
                        last_upflank = t;
-                       last_max_level = 0;
                }
-               last_max_level = std::max(last_max_level, abs(pcm[i]));
                last_bit = bit;
        }
 
@@ -155,8 +136,8 @@ int main(int argc, char **argv)
                }
                double mean_length = C64_FREQUENCY * sum / (SYNC_PULSE_END - SYNC_PULSE_START);
                calibration_factor = SYNC_PULSE_LENGTH / mean_length;
-               fprintf(stderr, "Calibrated sync pulse length: %.2f -> 380.0 (change %+.2f%%)\n",
-                       mean_length, 100.0 * (calibration_factor - 1.0));
+               fprintf(stderr, "Calibrated sync pulse length: %.2f -> %.2f (change %+.2f%%)\n",
+                       mean_length, SYNC_PULSE_LENGTH, 100.0 * (calibration_factor - 1.0));
 
                // Check for pulses outside +/- 10% (sign of misdetection).
                for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {