Change hysteresis so that it is a bit more like a traditional Schmitt trigger; the...

[c64tapwav] / decode.cpp

diff --git a/decode.cpp b/decode.cpp
index f645588923bcb079f6f30b52f505f07535ab71f8..4c5da355d2255b5565e788f2bf58716c2a81ff8e 100644 (file)
--- a/decode.cpp
+++ b/decode.cpp
@@ -32,7 +32,8 @@
 #define GAMMA 0.166
 #define ALPHA 1.0
 
-static float hysteresis_limit = 3000.0 / 32768.0;
+static float hysteresis_upper_limit = 3000.0 / 32768.0;
+static float hysteresis_lower_limit = -3000.0 / 32768.0;
 static bool do_calibrate = true;
 static bool output_cycles_plot = false;
 static bool do_crop = false;
@@ -56,24 +57,14 @@ static bool do_train = false;
 // possibly caused misdetected pulses in these segments.
 static float min_level = 0.05f;
 
-// between [x,x+1]
-double find_zerocrossing(const std::vector<float> &pcm, int x)
+// search for the value <limit> between [x,x+1]
+double find_crossing(const std::vector<float> &pcm, int x, float limit)
 {
-       if (pcm[x] == 0) {
-               return x;
-       }
-       if (pcm[x + 1] == 0) {
-               return x + 1;
-       }
-
-       assert(pcm[x + 1] < 0);
-       assert(pcm[x] > 0);
-
        double upper = x;
        double lower = x + 1;
        while (lower - upper > 1e-3) {
                double mid = 0.5f * (upper + lower);
-               if (lanczos_interpolate(pcm, mid) > 0) {
+               if (lanczos_interpolate(pcm, mid) > limit) {
                        upper = mid;
                } else {
                        lower = mid;
@@ -241,9 +232,17 @@ void parse_options(int argc, char **argv)
                        output_cycles_plot = true;
                        break;
 
-               case 'l':
-                       hysteresis_limit = atof(optarg) / 32768.0;
+               case 'l': {
+                       const char *hyststr = strtok(optarg, ": ");
+                       hysteresis_upper_limit = atof(hyststr) / 32768.0;
+                       hyststr = strtok(NULL, ": ");
+                       if (hyststr == NULL) {
+                               hysteresis_lower_limit = -hysteresis_upper_limit;
+                       } else {
+                               hysteresis_lower_limit = atof(hyststr) / 32768.0;
+                       }
                        break;
+               }
 
                case 'f': {
                        const char *coeffstr = strtok(optarg, ": ");
@@ -373,44 +372,25 @@ std::vector<pulse> detect_pulses(const std::vector<float> &pcm, int sample_rate)
        std::vector<pulse> pulses;
 
        // Find the flanks.
-       int last_bit = -1;
+       enum State { START, ABOVE, BELOW } state = START;
        double last_downflank = -1;
        for (unsigned i = 0; i < pcm.size(); ++i) {
-               int bit = (pcm[i] > 0) ? 1 : 0;
-               if (bit == 0 && last_bit == 1) {
-                       // Check if we ever go up above <hysteresis_limit> before we dip down again.
-                       bool true_pulse = false;
-                       unsigned j;
-                       int min_level_after = 32767;
-                       for (j = i; j < pcm.size(); ++j) {
-                               min_level_after = std::min<int>(min_level_after, pcm[j]);
-                               if (pcm[j] > 0) break;
-                               if (pcm[j] < -hysteresis_limit) {
-                                       true_pulse = true;
-                                       break;
+               if (pcm[i] > hysteresis_upper_limit) {
+                       state = ABOVE;
+               } 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;
+                               if (last_downflank > 0) {
+                                       pulse p;
+                                       p.time = t;
+                                       p.len = t - last_downflank;
+                                       pulses.push_back(p);
                                }
+                               last_downflank = t;
                        }
-
-                       if (!true_pulse) {
-#if 0
-                               fprintf(stderr, "Ignored down-flank at %.6f seconds due to hysteresis (%d < %d).\n",
-                                       double(i) / sample_rate, -min_level_after, hysteresis_limit);
-#endif
-                               i = j;
-                               continue;
-                       } 
-
-                       // down-flank!
-                       double t = find_zerocrossing(pcm, i - 1) * (1.0 / sample_rate) + crop_start;
-                       if (last_downflank > 0) {
-                               pulse p;
-                               p.time = t;
-                               p.len = t - last_downflank;
-                               pulses.push_back(p);
-                       }
-                       last_downflank = t;
+                       state = BELOW;
                }
-               last_bit = bit;
        }
        return pulses;
 }