git.sesse.net Git - c64tapwav/blob - decode.cpp

   1 #include <stdio.h>
   2 #include <string.h>
   3 #include <math.h>
   4 #include <assert.h>
   5 #include <limits.h>
   6 #include <getopt.h>
   7 #include <vector>
   8 #include <algorithm>
   9
  10 #include "audioreader.h"
  11 #include "interpolate.h"
  12 #include "tap.h"
  13
  14 #define BUFSIZE 4096
  15 #define C64_FREQUENCY 985248
  16 #define SYNC_PULSE_START 1000
  17 #define SYNC_PULSE_END 20000
  18 #define SYNC_PULSE_LENGTH 378.0
  19 #define SYNC_TEST_TOLERANCE 1.10
  20
  21 #define NUM_FILTER_COEFF 32
  22
  23 static float hysteresis_limit = 3000.0 / 32768.0;
  24 static bool do_calibrate = true;
  25 static bool output_cycles_plot = false;
  26 static bool use_filter = false;
  27 static bool do_crop = false;
  28 static float crop_start = 0.0f, crop_end = HUGE_VAL;
  29 static float filter_coeff[NUM_FILTER_COEFF] = { 1.0f };  // The rest is filled with 0.
  30 static bool output_filtered = false;
  31 static bool quiet = false;
  32
  33 // between [x,x+1]
  34 double find_zerocrossing(const std::vector<float> &pcm, int x)
  35 {
  36         if (pcm[x] == 0) {
  37                 return x;
  38         }
  39         if (pcm[x + 1] == 0) {
  40                 return x + 1;
  41         }
  42
  43         assert(pcm[x + 1] < 0);
  44         assert(pcm[x] > 0);
  45
  46         double upper = x;
  47         double lower = x + 1;
  48         while (lower - upper > 1e-3) {
  49                 double mid = 0.5f * (upper + lower);
  50                 if (lanczos_interpolate(pcm, mid) > 0) {
  51                         upper = mid;
  52                 } else {
  53                         lower = mid;
  54                 }
  55         }
  56
  57         return 0.5f * (upper + lower);
  58 }
  59
  60 struct pulse {
  61         double time;  // in seconds from start
  62         double len;   // in seconds
  63 };
  64
  65 // Calibrate on the first ~25k pulses (skip a few, just to be sure).
  66 double calibrate(const std::vector<pulse> &pulses) {
  67         if (pulses.size() < SYNC_PULSE_END) {
  68                 fprintf(stderr, "Too few pulses, not calibrating!\n");
  69                 return 1.0;
  70         }
  71
  72         int sync_pulse_end = -1;
  73         double sync_pulse_stddev = -1.0;
  74
  75         // Compute the standard deviation (to check for uneven speeds).
  76         // If it suddenly skyrockets, we assume that sync ended earlier
  77         // than we thought (it should be 25000 cycles), and that we should
  78         // calibrate on fewer cycles.
  79         for (int try_end : { 2000, 4000, 5000, 7500, 10000, 15000, SYNC_PULSE_END }) {
  80                 double sum2 = 0.0;
  81                 for (int i = SYNC_PULSE_START; i < try_end; ++i) {
  82                         double cycles = pulses[i].len * C64_FREQUENCY;
  83                         sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH);
  84                 }
  85                 double stddev = sqrt(sum2 / (try_end - SYNC_PULSE_START - 1));
  86                 if (sync_pulse_end != -1 && stddev > 5.0 && stddev / sync_pulse_stddev > 1.3) {
  87                         fprintf(stderr, "Stopping at %d sync pulses because standard deviation would be too big (%.2f cycles); shorter-than-usual trailer?\n",
  88                                 sync_pulse_end, stddev);
  89                         break;
  90                 }
  91                 sync_pulse_end = try_end;
  92                 sync_pulse_stddev = stddev;
  93         }
  94         if (!quiet) {
  95                 fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n",
  96                         sync_pulse_stddev);
  97         }
  98
  99         double sum = 0.0;
 100         for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) {
 101                 sum += pulses[i].len;
 102         }
 103         double mean_length = C64_FREQUENCY * sum / (sync_pulse_end - SYNC_PULSE_START);
 104         double calibration_factor = SYNC_PULSE_LENGTH / mean_length;
 105         if (!quiet) {
 106                 fprintf(stderr, "Calibrated sync pulse length: %.2f -> %.2f (change %+.2f%%)\n",
 107                         mean_length, SYNC_PULSE_LENGTH, 100.0 * (calibration_factor - 1.0));
 108         }
 109
 110         // Check for pulses outside +/- 10% (sign of misdetection).
 111         for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) {
 112                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 113                 if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
 114                         fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 115                                 pulses[i].time, cycles);
 116                 }
 117         }
 118
 119         return calibration_factor;
 120 }
 121
 122 void output_tap(const std::vector<pulse>& pulses, double calibration_factor)
 123 {
 124         std::vector<char> tap_data;
 125         for (unsigned i = 0; i < pulses.size(); ++i) {
 126                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 127                 int len = lrintf(cycles / TAP_RESOLUTION);
 128                 if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) {
 129                         fprintf(stderr, "Cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 130                                         pulses[i].time, cycles);
 131                 }
 132                 if (len <= 255) {
 133                         tap_data.push_back(len);
 134                 } else {
 135                         int overflow_len = lrintf(cycles);
 136                         tap_data.push_back(0);
 137                         tap_data.push_back(overflow_len & 0xff);
 138                         tap_data.push_back((overflow_len >> 8) & 0xff);
 139                         tap_data.push_back(overflow_len >> 16);
 140                 }
 141         }
 142
 143         tap_header hdr;
 144         memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
 145         hdr.version = 1;
 146         hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
 147         hdr.data_len = tap_data.size();
 148
 149         fwrite(&hdr, sizeof(hdr), 1, stdout);
 150         fwrite(tap_data.data(), tap_data.size(), 1, stdout);
 151 }
 152
 153 static struct option long_options[] = {
 154         {"no-calibrate",     0,                 0, 's' },
 155         {"plot-cycles",      0,                 0, 'p' },
 156         {"hysteresis-limit", required_argument, 0, 'l' },
 157         {"filter",           required_argument, 0, 'f' },
 158         {"output-filtered",  0,                 0, 'F' },
 159         {"crop",             required_argument, 0, 'c' },
 160         {"quiet",            0,                 0, 'q' },
 161         {"help",             0,                 0, 'h' },
 162         {0,                  0,                 0, 0   }
 163 };
 164
 165 void help()
 166 {
 167         fprintf(stderr, "decode [OPTIONS] AUDIO-FILE > TAP-FILE\n");
 168         fprintf(stderr, "\n");
 169         fprintf(stderr, "  -s, --no-calibrate           do not try to calibrate on sync pulse length\n");
 170         fprintf(stderr, "  -p, --plot-cycles            output debugging info to cycles.plot\n");
 171         fprintf(stderr, "  -l, --hysteresis-limit VAL   change amplitude threshold for ignoring pulses (0..32768)\n");
 172         fprintf(stderr, "  -f, --filter C1:C2:C3:...    specify FIR filter (up to %d coefficients)\n", NUM_FILTER_COEFF);
 173         fprintf(stderr, "  -F, --output-filtered        output filtered waveform to filtered.raw\n");
 174         fprintf(stderr, "  -c, --crop START[:END]       use only the given part of the file\n");
 175         fprintf(stderr, "  -q, --quiet                  suppress some informational messages\n");
 176         fprintf(stderr, "  -h, --help                   display this help, then exit\n");
 177         exit(1);
 178 }
 179
 180 void parse_options(int argc, char **argv)
 181 {
 182         for ( ;; ) {
 183                 int option_index = 0;
 184                 int c = getopt_long(argc, argv, "spl:f:Fc:qh", long_options, &option_index);
 185                 if (c == -1)
 186                         break;
 187
 188                 switch (c) {
 189                 case 's':
 190                         do_calibrate = false;
 191                         break;
 192
 193                 case 'p':
 194                         output_cycles_plot = true;
 195                         break;
 196
 197                 case 'l':
 198                         hysteresis_limit = atof(optarg) / 32768.0;
 199                         break;
 200
 201                 case 'f': {
 202                         const char *coeffstr = strtok(optarg, ":");
 203                         int coeff_index = 0;
 204                         while (coeff_index < NUM_FILTER_COEFF && coeffstr != NULL) {
 205                                 filter_coeff[coeff_index++] = atof(coeffstr);
 206                                 coeffstr = strtok(NULL, ":");
 207                         }
 208                         use_filter = true;
 209                         break;
 210                 }
 211
 212                 case 'F':
 213                         output_filtered = true;
 214                         break;
 215
 216                 case 'c': {
 217                         const char *cropstr = strtok(optarg, ":");
 218                         crop_start = atof(cropstr);
 219                         cropstr = strtok(NULL, ":");
 220                         if (cropstr == NULL) {
 221                                 crop_end = HUGE_VAL;
 222                         } else {
 223                                 crop_end = atof(cropstr);
 224                         }
 225                         do_crop = true;
 226                         break;
 227                 }
 228
 229                 case 'q':
 230                         quiet = true;
 231                         break;
 232
 233                 case 'h':
 234                 default:
 235                         help();
 236                         exit(1);
 237                 }
 238         }
 239 }
 240
 241 std::vector<float> crop(const std::vector<float>& pcm, float crop_start, float crop_end, int sample_rate)
 242 {
 243         size_t start_sample, end_sample;
 244         if (crop_start >= 0.0f) {
 245                 start_sample = std::min<size_t>(lrintf(crop_start * sample_rate), pcm.size());
 246         }
 247         if (crop_end >= 0.0f) {
 248                 end_sample = std::min<size_t>(lrintf(crop_end * sample_rate), pcm.size());
 249         }
 250         return std::vector<float>(pcm.begin() + start_sample, pcm.begin() + end_sample);
 251 }
 252
 253 // TODO: Support AVX here.
 254 std::vector<float> do_filter(const std::vector<float>& pcm, const float* filter)
 255 {
 256         std::vector<float> filtered_pcm;
 257         filtered_pcm.reserve(pcm.size());
 258         for (unsigned i = NUM_FILTER_COEFF; i < pcm.size(); ++i) {
 259                 float s = 0.0f;
 260                 for (int j = 0; j < NUM_FILTER_COEFF; ++j) {
 261                         s += filter[j] * pcm[i - j];
 262                 }
 263                 filtered_pcm.push_back(s);
 264         }
 265
 266         if (output_filtered) {
 267                 FILE *fp = fopen("filtered.raw", "wb");
 268                 fwrite(filtered_pcm.data(), filtered_pcm.size() * sizeof(filtered_pcm[0]), 1, fp);
 269                 fclose(fp);
 270         }
 271
 272         return filtered_pcm;
 273 }
 274
 275 std::vector<pulse> detect_pulses(const std::vector<float> &pcm, int sample_rate)
 276 {
 277         std::vector<pulse> pulses;
 278
 279         // Find the flanks.
 280         int last_bit = -1;
 281         double last_downflank = -1;
 282         for (unsigned i = 0; i < pcm.size(); ++i) {
 283                 int bit = (pcm[i] > 0) ? 1 : 0;
 284                 if (bit == 0 && last_bit == 1) {
 285                         // Check if we ever go up above <hysteresis_limit> before we dip down again.
 286                         bool true_pulse = false;
 287                         unsigned j;
 288                         int min_level_after = 32767;
 289                         for (j = i; j < pcm.size(); ++j) {
 290                                 min_level_after = std::min<int>(min_level_after, pcm[j]);
 291                                 if (pcm[j] > 0) break;
 292                                 if (pcm[j] < -hysteresis_limit) {
 293                                         true_pulse = true;
 294                                         break;
 295                                 }
 296                         }
 297
 298                         if (!true_pulse) {
 299 #if 0
 300                                 fprintf(stderr, "Ignored down-flank at %.6f seconds due to hysteresis (%d < %d).\n",
 301                                         double(i) / sample_rate, -min_level_after, hysteresis_limit);
 302 #endif
 303                                 i = j;
 304                                 continue;
 305                         }
 306
 307                         // down-flank!
 308                         double t = find_zerocrossing(pcm, i - 1) * (1.0 / sample_rate) + crop_start;
 309                         if (last_downflank > 0) {
 310                                 pulse p;
 311                                 p.time = t;
 312                                 p.len = t - last_downflank;
 313                                 pulses.push_back(p);
 314                         }
 315                         last_downflank = t;
 316                 }
 317                 last_bit = bit;
 318         }
 319         return pulses;
 320 }
 321
 322 int main(int argc, char **argv)
 323 {
 324         parse_options(argc, argv);
 325
 326         make_lanczos_weight_table();
 327         std::vector<float> pcm;
 328         int sample_rate;
 329         if (!read_audio_file(argv[optind], &pcm, &sample_rate)) {
 330                 exit(1);
 331         }
 332
 333         if (do_crop) {
 334                 pcm = crop(pcm, crop_start, crop_end, sample_rate);
 335         }
 336
 337         if (use_filter) {
 338                 pcm = do_filter(pcm, filter_coeff);
 339         }
 340
 341 #if 0
 342         for (int i = 0; i < LEN; ++i) {
 343                 in[i] += rand() % 10000;
 344         }
 345 #endif
 346
 347 #if 0
 348         for (int i = 0; i < LEN; ++i) {
 349                 printf("%d\n", in[i]);
 350         }
 351 #endif
 352
 353         std::vector<pulse> pulses = detect_pulses(pcm, sample_rate);
 354
 355         double calibration_factor = 1.0;
 356         if (do_calibrate) {
 357                 calibration_factor = calibrate(pulses);
 358         }
 359
 360         if (output_cycles_plot) {
 361                 FILE *fp = fopen("cycles.plot", "w");
 362                 for (unsigned i = 0; i < pulses.size(); ++i) {
 363                         double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 364                         fprintf(fp, "%f %f\n", pulses[i].time, cycles);
 365                 }
 366                 fclose(fp);
 367         }
 368
 369         output_tap(pulses, calibration_factor);
 370 }