X-Git-Url: https://git.sesse.net/?p=c64tapwav;a=blobdiff_plain;f=decode.cpp;h=8ed2f1b4e7714c9d3a8776aec9e26e30ee142b41;hp=7bbb250f973ce0f307bd3062e45573b7a11a90d9;hb=d693db9567105ab7837addb952c2553d2dfa9543;hpb=1dcf7f3a51d75ac55569e68dcce57375bfa971bb diff --git a/decode.cpp b/decode.cpp index 7bbb250..8ed2f1b 100644 --- a/decode.cpp +++ b/decode.cpp @@ -1,69 +1,24 @@ #include #include #include -#include #include +#include #include #include -#define LANCZOS_RADIUS 30 +#include "audioreader.h" +#include "interpolate.h" +#include "tap.h" + #define BUFSIZE 4096 #define HYSTERESIS_LIMIT 3000 -#define SAMPLE_RATE 44100 #define C64_FREQUENCY 985248 -#define TAP_RESOLUTION 8 #define SYNC_PULSE_START 1000 -#define SYNC_PULSE_END 15000 -#define SYNC_PULSE_LENGTH 380.0 +#define SYNC_PULSE_END 20000 +#define SYNC_PULSE_LENGTH 378.0 #define SYNC_TEST_TOLERANCE 1.10 -struct tap_header { - char identifier[12]; - char version; - char reserved[3]; - unsigned int data_len; -}; - -double sinc(double x) -{ - if (fabs(x) < 1e-6) { - return 1.0f - fabs(x); - } else { - return sin(x) / x; - } -} - -#if 1 -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 &pcm, double i) -{ - int lower = std::max(ceil(i - LANCZOS_RADIUS), 0); - int upper = std::min(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 &pcm, int x) { @@ -74,14 +29,14 @@ double find_zerocrossing(const std::vector &pcm, int x) return x + 1; } - assert(pcm[x + 1] > 0); - assert(pcm[x] < 0); + assert(pcm[x + 1] < 0); + assert(pcm[x] > 0); - double lower = x; - double upper = x + 1; - while (upper - lower > 1e-6) { + double upper = x; + double lower = x + 1; + while (lower - upper > 1e-3) { double mid = 0.5f * (upper + lower); - if (interpolate(pcm, mid) > 0) { + if (lanczos_interpolate(pcm, mid) > 0) { upper = mid; } else { lower = mid; @@ -95,18 +50,68 @@ struct pulse { double time; // in seconds from start double len; // in seconds }; + +// Calibrate on the first ~25k pulses (skip a few, just to be sure). +double calibrate(const std::vector &pulses) { + if (pulses.size() < SYNC_PULSE_END) { + fprintf(stderr, "Too few pulses, not calibrating!\n"); + return 1.0; + } + + int sync_pulse_end = -1; + double sync_pulse_stddev = -1.0; + + // Compute the standard deviation (to check for uneven speeds). + // If it suddenly skyrockets, we assume that sync ended earlier + // than we thought (it should be 25000 cycles), and that we should + // calibrate on fewer cycles. + for (int try_end : { 2000, 4000, 5000, 7500, 10000, 15000, SYNC_PULSE_END }) { + double sum2 = 0.0; + for (int i = SYNC_PULSE_START; i < try_end; ++i) { + double cycles = pulses[i].len * C64_FREQUENCY; + sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH); + } + double stddev = sqrt(sum2 / (try_end - SYNC_PULSE_START - 1)); + if (sync_pulse_end != -1 && stddev > 5.0 && stddev / sync_pulse_stddev > 1.3) { + fprintf(stderr, "Stopping at %d sync pulses because standard deviation would be too big (%.2f cycles); shorter-than-usual trailer?\n", + sync_pulse_end, stddev); + break; + } + sync_pulse_end = try_end; + sync_pulse_stddev = stddev; + } + fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n", + sync_pulse_stddev); + + double sum = 0.0; + for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) { + sum += pulses[i].len; + } + double mean_length = C64_FREQUENCY * sum / (sync_pulse_end - SYNC_PULSE_START); + double calibration_factor = SYNC_PULSE_LENGTH / mean_length; + 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) { + double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY; + if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) { + fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n", + pulses[i].time, cycles); + } + } + + return calibration_factor; +} int main(int argc, char **argv) { + make_lanczos_weight_table(); std::vector pcm; - - while (!feof(stdin)) { - short buf[BUFSIZE]; - ssize_t ret = fread(buf, 2, BUFSIZE, stdin); - if (ret >= 0) { - pcm.insert(pcm.end(), buf, buf + ret); - } - } + int sample_rate; + if (!read_audio_file(argv[1], &pcm, &sample_rate)) { + exit(1); + } #if 0 for (int i = 0; i < LEN; ++i) { @@ -124,66 +129,55 @@ int main(int argc, char **argv) // Find the flanks. int last_bit = -1; - double last_upflank = -1; - int last_max_level = 0; + double last_downflank = -1; 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) { - // up-flank! - double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE); - if (last_upflank > 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(min_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 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); + if (last_downflank > 0) { pulse p; p.time = t; - p.len = t - last_upflank; + p.len = t - last_downflank; pulses.push_back(p); } - last_upflank = t; - last_max_level = 0; + last_downflank = t; } - last_max_level = std::max(last_max_level, abs(pcm[i])); last_bit = bit; } - // Calibrate on the first ~25k pulses (skip a few, just to be sure). - double calibration_factor = 1.0f; - if (pulses.size() < SYNC_PULSE_END) { - fprintf(stderr, "Too few pulses, not calibrating!\n"); - } else { - double sum = 0.0; - for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) { - sum += pulses[i].len; - } - 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)); - - // Check for pulses outside +/- 10% (sign of misdetection). - for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) { - double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY; - if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) { - fprintf(stderr, "Sync cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n", - pulses[i].time, cycles); - } - } - - // Compute the standard deviation (to check for uneven speeds). - double sum2 = 0.0; - for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) { - double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY; - sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH); - } - double stddev = sqrt(sum2 / (SYNC_PULSE_END - SYNC_PULSE_START - 1)); - fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n", - stddev); - } + double calibration_factor = calibrate(pulses); + FILE *fp = fopen("cycles.plot", "w"); std::vector tap_data; for (unsigned i = 0; i < pulses.size(); ++i) { double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY; + fprintf(fp, "%f %f\n", pulses[i].time, cycles); int len = lrintf(cycles / TAP_RESOLUTION); if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) { - fprintf(stderr, "Cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n", + fprintf(stderr, "Cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n", pulses[i].time, cycles); } if (len <= 255) { @@ -196,6 +190,7 @@ int main(int argc, char **argv) tap_data.push_back(overflow_len >> 16); } } + fclose(fp); tap_header hdr; memcpy(hdr.identifier, "C64-TAPE-RAW", 12); @@ -205,4 +200,20 @@ int main(int argc, char **argv) fwrite(&hdr, sizeof(hdr), 1, stdout); fwrite(tap_data.data(), tap_data.size(), 1, stdout); + + // Output a debug raw file with pulse detection points. + fp = fopen("debug.raw", "wb"); + short one = 32767; + short zero = 0; + unsigned pulsenum = 0; + for (unsigned i = 0; i < pcm.size(); ++i) { + unsigned next_pulse = (pulsenum >= pulses.size()) ? INT_MAX : int(pulses[pulsenum].time * sample_rate); + if (i >= next_pulse) { + fwrite(&one, sizeof(one), 1, fp); + ++pulsenum; + } else { + fwrite(&zero, sizeof(zero), 1, fp); + } + } + fclose(fp); }