#include <vector>
#include <algorithm>
-#define LANCZOS_RADIUS 30
+#include "interpolate.h"
+
#define BUFSIZE 4096
#define HYSTERESIS_LIMIT 3000
#define SAMPLE_RATE 44100
#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 {
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)
{
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;
+ double upper = x;
+ double lower = 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;
// Find the flanks.
int last_bit = -1;
- double last_upflank = -1;
+ 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) {
+ 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 max_level_after = -32768;
+ int min_level_after = 32767;
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) {
+ 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 (!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);
+ 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;
}
- // up-flank!
+ // down-flank!
double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
- if (last_upflank > 0) {
+ 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_downflank = t;
}
last_bit = bit;
}
}
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) {
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",
+ fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
pulses[i].time, cycles);
}
}
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) {