kopia lustrzana https://github.com/windytan/slowrx
248 wiersze
6.6 KiB
C
248 wiersze
6.6 KiB
C
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#include <stdlib.h>
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#include <math.h>
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#include <fftw3.h>
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#include <gtk/gtk.h>
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#include "common.h"
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/* Find the horizontal sync signal and adjust sample rate to cancel out any slant.
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* Length: number of PCM samples to process
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* Mode: one of M1, M2, S1, S2, R72, R36 ...
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* Rate: approximate sampling rate used
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* Skip: pointer to variable where the skip amount will be returned
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* returns adjusted sample rate
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*/
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double FindSync (unsigned int Length, int Mode, double Rate, int *Skip) {
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unsigned int i, s, j, TotPix;
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double NextImgSample;
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double t=0, slantAngle;
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unsigned short int SyncImg[700][500];
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int x,y;
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double Praw, Psync;
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char *HasSync;
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HasSync = malloc(Length * sizeof(char));
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if (HasSync == NULL) {
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perror("FindSync: Unable to allocate memory for sync signal\n");
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exit(EXIT_FAILURE);
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}
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unsigned short int *lines;
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lines = calloc(3000*720, sizeof(unsigned short int));
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if (HasSync == NULL) {
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perror("FindSync: Unable to allocate memory for Hough transform\n");
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exit(EXIT_FAILURE);
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}
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unsigned short int cy, cx;
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int q, d, qMost, dMost;
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unsigned short int Retries = 0;
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int maxsy = 0;
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FILE *GrayFile;
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char PixBuf[1] = {0};
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unsigned short int xAcc[700] = {0};
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unsigned short int xMax = 0;
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unsigned short int Leftmost;
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// FFT plan
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fftw_plan Plan;
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double *in;
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double *out;
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unsigned int FFTLen = 1024;
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in = fftw_malloc(sizeof(double) * FFTLen);
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if (in == NULL) {
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perror("FindSync: Unable to allocate memory for FFT\n");
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free(HasSync);
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exit(EXIT_FAILURE);
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}
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out = fftw_malloc(sizeof(double) * FFTLen);
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if (out == NULL) {
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perror("FindSync: Unable to allocate memory for FFT\n");
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fftw_free(in);
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free(HasSync);
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exit(EXIT_FAILURE);
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}
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Plan = fftw_plan_r2r_1d(FFTLen, in, out, FFTW_FORWARD, FFTW_ESTIMATE);
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// Create 50-point Hann window
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double Hann[50] = {0};
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for (i = 0; i < 50; i++) Hann[i] = 0.5 * (1 - cos( 2 * M_PI * i / 49.0) );
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// Zero fill input array
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for (i = 0; i < FFTLen; i++) in[i] = 0;
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// Power estimation
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for (s = 0; s < Length; s+=50) {
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// Hann window
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for (i = 0; i < 50; i++) in[i] = PCM[s+i] * 32768 * Hann[i];
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// FFT
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fftw_execute(Plan);
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// Power in raw band
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i = GetBin(700+HedrShift, FFTLen, 44100);
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Praw = (pow(out[i-1], 2) + pow(out[FFTLen - (i-1)], 2) +
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pow(out[i], 2) + pow(out[FFTLen - i], 2) +
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pow(out[i+1], 2) + pow(out[FFTLen - (i+1)], 2)) / 3.0;
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// Power in the sync band
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i = GetBin(1200+HedrShift, FFTLen, 44100);
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Psync = pow(out[i], 2) + pow(out[FFTLen - i], 2);
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// If there is more than twice the amount of Power per Hz in the
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// sync band than in the empty band, we have a sync signal here
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if (Psync > 2*Praw) HasSync[s] = TRUE;
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else HasSync[s] = FALSE;
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HasSync[s] = !HasSync[s]; // Bug: Otherwise would produce reverse grayscale!
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for (i = 0; i < 50; i++) {
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if (s+i >= Length) break;
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HasSync[s+i] = HasSync[s];
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}
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}
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// Repeat until slant < 0.5° or until we give up
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while (1) {
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GrayFile = fopen("sync.gray","w");
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TotPix = 0;
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NextImgSample = 0;
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t = 0;
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maxsy = 0;
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for (i=0;i<700;i++)
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for (j=0;j<500;j++)
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SyncImg[i][j] = 0;
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// Draw the sync signal into memory
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for (s = 0; s < Length; s++) {
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// t keeps track of time in seconds
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t += 1.0/Rate;
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if (t >= NextImgSample) {
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x = TotPix % 700;
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y = TotPix / 700;
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SyncImg[x][y] = HasSync[s];
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if (y > maxsy) maxsy = y;
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PixBuf[0] = (SyncImg[x][y] ? 255 : 0);
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fwrite(PixBuf, 1, 1, GrayFile);
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TotPix++;
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NextImgSample += ModeSpec[Mode].LineLen / 700.0;
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}
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}
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fclose(GrayFile);
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/** Linear Hough transform **/
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// zero arrays
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dMost = qMost = 0;
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for (d=0;d<3000;d++)
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for (q=MINSLANT*2; q <= MAXSLANT * 2; q++)
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lines[d*720 + q] = 0;
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// Find white pixels that likely belong to the left edge of a sync pulse
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for (cy = 0; cy < TotPix / 700; cy++) {
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for (cx = 0; cx < 700; cx++) {
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if (cx > 0 && cx < 697 && !SyncImg[cx - 1][cy] && SyncImg[cx][cy]) {
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// Slant angles to consider
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for (q = MINSLANT*2; q <= MAXSLANT*2; q ++) {
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// Find the line parameters with most occurrences
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d = round( -cx * sin(deg2rad(q/2.0)) + cy * cos(deg2rad(q/2.0)) );
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d = abs(d+2000);
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if (d<0) d = 0;
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if (d>2999) d = 2999;
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lines[d*720 + q] ++;
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if (lines[d*720 + q] > lines[dMost*720 + qMost]) {
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dMost = d;
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qMost = q;
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}
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}
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}
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}
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}
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if ( qMost == 0) {
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printf(" no sync signal; giving up\n");
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break;
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}
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slantAngle = qMost / 2.0;
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//printf(" most (%d occurrences): d=%d q=%f\n", LineAcc[dMost][ (int)(qMost * 10) ], dMost, qMost);
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printf(" %.1f° @ %.2f Hz", 90 - slantAngle, Rate);
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Rate = Rate + tan(deg2rad(90 - slantAngle)) / 700.0 * Rate;
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if (Rate < 40000 || Rate > 50000) {
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printf(" unrealistic receiving conditions; giving up.\n");
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Rate = 44100;
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break;
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}
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if (slantAngle > 89 && slantAngle < 91) {
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printf(" -> %.2f slant OK :)\n", Rate);
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break;
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} else if (Retries == 3) {
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printf(" still slanted; giving up\n");
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Rate = 44100;
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printf(" -> 44100\n");
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break;
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} else {
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printf(" -> %.2f still slanted; retrying\n", Rate);
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Retries ++;
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}
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}
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free(lines);
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printf(" gray = %dx%d\n", 700, maxsy);
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// Find the abscissa of the now vertical sync pulse
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for (i=0;i<700;i++) xAcc[i] = 0;
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xMax = 0;
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for (cy = 0; cy < TotPix / 700; cy++) {
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for (cx = 1; cx < 700; cx++) {
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if (!SyncImg[cx - 1][cy] && SyncImg[cx][cy]) {
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xAcc[cx]++;
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if (xAcc[cx] > xAcc[xMax]) xMax = cx;
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}
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}
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}
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// Now, find the leftmost one of those vertical lines with the maximum occurrences
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Leftmost = 700;
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for (i = 0; i < 700; i++) {
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if (xAcc[i] == xAcc[xMax] && i < Leftmost) Leftmost = i;
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}
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if (Rate == 44100) Leftmost = 0;
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printf(" abscissa = %d (%d occurrences)", Leftmost, xAcc[Leftmost]);
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Leftmost = Leftmost * (ModeSpec[Mode].LineLen / 700.0) * Rate;
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printf(" (need to skip %d samples)\n", Leftmost);
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*Skip = Leftmost;
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free(HasSync);
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fftw_destroy_plan(Plan);
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fftw_free(in);
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fftw_free(out);
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return (Rate);
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}
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