| /* |
| ** Copyright (C) 2002-2011 Erik de Castro Lopo <erikd@mega-nerd.com> |
| ** |
| ** This program is free software; you can redistribute it and/or modify |
| ** it under the terms of the GNU General Public License as published by |
| ** the Free Software Foundation; either version 2 of the License, or |
| ** (at your option) any later version. |
| ** |
| ** This program is distributed in the hope that it will be useful, |
| ** but WITHOUT ANY WARRANTY; without even the implied warranty of |
| ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| ** GNU General Public License for more details. |
| ** |
| ** You should have received a copy of the GNU General Public License |
| ** along with this program; if not, write to the Free Software |
| ** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA. |
| */ |
| |
| #include "config.h" |
| |
| #include "util.h" |
| |
| #if (HAVE_FFTW3 == 1) |
| |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <math.h> |
| |
| #include <fftw3.h> |
| |
| #define MAX_SPEC_LEN (1<<18) |
| #define MAX_PEAKS 10 |
| |
| static void log_mag_spectrum (double *input, int len, double *magnitude) ; |
| static void smooth_mag_spectrum (double *magnitude, int len) ; |
| static double find_snr (const double *magnitude, int len, int expected_peaks) ; |
| |
| typedef struct |
| { double peak ; |
| int index ; |
| } PEAK_DATA ; |
| |
| double |
| calculate_snr (float *data, int len, int expected_peaks) |
| { static double magnitude [MAX_SPEC_LEN] ; |
| static double datacopy [MAX_SPEC_LEN] ; |
| |
| double snr = 200.0 ; |
| int k ; |
| |
| if (len > MAX_SPEC_LEN) |
| { printf ("%s : line %d : data length too large.\n", __FILE__, __LINE__) ; |
| exit (1) ; |
| } ; |
| |
| for (k = 0 ; k < len ; k++) |
| datacopy [k] = data [k] ; |
| |
| /* Pad the data just a little to speed up the FFT. */ |
| while ((len & 0x1F) && len < MAX_SPEC_LEN) |
| { datacopy [len] = 0.0 ; |
| len ++ ; |
| } ; |
| |
| log_mag_spectrum (datacopy, len, magnitude) ; |
| smooth_mag_spectrum (magnitude, len / 2) ; |
| |
| snr = find_snr (magnitude, len, expected_peaks) ; |
| |
| return snr ; |
| } /* calculate_snr */ |
| |
| /*============================================================================== |
| ** There is a slight problem with trying to measure SNR with the method used |
| ** here; the side lobes of the windowed FFT can look like a noise/aliasing peak. |
| ** The solution is to smooth the magnitude spectrum by wiping out troughs |
| ** between adjacent peaks as done here. |
| ** This removes side lobe peaks without affecting noise/aliasing peaks. |
| */ |
| |
| static void linear_smooth (double *mag, PEAK_DATA *larger, PEAK_DATA *smaller) ; |
| |
| static void |
| smooth_mag_spectrum (double *mag, int len) |
| { PEAK_DATA peaks [2] ; |
| |
| int k ; |
| |
| memset (peaks, 0, sizeof (peaks)) ; |
| |
| /* Find first peak. */ |
| for (k = 1 ; k < len - 1 ; k++) |
| { if (mag [k - 1] < mag [k] && mag [k] >= mag [k + 1]) |
| { peaks [0].peak = mag [k] ; |
| peaks [0].index = k ; |
| break ; |
| } ; |
| } ; |
| |
| /* Find subsequent peaks ans smooth between peaks. */ |
| for (k = peaks [0].index + 1 ; k < len - 1 ; k++) |
| { if (mag [k - 1] < mag [k] && mag [k] >= mag [k + 1]) |
| { peaks [1].peak = mag [k] ; |
| peaks [1].index = k ; |
| |
| if (peaks [1].peak > peaks [0].peak) |
| linear_smooth (mag, &peaks [1], &peaks [0]) ; |
| else |
| linear_smooth (mag, &peaks [0], &peaks [1]) ; |
| peaks [0] = peaks [1] ; |
| } ; |
| } ; |
| |
| } /* smooth_mag_spectrum */ |
| |
| static void |
| linear_smooth (double *mag, PEAK_DATA *larger, PEAK_DATA *smaller) |
| { int k ; |
| |
| if (smaller->index < larger->index) |
| { for (k = smaller->index + 1 ; k < larger->index ; k++) |
| mag [k] = (mag [k] < mag [k - 1]) ? 0.999 * mag [k - 1] : mag [k] ; |
| } |
| else |
| { for (k = smaller->index - 1 ; k >= larger->index ; k--) |
| mag [k] = (mag [k] < mag [k + 1]) ? 0.999 * mag [k + 1] : mag [k] ; |
| } ; |
| |
| } /* linear_smooth */ |
| |
| /*============================================================================== |
| */ |
| |
| static int |
| peak_compare (const void *vp1, const void *vp2) |
| { const PEAK_DATA *peak1, *peak2 ; |
| |
| peak1 = (const PEAK_DATA*) vp1 ; |
| peak2 = (const PEAK_DATA*) vp2 ; |
| |
| return (peak1->peak < peak2->peak) ? 1 : -1 ; |
| } /* peak_compare */ |
| |
| static double |
| find_snr (const double *magnitude, int len, int expected_peaks) |
| { PEAK_DATA peaks [MAX_PEAKS] ; |
| |
| int k, peak_count = 0 ; |
| double snr ; |
| |
| memset (peaks, 0, sizeof (peaks)) ; |
| |
| /* Find the MAX_PEAKS largest peaks. */ |
| for (k = 1 ; k < len - 1 ; k++) |
| { if (magnitude [k - 1] < magnitude [k] && magnitude [k] >= magnitude [k + 1]) |
| { if (peak_count < MAX_PEAKS) |
| { peaks [peak_count].peak = magnitude [k] ; |
| peaks [peak_count].index = k ; |
| peak_count ++ ; |
| qsort (peaks, peak_count, sizeof (PEAK_DATA), peak_compare) ; |
| } |
| else if (magnitude [k] > peaks [MAX_PEAKS - 1].peak) |
| { peaks [MAX_PEAKS - 1].peak = magnitude [k] ; |
| peaks [MAX_PEAKS - 1].index = k ; |
| qsort (peaks, MAX_PEAKS, sizeof (PEAK_DATA), peak_compare) ; |
| } ; |
| } ; |
| } ; |
| |
| if (peak_count < expected_peaks) |
| { printf ("\n%s : line %d : bad peak_count (%d), expected %d.\n\n", __FILE__, __LINE__, peak_count, expected_peaks) ; |
| return -1.0 ; |
| } ; |
| |
| /* Sort the peaks. */ |
| qsort (peaks, peak_count, sizeof (PEAK_DATA), peak_compare) ; |
| |
| snr = peaks [0].peak ; |
| for (k = 1 ; k < peak_count ; k++) |
| if (fabs (snr - peaks [k].peak) > 10.0) |
| return fabs (peaks [k].peak) ; |
| |
| return snr ; |
| } /* find_snr */ |
| |
| static void |
| log_mag_spectrum (double *input, int len, double *magnitude) |
| { fftw_plan plan = NULL ; |
| |
| double maxval ; |
| int k ; |
| |
| if (input == NULL || magnitude == NULL) |
| return ; |
| |
| plan = fftw_plan_r2r_1d (len, input, magnitude, FFTW_R2HC, FFTW_ESTIMATE | FFTW_PRESERVE_INPUT) ; |
| if (plan == NULL) |
| { printf ("%s : line %d : create plan failed.\n", __FILE__, __LINE__) ; |
| exit (1) ; |
| } ; |
| |
| fftw_execute (plan) ; |
| |
| fftw_destroy_plan (plan) ; |
| |
| /* (k < N/2 rounded up) */ |
| maxval = 0.0 ; |
| for (k = 1 ; k < len / 2 ; k++) |
| { magnitude [k] = sqrt (magnitude [k] * magnitude [k] + magnitude [len - k - 1] * magnitude [len - k - 1]) ; |
| maxval = (maxval < magnitude [k]) ? magnitude [k] : maxval ; |
| } ; |
| |
| memset (magnitude + len / 2, 0, len / 2 * sizeof (magnitude [0])) ; |
| |
| /* Don't care about DC component. Make it zero. */ |
| magnitude [0] = 0.0 ; |
| |
| /* log magnitude. */ |
| for (k = 0 ; k < len ; k++) |
| { magnitude [k] = magnitude [k] / maxval ; |
| magnitude [k] = (magnitude [k] < 1e-15) ? -200.0 : 20.0 * log10 (magnitude [k]) ; |
| } ; |
| |
| return ; |
| } /* log_mag_spectrum */ |
| |
| #else /* ! (HAVE_LIBFFTW && HAVE_LIBRFFTW) */ |
| |
| double |
| calculate_snr (float *data, int len, int expected_peaks) |
| { double snr = 200.0 ; |
| |
| data = data ; |
| len = len ; |
| expected_peaks = expected_peaks ; |
| |
| return snr ; |
| } /* calculate_snr */ |
| |
| #endif |
| |