--- /dev/null
+/*
+** Copyright (c) 2002-2016, Erik de Castro Lopo <erikd@mega-nerd.com>
+** All rights reserved.
+**
+** This code is released under 2-clause BSD license. Please see the
+** file at : https://github.com/erikd/libsamplerate/blob/master/COPYING
+*/
+
+#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) ;
+
+ maxval = 0.0 ;
+ for (k = 1 ; k < len / 2 ; k++)
+ { /*
+ ** From : http://www.fftw.org/doc/Real_002dto_002dReal-Transform-Kinds.html#Real_002dto_002dReal-Transform-Kinds
+ **
+ ** FFTW_R2HC computes a real-input DFT with output in “halfcomplex” format, i.e. real and imaginary parts
+ ** for a transform of size n stored as:
+ **
+ ** r0, r1, r2, ..., rn/2, i(n+1)/2-1, ..., i2, i1
+ */
+ double re = magnitude [k] ;
+ double im = magnitude [len - k] ;
+ magnitude [k] = sqrt (re * re + im * im) ;
+ 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
+
projects / audio-libsamplerate.git / blobdiff