cannam@126: /*
cannam@126: ** Copyright (c) 2002-2016, Erik de Castro Lopo <erikd@mega-nerd.com>
cannam@126: ** All rights reserved.
cannam@126: **
cannam@126: ** This code is released under 2-clause BSD license. Please see the
cannam@126: ** file at : https://github.com/erikd/libsamplerate/blob/master/COPYING
cannam@126: */
cannam@126: 
cannam@126: #include "config.h"
cannam@126: 
cannam@126: #include "util.h"
cannam@126: 
cannam@126: #if (HAVE_FFTW3 == 1)
cannam@126: 
cannam@126: #include <stdio.h>
cannam@126: #include <stdlib.h>
cannam@126: #include <string.h>
cannam@126: #include <math.h>
cannam@126: 
cannam@126: #include <fftw3.h>
cannam@126: 
cannam@126: #define	MAX_SPEC_LEN	(1<<18)
cannam@126: #define	MAX_PEAKS		10
cannam@126: 
cannam@126: static void log_mag_spectrum (double *input, int len, double *magnitude) ;
cannam@126: static void smooth_mag_spectrum (double *magnitude, int len) ;
cannam@126: static double find_snr (const double *magnitude, int len, int expected_peaks) ;
cannam@126: 
cannam@126: typedef struct
cannam@126: {	double	peak ;
cannam@126: 	int		index ;
cannam@126: } PEAK_DATA ;
cannam@126: 
cannam@126: double
cannam@126: calculate_snr (float *data, int len, int expected_peaks)
cannam@126: {	static double magnitude [MAX_SPEC_LEN] ;
cannam@126: 	static double datacopy [MAX_SPEC_LEN] ;
cannam@126: 
cannam@126: 	double snr = 200.0 ;
cannam@126: 	int k ;
cannam@126: 
cannam@126: 	if (len > MAX_SPEC_LEN)
cannam@126: 	{	printf ("%s : line %d : data length too large.\n", __FILE__, __LINE__) ;
cannam@126: 		exit (1) ;
cannam@126: 		} ;
cannam@126: 
cannam@126: 	for (k = 0 ; k < len ; k++)
cannam@126: 		datacopy [k] = data [k] ;
cannam@126: 
cannam@126: 	/* Pad the data just a little to speed up the FFT. */
cannam@126: 	while ((len & 0x1F) && len < MAX_SPEC_LEN)
cannam@126: 	{	datacopy [len] = 0.0 ;
cannam@126: 		len ++ ;
cannam@126: 		} ;
cannam@126: 
cannam@126: 	log_mag_spectrum (datacopy, len, magnitude) ;
cannam@126: 	smooth_mag_spectrum (magnitude, len / 2) ;
cannam@126: 
cannam@126: 	snr = find_snr (magnitude, len, expected_peaks) ;
cannam@126: 
cannam@126: 	return snr ;
cannam@126: } /* calculate_snr */
cannam@126: 
cannam@126: /*==============================================================================
cannam@126: ** There is a slight problem with trying to measure SNR with the method used
cannam@126: ** here; the side lobes of the windowed FFT can look like a noise/aliasing peak.
cannam@126: ** The solution is to smooth the magnitude spectrum by wiping out troughs
cannam@126: ** between adjacent peaks as done here.
cannam@126: ** This removes side lobe peaks without affecting noise/aliasing peaks.
cannam@126: */
cannam@126: 
cannam@126: static void linear_smooth (double *mag, PEAK_DATA *larger, PEAK_DATA *smaller) ;
cannam@126: 
cannam@126: static void
cannam@126: smooth_mag_spectrum (double *mag, int len)
cannam@126: {	PEAK_DATA peaks [2] ;
cannam@126: 
cannam@126: 	int k ;
cannam@126: 
cannam@126: 	memset (peaks, 0, sizeof (peaks)) ;
cannam@126: 
cannam@126: 	/* Find first peak. */
cannam@126: 	for (k = 1 ; k < len - 1 ; k++)
cannam@126: 	{	if (mag [k - 1] < mag [k] && mag [k] >= mag [k + 1])
cannam@126: 		{	peaks [0].peak = mag [k] ;
cannam@126: 			peaks [0].index = k ;
cannam@126: 			break ;
cannam@126: 			} ;
cannam@126: 		} ;
cannam@126: 
cannam@126: 	/* Find subsequent peaks ans smooth between peaks. */
cannam@126: 	for (k = peaks [0].index + 1 ; k < len - 1 ; k++)
cannam@126: 	{	if (mag [k - 1] < mag [k] && mag [k] >= mag [k + 1])
cannam@126: 		{	peaks [1].peak = mag [k] ;
cannam@126: 			peaks [1].index = k ;
cannam@126: 
cannam@126: 			if (peaks [1].peak > peaks [0].peak)
cannam@126: 				linear_smooth (mag, &peaks [1], &peaks [0]) ;
cannam@126: 			else
cannam@126: 				linear_smooth (mag, &peaks [0], &peaks [1]) ;
cannam@126: 			peaks [0] = peaks [1] ;
cannam@126: 			} ;
cannam@126: 		} ;
cannam@126: 
cannam@126: } /* smooth_mag_spectrum */
cannam@126: 
cannam@126: static void
cannam@126: linear_smooth (double *mag, PEAK_DATA *larger, PEAK_DATA *smaller)
cannam@126: {	int k ;
cannam@126: 
cannam@126: 	if (smaller->index < larger->index)
cannam@126: 	{	for (k = smaller->index + 1 ; k < larger->index ; k++)
cannam@126: 			mag [k] = (mag [k] < mag [k - 1]) ? 0.999 * mag [k - 1] : mag [k] ;
cannam@126: 		}
cannam@126: 	else
cannam@126: 	{	for (k = smaller->index - 1 ; k >= larger->index ; k--)
cannam@126: 			mag [k] = (mag [k] < mag [k + 1]) ? 0.999 * mag [k + 1] : mag [k] ;
cannam@126: 		} ;
cannam@126: 
cannam@126: } /* linear_smooth */
cannam@126: 
cannam@126: /*==============================================================================
cannam@126: */
cannam@126: 
cannam@126: static int
cannam@126: peak_compare (const void *vp1, const void *vp2)
cannam@126: {	const PEAK_DATA *peak1, *peak2 ;
cannam@126: 
cannam@126: 	peak1 = (const PEAK_DATA*) vp1 ;
cannam@126: 	peak2 = (const PEAK_DATA*) vp2 ;
cannam@126: 
cannam@126: 	return (peak1->peak < peak2->peak) ? 1 : -1 ;
cannam@126: } /* peak_compare */
cannam@126: 
cannam@126: static double
cannam@126: find_snr (const double *magnitude, int len, int expected_peaks)
cannam@126: {	PEAK_DATA peaks [MAX_PEAKS] ;
cannam@126: 
cannam@126: 	int		k, peak_count = 0 ;
cannam@126: 	double	snr ;
cannam@126: 
cannam@126: 	memset (peaks, 0, sizeof (peaks)) ;
cannam@126: 
cannam@126: 	/* Find the MAX_PEAKS largest peaks. */
cannam@126: 	for (k = 1 ; k < len - 1 ; k++)
cannam@126: 	{	if (magnitude [k - 1] < magnitude [k] && magnitude [k] >= magnitude [k + 1])
cannam@126: 		{	if (peak_count < MAX_PEAKS)
cannam@126: 			{	peaks [peak_count].peak = magnitude [k] ;
cannam@126: 				peaks [peak_count].index = k ;
cannam@126: 				peak_count ++ ;
cannam@126: 				qsort (peaks, peak_count, sizeof (PEAK_DATA), peak_compare) ;
cannam@126: 				}
cannam@126: 			else if (magnitude [k] > peaks [MAX_PEAKS - 1].peak)
cannam@126: 			{	peaks [MAX_PEAKS - 1].peak = magnitude [k] ;
cannam@126: 				peaks [MAX_PEAKS - 1].index = k ;
cannam@126: 				qsort (peaks, MAX_PEAKS, sizeof (PEAK_DATA), peak_compare) ;
cannam@126: 				} ;
cannam@126: 			} ;
cannam@126: 		} ;
cannam@126: 
cannam@126: 	if (peak_count < expected_peaks)
cannam@126: 	{	printf ("\n%s : line %d : bad peak_count (%d), expected %d.\n\n", __FILE__, __LINE__, peak_count, expected_peaks) ;
cannam@126: 		return -1.0 ;
cannam@126: 		} ;
cannam@126: 
cannam@126: 	/* Sort the peaks. */
cannam@126: 	qsort (peaks, peak_count, sizeof (PEAK_DATA), peak_compare) ;
cannam@126: 
cannam@126: 	snr = peaks [0].peak ;
cannam@126: 	for (k = 1 ; k < peak_count ; k++)
cannam@126: 		if (fabs (snr - peaks [k].peak) > 10.0)
cannam@126: 			return fabs (peaks [k].peak) ;
cannam@126: 
cannam@126: 	return snr ;
cannam@126: } /* find_snr */
cannam@126: 
cannam@126: static void
cannam@126: log_mag_spectrum (double *input, int len, double *magnitude)
cannam@126: {	fftw_plan plan = NULL ;
cannam@126: 
cannam@126: 	double	maxval ;
cannam@126: 	int		k ;
cannam@126: 
cannam@126: 	if (input == NULL || magnitude == NULL)
cannam@126: 		return ;
cannam@126: 
cannam@126: 	plan = fftw_plan_r2r_1d (len, input, magnitude, FFTW_R2HC, FFTW_ESTIMATE | FFTW_PRESERVE_INPUT) ;
cannam@126: 	if (plan == NULL)
cannam@126: 	{	printf ("%s : line %d : create plan failed.\n", __FILE__, __LINE__) ;
cannam@126: 		exit (1) ;
cannam@126: 		} ;
cannam@126: 
cannam@126: 	fftw_execute (plan) ;
cannam@126: 
cannam@126: 	fftw_destroy_plan (plan) ;
cannam@126: 
cannam@126: 	maxval = 0.0 ;
cannam@126: 	for (k = 1 ; k < len / 2 ; k++)
cannam@126: 	{	/*
cannam@126: 		** From : http://www.fftw.org/doc/Real_002dto_002dReal-Transform-Kinds.html#Real_002dto_002dReal-Transform-Kinds
cannam@126: 		**
cannam@126: 		** FFTW_R2HC computes a real-input DFT with output in “halfcomplex” format, i.e. real and imaginary parts
cannam@126: 		** for a transform of size n stored as:
cannam@126: 		**
cannam@126: 		**      r0, r1, r2, ..., rn/2, i(n+1)/2-1, ..., i2, i1
cannam@126: 		*/
cannam@126: 		double re = magnitude [k] ;
cannam@126: 		double im = magnitude [len - k] ;
cannam@126: 		magnitude [k] = sqrt (re * re + im * im) ;
cannam@126: 		maxval = (maxval < magnitude [k]) ? magnitude [k] : maxval ;
cannam@126: 		} ;
cannam@126: 
cannam@126: 	memset (magnitude + len / 2, 0, len / 2 * sizeof (magnitude [0])) ;
cannam@126: 
cannam@126: 	/* Don't care about DC component. Make it zero. */
cannam@126: 	magnitude [0] = 0.0 ;
cannam@126: 
cannam@126: 	/* log magnitude. */
cannam@126: 	for (k = 0 ; k < len ; k++)
cannam@126: 	{	magnitude [k] = magnitude [k] / maxval ;
cannam@126: 		magnitude [k] = (magnitude [k] < 1e-15) ? -200.0 : 20.0 * log10 (magnitude [k]) ;
cannam@126: 		} ;
cannam@126: 
cannam@126: 	return ;
cannam@126: } /* log_mag_spectrum */
cannam@126: 
cannam@126: #else /* ! (HAVE_LIBFFTW && HAVE_LIBRFFTW) */
cannam@126: 
cannam@126: double
cannam@126: calculate_snr (float *data, int len, int expected_peaks)
cannam@126: {	double snr = 200.0 ;
cannam@126: 
cannam@126: 	data = data ;
cannam@126: 	len = len ;
cannam@126: 	expected_peaks = expected_peaks ;
cannam@126: 
cannam@126: 	return snr ;
cannam@126: } /* calculate_snr */
cannam@126: 
cannam@126: #endif
cannam@126: