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freeswitch/libs/libcodec2/src/nlp.c
Brian West 62b55523c2 Working codec2 support
2010-09-21 12:35:41 -05:00

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/*---------------------------------------------------------------------------*\
FILE........: nlp.c
AUTHOR......: David Rowe
DATE CREATED: 23/3/93
Non Linear Pitch (NLP) estimation functions.
\*---------------------------------------------------------------------------*/
/*
Copyright (C) 2009 David Rowe
All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License version 2.1, as
published by the Free Software Foundation. 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 Lesser General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include "defines.h"
#include "nlp.h"
#include "dump.h"
#include "four1.h"
#include <assert.h>
#include <math.h>
#include <stdlib.h>
/*---------------------------------------------------------------------------*\
DEFINES
\*---------------------------------------------------------------------------*/
#define PMAX_M 600 /* maximum NLP analysis window size */
#define COEFF 0.95 /* notch filter parameter */
#define PE_FFT_SIZE 512 /* DFT size for pitch estimation */
#define DEC 5 /* decimation factor */
#define SAMPLE_RATE 8000
#define PI 3.141592654 /* mathematical constant */
#define T 0.1 /* threshold for local minima candidate */
#define F0_MAX 500
#define CNLP 0.3 /* post processor constant */
#define NLP_NTAP 48 /* Decimation LPF order */
/*---------------------------------------------------------------------------*\
GLOBALS
\*---------------------------------------------------------------------------*/
/* 48 tap 600Hz low pass FIR filter coefficients */
float nlp_fir[] = {
-1.0818124e-03,
-1.1008344e-03,
-9.2768838e-04,
-4.2289438e-04,
5.5034190e-04,
2.0029849e-03,
3.7058509e-03,
5.1449415e-03,
5.5924666e-03,
4.3036754e-03,
8.0284511e-04,
-4.8204610e-03,
-1.1705810e-02,
-1.8199275e-02,
-2.2065282e-02,
-2.0920610e-02,
-1.2808831e-02,
3.2204775e-03,
2.6683811e-02,
5.5520624e-02,
8.6305944e-02,
1.1480192e-01,
1.3674206e-01,
1.4867556e-01,
1.4867556e-01,
1.3674206e-01,
1.1480192e-01,
8.6305944e-02,
5.5520624e-02,
2.6683811e-02,
3.2204775e-03,
-1.2808831e-02,
-2.0920610e-02,
-2.2065282e-02,
-1.8199275e-02,
-1.1705810e-02,
-4.8204610e-03,
8.0284511e-04,
4.3036754e-03,
5.5924666e-03,
5.1449415e-03,
3.7058509e-03,
2.0029849e-03,
5.5034190e-04,
-4.2289438e-04,
-9.2768838e-04,
-1.1008344e-03,
-1.0818124e-03
};
typedef struct {
float sq[PMAX_M]; /* squared speech samples */
float mem_x,mem_y; /* memory for notch filter */
float mem_fir[NLP_NTAP]; /* decimation FIR filter memory */
} NLP;
float post_process_mbe(COMP Fw[], int pmin, int pmax, float gmax);
float post_process_sub_multiples(COMP Fw[],
int pmin, int pmax, float gmax, int gmax_bin,
float *prev_Wo);
/*---------------------------------------------------------------------------*\
nlp_create()
Initialisation function for NLP pitch estimator.
\*---------------------------------------------------------------------------*/
void *nlp_create()
{
NLP *nlp;
int i;
nlp = (NLP*)malloc(sizeof(NLP));
if (nlp == NULL)
return NULL;
for(i=0; i<PMAX_M; i++)
nlp->sq[i] = 0.0;
nlp->mem_x = 0.0;
nlp->mem_y = 0.0;
for(i=0; i<NLP_NTAP; i++)
nlp->mem_fir[i] = 0.0;
return (void*)nlp;
}
/*---------------------------------------------------------------------------*\
nlp_destory()
Initialisation function for NLP pitch estimator.
\*---------------------------------------------------------------------------*/
void nlp_destroy(void *nlp_state)
{
assert(nlp_state != NULL);
free(nlp_state);
}
/*---------------------------------------------------------------------------*\
nlp()
Determines the pitch in samples using the Non Linear Pitch (NLP)
algorithm [1]. Returns the fundamental in Hz. Note that the actual
pitch estimate is for the centre of the M sample Sn[] vector, not
the current N sample input vector. This is (I think) a delay of 2.5
frames with N=80 samples. You should align further analysis using
this pitch estimate to be centred on the middle of Sn[].
Two post processors have been tried, the MBE version (as discussed
in [1]), and a post processor that checks sub-multiples. Both
suffer occasional gross pitch errors (i.e. neither are perfect). In
the presence of background noise the sub-multiple algorithm tends
towards low F0 which leads to better sounding background noise than
the MBE post processor.
A good way to test and develop the NLP pitch estimator is using the
tnlp (codec2/unittest) and the codec2/octave/plnlp.m Octave script.
A pitch tracker searching a few frames forward and backward in time
would be a useful addition.
References:
[1] http://www.itr.unisa.edu.au/~steven/thesis/dgr.pdf Chapter 4
\*---------------------------------------------------------------------------*/
float nlp(
void *nlp_state,
float Sn[], /* input speech vector */
int n, /* frames shift (no. new samples in Sn[]) */
int m, /* analysis window size */
int pmin, /* minimum pitch value */
int pmax, /* maximum pitch value */
float *pitch, /* estimated pitch period in samples */
COMP Sw[], /* Freq domain version of Sn[] */
float *prev_Wo
)
{
NLP *nlp;
float notch; /* current notch filter output */
COMP Fw[PE_FFT_SIZE]; /* DFT of squared signal */
float gmax;
int gmax_bin;
int i,j;
float best_f0;
assert(nlp_state != NULL);
nlp = (NLP*)nlp_state;
/* Square, notch filter at DC, and LP filter vector */
for(i=m-n; i<M; i++) /* square latest speech samples */
nlp->sq[i] = Sn[i]*Sn[i];
for(i=m-n; i<m; i++) { /* notch filter at DC */
notch = nlp->sq[i] - nlp->mem_x;
notch += COEFF*nlp->mem_y;
nlp->mem_x = nlp->sq[i];
nlp->mem_y = notch;
nlp->sq[i] = notch;
}
for(i=m-n; i<m; i++) { /* FIR filter vector */
for(j=0; j<NLP_NTAP-1; j++)
nlp->mem_fir[j] = nlp->mem_fir[j+1];
nlp->mem_fir[NLP_NTAP-1] = nlp->sq[i];
nlp->sq[i] = 0.0;
for(j=0; j<NLP_NTAP; j++)
nlp->sq[i] += nlp->mem_fir[j]*nlp_fir[j];
}
/* Decimate and DFT */
for(i=0; i<PE_FFT_SIZE; i++) {
Fw[i].real = 0.0;
Fw[i].imag = 0.0;
}
for(i=0; i<m/DEC; i++) {
Fw[i].real = nlp->sq[i*DEC]*(0.5 - 0.5*cos(2*PI*i/(m/DEC-1)));
}
dump_dec(Fw);
four1(&Fw[-1].imag,PE_FFT_SIZE,1);
for(i=0; i<PE_FFT_SIZE; i++)
Fw[i].real = Fw[i].real*Fw[i].real + Fw[i].imag*Fw[i].imag;
dump_sq(nlp->sq);
dump_Fw(Fw);
/* find global peak */
gmax = 0.0;
gmax_bin = PE_FFT_SIZE*DEC/pmax;
for(i=PE_FFT_SIZE*DEC/pmax; i<=PE_FFT_SIZE*DEC/pmin; i++) {
if (Fw[i].real > gmax) {
gmax = Fw[i].real;
gmax_bin = i;
}
}
best_f0 = post_process_sub_multiples(Fw, pmin, pmax, gmax, gmax_bin,
prev_Wo);
/* Shift samples in buffer to make room for new samples */
for(i=0; i<m-n; i++)
nlp->sq[i] = nlp->sq[i+n];
/* return pitch and F0 estimate */
*pitch = (float)SAMPLE_RATE/best_f0;
return(best_f0);
}
/*---------------------------------------------------------------------------*\
post_process_sub_multiples()
Given the global maximma of Fw[] we search interger submultiples for
local maxima. If local maxima exist and they are above an
experimentally derived threshold (OK a magic number I pulled out of
the air) we choose the submultiple as the F0 estimate.
The rational for this is that the lowest frequency peak of Fw[]
should be F0, as Fw[] can be considered the autocorrelation function
of Sw[] (the speech spectrum). However sometimes due to phase
effects the lowest frequency maxima may not be the global maxima.
This works OK in practice and favours low F0 values in the presence
of background noise which means the sinusoidal codec does an OK job
of synthesising the background noise. High F0 in background noise
tends to sound more periodic introducing annoying artifacts.
\*---------------------------------------------------------------------------*/
float post_process_sub_multiples(COMP Fw[],
int pmin, int pmax, float gmax, int gmax_bin,
float *prev_Wo)
{
int min_bin, cmax_bin;
int mult;
float thresh, best_f0;
int b, bmin, bmax, lmax_bin;
float lmax, cmax;
int prev_f0_bin;
/* post process estimate by searching submultiples */
mult = 2;
min_bin = PE_FFT_SIZE*DEC/pmax;
cmax_bin = gmax_bin;
prev_f0_bin = *prev_Wo*(4000.0/PI)*(PE_FFT_SIZE*DEC)/SAMPLE_RATE;
while(gmax_bin/mult >= min_bin) {
b = gmax_bin/mult; /* determine search interval */
bmin = 0.8*b;
bmax = 1.2*b;
if (bmin < min_bin)
bmin = min_bin;
/* lower threshold to favour previous frames pitch estimate,
this is a form of pitch tracking */
if ((prev_f0_bin > bmin) && (prev_f0_bin < bmax))
thresh = CNLP*0.5*gmax;
else
thresh = CNLP*gmax;
lmax = 0;
lmax_bin = bmin;
for (b=bmin; b<=bmax; b++) /* look for maximum in interval */
if (Fw[b].real > lmax) {
lmax = Fw[b].real;
lmax_bin = b;
}
if (lmax > thresh)
if ((lmax > Fw[lmax_bin-1].real) && (lmax > Fw[lmax_bin+1].real)) {
cmax = lmax;
cmax_bin = lmax_bin;
}
mult++;
}
best_f0 = (float)cmax_bin*SAMPLE_RATE/(PE_FFT_SIZE*DEC);
return best_f0;
}
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