ref: f9d8423d5bb3abb3e62b8545ea21e4feb2641def
dir: /nok_pitch.c/
/**************************************************************************
This software module was originally developed by
Nokia in the course of development of the MPEG-2 AAC/MPEG-4
Audio standard ISO/IEC13818-7, 14496-1, 2 and 3.
This software module is an implementation of a part
of one or more MPEG-2 AAC/MPEG-4 Audio tools as specified by the
MPEG-2 aac/MPEG-4 Audio standard. ISO/IEC gives users of the
MPEG-2aac/MPEG-4 Audio standards free license to this software module
or modifications thereof for use in hardware or software products
claiming conformance to the MPEG-2 aac/MPEG-4 Audio standards. Those
intending to use this software module in hardware or software products
are advised that this use may infringe existing patents. The original
developer of this software module, the subsequent
editors and their companies, and ISO/IEC have no liability for use of
this software module or modifications thereof in an
implementation. Copyright is not released for non MPEG-2 aac/MPEG-4
Audio conforming products. The original developer retains full right to
use the code for the developer's own purpose, assign or donate the code to a
third party and to inhibit third party from using the code for non
MPEG-2 aac/MPEG-4 Audio conforming products. This copyright notice
must be included in all copies or derivative works.
Copyright (c)1997.
***************************************************************************/
/**************************************************************************
nok_pitch.c - Long Term Prediction (LTP) subroutines.
Author(s): Juha Ojanpera, Lin Yin
Nokia Research Center, Speech and Audio Systems.
*************************************************************************/
/**************************************************************************
Version Control Information Method: CVS
Identifiers:
$Revision: 1.7 $
$Date: 2000/02/28 12:18:36 $ (check in)
$Author: lenox $
*************************************************************************/
/**************************************************************************
External Objects Needed
*************************************************************************/
/*
Standard library declarations. */
#include <math.h>
#include <stdio.h>
/*
Interface to related modules. */
#include "tf_main.h"
#include "block.h"
#include "interface.h"
#include "nok_ltp_common.h"
#include "nok_ltp_enc.h"
/*************************************************************************
External Objects Provided
*************************************************************************/
#include "nok_pitch.h"
/**************************************************************************
Internal Objects
*************************************************************************/
#include "nok_ltp_common_internal.h"
void lnqgj (double (*a)[LPC + 1]);
void w_quantize (double *freq, int *ltp_idx);
/*
Purpose: Codebook for LTP weight coefficients. */
double codebook[CODESIZE] =
{
0.570829,
0.696616,
0.813004,
0.911304,
0.984900,
1.067894,
1.194601,
1.369533
};
/**************************************************************************
Title: snr_pred
Purpose: Determines is it feasible to employ long term prediction in
the encoder.
Usage: y = snr_pred(mdct_in, mdct_pred, sfb_flag, sfb_offset,
block_type, side_info, num_of_sfb)
Input: mdct_in - spectral coefficients
mdct_pred - predicted spectral coefficients
sfb_flag - an array of flags indicating whether LTP is
switched on (1) /off (0). One bit is reseved
for each sfb.
sfb_offset - scalefactor boundaries
block_type - window sequence type
side_info - LTP side information
num_of_sfb - number of scalefactor bands
Output: y - number of bits saved by using long term prediction
References: -
Explanation: -
Author(s): Juha Ojanpera, Lin Yin
*************************************************************************/
double
snr_pred (double *mdct_in,
double *mdct_pred,
int *sfb_flag,
int *sfb_offset,
enum WINDOW_TYPE block_type,
int side_info,
int num_of_sfb
)
{
int i, j, flen;
double snr_limit;
double num_bit, snr[NSFB_LONG];
double temp1, temp2;
double energy[BLOCK_LEN_LONG], snr_p[BLOCK_LEN_LONG];
if (block_type != ONLY_SHORT_WINDOW)
{
flen = BLOCK_LEN_LONG;
snr_limit = 1.e-30;
}
else
{
flen = BLOCK_LEN_SHORT;
snr_limit = 1.e-20;
}
for (i = 0; i < flen; i++)
{
energy[i] = mdct_in[i] * mdct_in[i];
snr_p[i] = (mdct_in[i] - mdct_pred[i]) * (mdct_in[i] - mdct_pred[i]);
}
num_bit = 0.0;
for (i = 0; i < num_of_sfb; i++)
{
temp1 = 0.0;
temp2 = 0.0;
for (j = sfb_offset[i]; j < sfb_offset[i + 1]; j++)
{
temp1 += energy[j];
temp2 += snr_p[j];
}
if (temp2 < snr_limit)
temp2 = snr_limit;
if (temp1 > /*1.e-20*/0.0)
snr[i] = -10. * log10 (temp2 / temp1);
else
snr[i] = 0.0;
sfb_flag[i] = 1;
if (block_type != ONLY_SHORT_WINDOW)
{
if (snr[i] <= 0.0)
{
sfb_flag[i] = 0;
for (j = sfb_offset[i]; j < sfb_offset[i + 1]; j++)
mdct_pred[j] = 0.0;
} else {
num_bit += snr[i] / 6. * (sfb_offset[i + 1] - sfb_offset[i]);
}
}
}
if (num_bit < side_info)
{
num_bit = 0.0;
for (j = 0; j < flen; j++)
mdct_pred[j] = 0.0;
for (i = 0; i < num_of_sfb; i++)
sfb_flag[i] = 0;
}
else
num_bit -= side_info;
return (num_bit);
}
/**************************************************************************
Title: prediction
Purpose: Predicts current frame from the past output samples.
Usage: prediction(buffer, predicted_samples, weight, delay, flen)
Input: buffer - past reconstructed output samples
weight - LTP gain (scaling factor)
delay - LTP lag (optimal delay)
flen - length of the frame
Output: predicted_samples - predicted samples
References: -
Explanation: -
Author(s): Juha Ojanpera, Lin Yin
*************************************************************************/
void
prediction (short *buffer,
double *predicted_samples,
double *weight,
int delay,
int flen
)
{
int i, j;
int offset;
for (i = 0; i < flen; i++)
{
offset = NOK_LT_BLEN - flen - delay + i - (LPC - 1) / 2;
predicted_samples[i] = 0.0;
for (j = 0; j < LPC; j++)
predicted_samples[i] += weight[j] * buffer[offset + j];
}
}
/**************************************************************************
Title: estimate_delay
Purpose: Estimates optimal delay between current frame and past
reconstructed output samples. The lag between 0...DELAY-1
with the maximum correlation becomes the LTP lag (or delay).
Usage: y = estimate_delay(sb_samples, x_buffer, flen)
Input: sb_samples - current frame
x_buffer - past reconstructed output samples
flen - length of the frame
Output: y - LTP lag
References: -
Explanation: -
Author(s): Juha Ojanpera, Lin Yin
*************************************************************************/
int estimate_delay (double *sb_samples,
short *x_buffer
// ,int flen
)
{
int i, j;
int delay;
double corr[DELAY],corrtmp;
double p_max, energy;
p_max = 0.0;
delay = 0;
energy = 0.0;
corr[0] = 0.0;
for (j = 1; j < 2049; j++)
{
corr[0] += x_buffer[NOK_LT_BLEN - j] * sb_samples[2048 - j];
energy += x_buffer[NOK_LT_BLEN - j] * x_buffer[NOK_LT_BLEN - j];
}
corrtmp=corr[0];
if (energy != 0.0)
corr[0] = corr[0] / sqrt(energy);
else
corr[0] = 0.0;
if (p_max < corr[0])
{
p_max = corr[0];
delay = 0;
}
/* Used to look like this:
for (i = 1; i < DELAY; i+=16)
Because the new code by Oxygene2000 is so fast, we can now look for the
delay in steps of 1, instead of 16. Thus giving a more accurate delay estimation
*/
for (i = 1; i < DELAY; i++)
{
//NOK_LT_BLEN=4096
energy -= x_buffer[NOK_LT_BLEN - i] * x_buffer[NOK_LT_BLEN - i];
energy += x_buffer[NOK_LT_BLEN - i - 2048] * x_buffer[NOK_LT_BLEN - i - 2048]; //2048=j_max
corr[i] = corrtmp;
corr[i] -= x_buffer[NOK_LT_BLEN - i] * sb_samples[2047];
corr[i] += x_buffer[NOK_LT_BLEN - i - 2048] * sb_samples[0];
corrtmp=corr[i];
//flen=2048
// for (j = 1; j < 2049; j++) //2049=flen+1
// {
// corr[i] += x_buffer[NOK_LT_BLEN - i - j] * sb_samples[2048 - j];
// energy += x_buffer[NOK_LT_BLEN - i - j] * x_buffer[NOK_LT_BLEN - i - j];
// }
if (energy != 0.0)
corr[i] = corr[i] / sqrt(energy);
else
corr[i] = 0.0;
if (p_max < corr[i])
{
p_max = corr[i];
delay = i;
}
}
// if (delay < (LPC - 1) / 2)
// delay = (LPC - 1) / 2;
if (delay<0) delay=0; //for LPC=1
/*
fprintf(stdout, "delay : %d ... ", delay);
*/
return delay;
}
/**************************************************************************
Title: pitch
Purpose: Calculates LTP gains, quantizes them and finally scales
the past output samples (from 'delay' to 'delay'+'flen')
to get the predicted frame.
Usage: pitch(sb_samples, sb_samples_pred, x_buffer, ltp_coef,
delay, flen)
Input: sb_samples - current frame
x_buffer - past reconstructed output samples
delay - LTP lag
flen - length of the frame
Output: sb_samples_pred - predicted frame
ltp_coef - indices of the LTP gains
References: 1.) lnqgj
2.) w_quantize
3.) prediction
Explanation: -
Author(s): Juha Ojanpera, Lin Yin
*************************************************************************/
void
pitch (double *sb_samples,
double *sb_samples_pred,
short *x_buffer,
int *ltp_coef,
int delay,
int flen
)
{
int i, k, j;
int offset1, offset2;
double weight[LPC];
double r[LPC][LPC + 1];
for (i = 0; i < LPC; i++)
for (j = 0; j < LPC; j++)
{
offset1 = NOK_LT_BLEN - flen - delay + i - (LPC - 1) / 2;
offset2 = NOK_LT_BLEN - flen - delay + j - (LPC - 1) / 2;
r[i][j] = 0.0;
for (k = 0; k < flen; k++)
r[i][j] += x_buffer[offset1 + k] * x_buffer[offset2 + k];
}
for (i = 0; i < LPC; i++)
r[i][i] = 1.010 * r[i][i];
for (i = 0; i < LPC; i++)
{
offset1 = NOK_LT_BLEN - flen - delay + i - (LPC - 1) / 2;
r[i][LPC] = 0.0;
for (k = 0; k < flen; k++)
r[i][LPC] += x_buffer[offset1 + k] * sb_samples[k];
}
for (i = 0; i < LPC; i++)
weight[i] = 0.0;
if (r[(LPC - 1) / 2][(LPC - 1) / 2] != 0.0)
weight[(LPC - 1) / 2] = r[(LPC - 1) / 2][LPC] / r[(LPC - 1) / 2][(LPC - 1) / 2];
lnqgj (r);
for (i = 0; i < LPC; i++)
weight[i] = r[i][LPC];
/*
fprintf(stdout, "unquantized weight : %f ... ", weight[0]);
*/
w_quantize (weight, ltp_coef);
/*
fprintf(stdout, "quantized weight : %f\n", weight[0]);
*/
prediction (x_buffer, sb_samples_pred, weight, delay, flen);
}
/**************************************************************************
Title: lnqgj
Purpose: Calculates LTP gains.
Usage: lnqgj(a)
Input: a - auto-correlation matrix
Output: a - LTP gains (in the last column)
References: -
Explanation: -
Author(s): Juha Ojanpera, Lin Yin
*************************************************************************/
void
lnqgj (double (*a)[LPC + 1])
{
int nn, nnpls1, ip, i, j;
double p, w;
for (nn = 0; nn < LPC; nn++)
{
p = 0.0;
nnpls1 = nn + 1;
for (i = nn; i < LPC; i++)
if (p - fabs (a[i][nn]) < 0)
{
p = fabs (a[i][nn]);
ip = i;
}
if (p - 1.e-10 <= 0)
return;
if (p - 1.e-10 > 0)
{
for (j = nn; j <= LPC; j++)
{
w = a[nn][j];
a[nn][j] = a[ip][j];
a[ip][j] = w;
}
for (j = nnpls1; j <= LPC; j++)
a[nn][j] = a[nn][j] / a[nn][nn];
for (i = 0; i < LPC; i++)
if ((i - nn) != 0)
for (j = nnpls1; j <= LPC; j++)
a[i][j] = a[i][j] - a[i][nn] * a[nn][j];
}
}
}
/**************************************************************************
Title: w_quantize
Purpose: Quantizes LTP gain(s).
Usage: w_quantize(freq, ltp_idx)
Input: freq - original LTP gain(s)
Output: freq - LTP gain(s) selected from the codebook
ltp_idx - corresponding indices of the LTP gain(s)
References: -
Explanation: The closest value from the codebook is selected to be the
quantized LTP gain.
Author(s): Juha Ojanpera, Lin Yin
*************************************************************************/
void
w_quantize (double *freq, int *ltp_idx)
{
int i, j;
double dist, low;
low = 1.0e+10;
for (i = 0; i < LPC; i++)
{
// dist = 0.0;
for (j = 0; j < CODESIZE; j++)
{
dist = (freq[i] - codebook[j]) * (freq[i] - codebook[j]);
if (dist < low)
{
low = dist;
ltp_idx[i] = j;
}
}
}
for (j = 0; j < LPC; j++)
freq[j] = codebook[ltp_idx[j]];
}