computerc.3t

speech signal process tools

.\" Copyright (c) 1991 Entropic Research Laboratory, Inc.; All rights reserved
.\" @(#)computerc.3t	1.2 06 May 1997 ERL
.ds ]W (c) 1991 Entropic Research Laboratory, Inc.
.TH  COMPUTE_RC 3\-ESPSsp 06 May 1997
.SH NAME

.nf
compute_rc \- compute reflection coefficients by various methods
.fi
.SH SYNOPSIS
.nf
.ft B
 
#include <stdio.h>
#include <esps/esps.h>
#include <esps/window.h>
#include <esps/ana_methods.h>

extern int debug_level;

compute_rc(sdata, sdata_size, method, dcrem, win_type, order, 
		  sincn, sc_iter, sc_conv, rc, r, gain)
float  *sdata;
int    sdata_size;
int    method;
int    dcrem;
int    win_type;
int    order;
int    sincn;
int    sc_iter;
double sc_conv;
float  *rc;
double  *r;
float  *gain;

.ft
.fi
.SH DESCRIPTION
.PP
\fIcompute_rc\fP is a "cover function" for various ESPS functions that
compute reflection coefficients.  The method used is determined 
by \fImethod\fP as follows:  
.nf

.TS
center, box, tab(;);
c | c | c
l | l | l
l | l | l.
\fImethod\fP;Description;ESPSsp Functions Used
=
AM_AUTOC;Autocorrelation Method;\fIget_auto\fP(), \fIget_atal\fP()
AM_COV;Covariance Method;\fIget_auto\fP(), \fIcovar\fP()
AM_BURG;Burg Algorithm;\fIget_burg\fP(...'b')
AM_MBURG;Modified Burg Algorithm;\fIget_burg\fP(...'m')
AM_FBURG;Fast Modified Burg Algorithm;\fIget_fburg\fP()
AM_VBURG;Vector Burg Algorithm;\fIget_vburg\fP()
AM_STRCOV;Structured Covariance;\fIstrcov_auto\fP(...'f'...), \fIget_atal\fP()
AM_STRCOV1;Structured Covariance alternate;\fIstrcov_auto\fP(...'w'...), \fIget_atal\fP()
.TE

.fi
.PP
Note that the symbolic constants in the first column can be used 
in the call provided that <esps/ana_methods.h> is included in the 
calling program.  
.PP
All of the methods process \fIsdata_size\fP points of input sampled
data \fIsdata\fP and produce \fIorder\fP reflection coefficients
\fIrc\fP[1] to \fIrc\fP[\fIorder\fP]. The space for \fIrc\fP must be
allocated by the calling program (\fIorder\fP+1 floats).  The methods
also compute the first normalized autocorrelation coefficient
\fIr\fP[0] and the lpc filter gain *\fIgain\fP.  Some of the methods
also compute \fIorder\fP normalized autocorrelation coefficients
reflection coefficients \fIr\fP[1] to \fIr\fP[\fIorder\fP], in which
case sufficient space (\fIorder\fP+1 floats) must be allocated by the
calling program.
.PP
If \fIdcrem\fP != 0, the DC component of \fIsdata\fP will be removed
before analysis (this is done on a copy, in case \fIsdata\fP is used
again in the calling program).  The data (after after DC removal) will
also be windowed using the window specified by \fIwin_type\fP.  The
current available values are WT_NONE, WT_RECT, WT_HAMMING, WT_TRIANG,
WT_HANNING, and WT_COS4.  These symbolic values can be used provided
that <esps/window.h> is included (see \fIwindow\fP (3\-\s-1ESPS\s+1sp).  
.PP
The methods AM_AUTOC, AM_STRCOV, and AM_STRCOV1 operate by estimating
the autocorrelation function and then transforming to reflection
coefficients.  In these cases, if \fIsincn\fP != 0, \fIcompute_rc\fP
will multiply the autocorrelation function by a
\fIsin\fP(\fIx/sincn\fP) function prior to computing the reflection
coefficients.  This has the effect of reducing the spectral resolution
if the spectrum of these coefficients is plotted.
.PP
For the AM_STRCOV method (not including AM_STRCOV1), the estimator
terminates after \fImax_iter\fP iterations, or after the relative
change in autocorrelation values falls below the convergence threshold
\fIconv_test\fR.
.PP
For details about the various functions, see the relevant man pages.  
In some cases, some additional steps are taken by \fIcompute_rc\fP to 
provide uniform interface (e.g., in computing \fIr\fP[0]).  
.PP
\fIcompute_rc\fP does the main computational work in the program 
\fIrefcof\fP(1\-\s-1ESPS\s+1).
.SH EXAMPLES
.PP
.SH ERRORS AND DIAGNOSTICS
.PP
If the external \fIdebug_level\fP is non-zero, various debugging 
messages are printed.  Higher values yield more verbose output.  
.SH FUTURE CHANGES
.PP
.SH BUGS
.PP
None known.
.SH REFERENCES
.PP
.SH "SEE ALSO"
.PP
\fIget_auto\fP (3\-\s-1ESPS\s+1), \fIget_atal\fP (3\-\s-1ESPS\s+1), 
\fIcovar\fP (3\-\s-1ESPS\s+1), \fIget_burg\fP (3\-\s-1ESPS\s+1), 
\fIget_fburg\fP (3\-\s-1ESPS\s+1), \fIget_vburg\fP (3\-\s-1ESPS\s+1),
\fIstrcov_auto\fP (3\-\s-1ESPS\s+1), \fIstruct_cov\fP (3\-\s-1ESPS\s+1),
\fIrefcof\fP (1\-\s-1ESPS\s+1), \fIme_spec\fP (1\-\s-1ESPS\s+1)
.SH AUTHOR
.PP
Program and man page by John Shore