refltoauto.3

speech signal process tools

.\" Copyright (c) 1986-1990 Entropic Speech, Inc.
.\" Copyright (c) 1991 Entropic Research Laboratory, Inc. All rights reserved.
.\" @(#)refltoauto.3	1.6 29 Jul 1991 ESI/ERL
.ds ]W (c) 1991 Entropic Research Laboratory, Inc.
.TH REFL_TO_AUTO 3\-ESPSsp 29 Jul 1991
.SH NAME

refl_to_auto \- convert reflection coefficients and prediction filter error to autocorrelation coefficients.
.SH SYNOPSIS
.ft B
refl_to_auto (refl_coeff, pfe, autocorrn, order)
.br
float *refl_coeff, pfe, *autocorrn;
.br
int     order;
.SH DESCRIPTION
.PP
.I refl_to_auto
converts 
.I order 
reflection coefficients 
.I refl_coeff
and the prediction filter error 
.I pfe 
(also called the linear predictive analysis gain or error)
into the equivalent
.I order + 1 
autocorrelation coefficients
.I autocorrn.
For the input, only
.I refl_coeff[1]
to
.I refl_coeff[order]
are processed and
.I refl_coeff[0]
is ignored.  On return
.I autocorrn[1]
to 
.I autocorrn[order+1]
are the desired autocorrelation coefficients and
.I autocorrn[0]
should be ignored.
.SH EXAMPLE
.PP
.nf
/*
 * We want to convert \fIorder\fP reflection coefficients to
 * \fIorder + 1\fP autocorrelation coefficients. Assume the
 * array ref_coeff contains \fIorder\fP reflection coefficients
 * starting from ref_coeff[0] to ref_coeff[order - 1] and the
 * autocorrelation coefficient array auto_corr has enough memory
 * to hold \fIorder + 1\fP coefficients.
 *
 */

	int	order = 3;
	float	ref_coeff[3] = {	/* reflection coefficients */
		 -0.248618, 0.81, 0.0
		};
	float	alpha = 10.0;	/* prediction filter error, AKA alpha */
	float	auto_corr[4];	/* order + 1 array */

	/*
	 * The following statement will convert the order ref_coeff
	 * array to the proper order + 1 auto_corr array.
	 *
	 */

	refl_to_auto (ref_coeff - 1, alpha, auto_corr, order);

	/*
	 * Notice we are sending (ref_coeff - 1) pointer;
	 * it is the one before ref_coeff[0].
	 * Therefore, in the refl_to_auto routine,
	 * refl_coeff[1] will actually be ref_coeff[0].
	 * 
	 */
.fi
.SH REFERENCES
[1] Programs for Digital Signal Processing, edited by the Digital Signal Processing
Committee, IEEE Acoustics, Speech, and Signal Processing Society, Chapter 4.3,
pp 4.3-1 to 4.3-7.
.SH "SEE ALSO"
covar(3\-ESPSsp),  get_atal(3\-ESPSsp),
get_burg(3\-ESPSsp), lar_to_rc(3\-ESPSsp),
refl_to_filter(3\-ESPSsp)
.SH AUTHOR
Code by Ajaipal S. Virdy, manual page by D. Burton and A. Virdy.