preemp.c

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/*

$Log$
Revision 1.15 2004/06/26 03:50:14 markster
Merge source cleanups (bug #1911)

Revision 1.14 2003/02/12 13:59:15 matteo
mer feb 12 14:56:57 CET 2003

Revision 1.1.1.1 2003/02/12 13:59:15 matteo
mer feb 12 14:56:57 CET 2003

Revision 1.2 2000/01/05 08:20:39 markster
Some OSS fixes and a few lpc changes to make it actually work

 * Revision 1.1 1996/08/19 22:30:58 jaf
 * Initial revision
 *

*/

/* -- translated by f2c (version 19951025).
 You must link the resulting object file with the libraries:
 -lf2c -lm (in that order)
*/

#include "f2c.h"

#ifdef P_R_O_T_O_T_Y_P_E_S
extern int preemp_(real *inbuf, real *pebuf, integer *nsamp, real *coef, real *z__);
#endif

/* ******************************************************************* */

/* PREEMP Version 55 */

/* $Log$
 * Revision 1.15 2004/06/26 03:50:14 markster
 * Merge source cleanups (bug #1911)
 *
 * Revision 1.14 2003/02/12 13:59:15 matteo
 * mer feb 12 14:56:57 CET 2003
 *
 * Revision 1.1.1.1 2003/02/12 13:59:15 matteo
 * mer feb 12 14:56:57 CET 2003
 *
 * Revision 1.2 2000/01/05 08:20:39 markster
 * Some OSS fixes and a few lpc changes to make it actually work
 *
 * Revision 1.1 1996/08/19 22:30:58 jaf
 * Initial revision
 * */
/* Revision 1.3 1996/03/14 23:16:29 jaf */
/* Just added a few comments about which array indices of the arguments */
/* are used, and mentioning that this subroutine has no local state. */

/* Revision 1.2 1996/03/11 23:23:34 jaf */
/* Added a bunch of comments to an otherwise simple subroutine. */

/* Revision 1.1 1996/02/07 14:48:48 jaf */
/* Initial revision */


/* ******************************************************************* */

/* Preemphasize speech with a single-zero filter. */
/* (When coef = .9375, preemphasis is as in LPC43.) */

/* Inputs: */
/* NSAMP - Number of samples to filter */
/* INBUF - Input speech buffer */
/* Indices 1 through NSAMP are read. */
/* COEF - Preemphasis coefficient */
/* Input/Output: */
/* Z - Filter state */
/* Output: */
/* PEBUF - Preemphasized speech buffer (can be equal to INBUF) */
/* Indices 1 through NSAMP are modified. */

/* This subroutine has no local state. */

/* Subroutine */ int preemp_(real *inbuf, real *pebuf, integer *nsamp, real *
 coef, real *z__)
{
 /* System generated locals */
 integer i__1;

 /* Local variables */
 real temp;
 integer i__;

/* Arguments */
/* Local variables */

/* None of these need to have their values saved from one */
/* invocation to the next. */

/* Logically, this subroutine computes the output sequence */
/* pebuf(1:nsamp) defined by: */

/* pebuf(i) = inbuf(i) - coef * inbuf(i-1) */

/* where inbuf(0) is defined by the value of z given as input to */
/* this subroutine. */

/* What is this filter's frequency response and phase response? */

/* Why is this filter applied to the speech? */

/* Could it be more efficient to apply multiple filters */
/* simultaneously, by combining them into one equivalent filter? */

/* Are there ever cases when "factoring" one high-order filter into
*/
/* multiple smaller-order filter actually reduces the number of */
/* arithmetic operations needed to perform them? */
/* When I first read this subroutine, I didn't understand why the */
/* variable temp was used. It seemed that the statements in the do
*/
/* loop could be replaced with the following: */

/* pebuf(i) = inbuf(i) - coef * z */
/* z = inbuf(i) */

/* The reason for temp is so that even if pebuf and inbuf are the */
/* same arrays in memory (i.e., they are aliased), then this */
/* subroutine will still work correctly. I didn't realize this */
/* until seeing the comment after PEBUF above that says "(can be */
/* equal to INBUF)". */
 /* Parameter adjustments */
 --pebuf;
 --inbuf;

 /* Function Body */
 i__1 = *nsamp;
 for (i__ = 1; i__ <= i__1; ++i__) {
 temp = inbuf[i__] - *coef * *z__;
 *z__ = inbuf[i__];
 pebuf[i__] = temp;
/* L10: */
 }
 return 0;
} /* preemp_ */