ref: c770ed0961baf45b0fbc905dfe629f1a4f7ba7c4
dir: /lpc10/preemp.c/
/*
* 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"
extern int preemp_(real *inbuf, real *pebuf, integer *nsamp, real *coef, real *z__);
/* ******************************************************************* */
/* PREEMP Version 55 */
/*
* 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_ */