mirror of
https://github.com/signalwire/freeswitch.git
synced 2025-08-13 01:26:58 +00:00
git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@125 d0543943-73ff-0310-b7d9-9358b9ac24b2
This commit is contained in:
Michael Jerris
144
libs/codec/lpc10/preemp.c
Normal file
144
libs/codec/lpc10/preemp.c
Normal file
@@ -0,0 +1,144 @@
|
||||
/*
|
||||
|
||||
$Log$
|
||||
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_ */
|
||||
|
||||
Reference in New Issue
Block a user