preemp.c

sloedgy open sip stack source code

/*

$Log: preemp.c,v $
Revision 1.1  2006/06/26 03:02:54  joegenbaclor
I have decided to include the latest development realease  of OPAL tagged Deimos Devel 1 (June 8 2006) as inegrated classes to opensipstack to avoid future version conflicts due to the fast pace in OPAL development.   This move is also aimed to reduce the size of projects using OPAL componets such as the soon to be relased OpenSIPPhone.

Revision 2.2  2005/08/08 03:28:42  dereksmithies
Eradicate all "/ * within comments" messages from GCC compilations.

Revision 2.1  2003/03/14 09:53:27  robertj
Updated to openH323 v1.11.7

Revision 1.1  2000/06/05 04:45:12  robertj
Added LPC-10 2400bps codec

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

*/

#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

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

#include "f2c.h"

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

/* 	PREEMP Version 55 

 * $Log: preemp.c,v $
 * Revision 1.1  2006/06/26 03:02:54  joegenbaclor
 * I have decided to include the latest development realease  of OPAL tagged Deimos Devel 1 (June 8 2006) as inegrated classes to opensipstack to avoid future version conflicts due to the fast pace in OPAL development.   This move is also aimed to reduce the size of projects using OPAL componets such as the soon to be relased OpenSIPPhone.
 *
 * Revision 2.2  2005/08/08 03:28:42  dereksmithies
 * Eradicate all "/ * within comments" messages from GCC compilations.
 *
 * Revision 2.1  2003/03/14 09:53:27  robertj
 * Updated to openH323 v1.11.7
 *
 * Revision 1.1  2000/06/05 04:45:12  robertj
 * Added LPC-10 2400bps codec
 *
 * 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_ */