Asterisk - The Open Source Telephony Project GIT-master-2de1a68
preemp.c
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1/*
2
3$Log$
4Revision 1.15 2004/06/26 03:50:14 markster
5Merge source cleanups (bug #1911)
6
7Revision 1.14 2003/02/12 13:59:15 matteo
8mer feb 12 14:56:57 CET 2003
9
10Revision 1.1.1.1 2003/02/12 13:59:15 matteo
11mer feb 12 14:56:57 CET 2003
12
13Revision 1.2 2000/01/05 08:20:39 markster
14Some OSS fixes and a few lpc changes to make it actually work
15
16 * Revision 1.1 1996/08/19 22:30:58 jaf
17 * Initial revision
18 *
19
20*/
21
22/* -- translated by f2c (version 19951025).
23 You must link the resulting object file with the libraries:
24 -lf2c -lm (in that order)
25*/
26
27#include "f2c.h"
28
29#ifdef P_R_O_T_O_T_Y_P_E_S
30extern int preemp_(real *inbuf, real *pebuf, integer *nsamp, real *coef, real *z__);
31#endif
32
33/* ******************************************************************* */
34
35/* PREEMP Version 55 */
36
37/* $Log$
38 * Revision 1.15 2004/06/26 03:50:14 markster
39 * Merge source cleanups (bug #1911)
40 *
41 * Revision 1.14 2003/02/12 13:59:15 matteo
42 * mer feb 12 14:56:57 CET 2003
43 *
44 * Revision 1.1.1.1 2003/02/12 13:59:15 matteo
45 * mer feb 12 14:56:57 CET 2003
46 *
47 * Revision 1.2 2000/01/05 08:20:39 markster
48 * Some OSS fixes and a few lpc changes to make it actually work
49 *
50 * Revision 1.1 1996/08/19 22:30:58 jaf
51 * Initial revision
52 * */
53/* Revision 1.3 1996/03/14 23:16:29 jaf */
54/* Just added a few comments about which array indices of the arguments */
55/* are used, and mentioning that this subroutine has no local state. */
56
57/* Revision 1.2 1996/03/11 23:23:34 jaf */
58/* Added a bunch of comments to an otherwise simple subroutine. */
59
60/* Revision 1.1 1996/02/07 14:48:48 jaf */
61/* Initial revision */
62
63
64/* ******************************************************************* */
65
66/* Preemphasize speech with a single-zero filter. */
67/* (When coef = .9375, preemphasis is as in LPC43.) */
68
69/* Inputs: */
70/* NSAMP - Number of samples to filter */
71/* INBUF - Input speech buffer */
72/* Indices 1 through NSAMP are read. */
73/* COEF - Preemphasis coefficient */
74/* Input/Output: */
75/* Z - Filter state */
76/* Output: */
77/* PEBUF - Preemphasized speech buffer (can be equal to INBUF) */
78/* Indices 1 through NSAMP are modified. */
79
80/* This subroutine has no local state. */
81
82/* Subroutine */ int preemp_(real *inbuf, real *pebuf, integer *nsamp, real *
83 coef, real *z__)
84{
85 /* System generated locals */
86 integer i__1;
87
88 /* Local variables */
89 real temp;
90 integer i__;
91
92/* Arguments */
93/* Local variables */
94
95/* None of these need to have their values saved from one */
96/* invocation to the next. */
97
98/* Logically, this subroutine computes the output sequence */
99/* pebuf(1:nsamp) defined by: */
100
101/* pebuf(i) = inbuf(i) - coef * inbuf(i-1) */
102
103/* where inbuf(0) is defined by the value of z given as input to */
104/* this subroutine. */
105
106/* What is this filter's frequency response and phase response? */
107
108/* Why is this filter applied to the speech? */
109
110/* Could it be more efficient to apply multiple filters */
111/* simultaneously, by combining them into one equivalent filter? */
112
113/* Are there ever cases when "factoring" one high-order filter into
114*/
115/* multiple smaller-order filter actually reduces the number of */
116/* arithmetic operations needed to perform them? */
117/* When I first read this subroutine, I didn't understand why the */
118/* variable temp was used. It seemed that the statements in the do
119*/
120/* loop could be replaced with the following: */
121
122/* pebuf(i) = inbuf(i) - coef * z */
123/* z = inbuf(i) */
124
125/* The reason for temp is so that even if pebuf and inbuf are the */
126/* same arrays in memory (i.e., they are aliased), then this */
127/* subroutine will still work correctly. I didn't realize this */
128/* until seeing the comment after PEBUF above that says "(can be */
129/* equal to INBUF)". */
130 /* Parameter adjustments */
131 --pebuf;
132 --inbuf;
133
134 /* Function Body */
135 i__1 = *nsamp;
136 for (i__ = 1; i__ <= i__1; ++i__) {
137 temp = inbuf[i__] - *coef * *z__;
138 *z__ = inbuf[i__];
139 pebuf[i__] = temp;
140/* L10: */
141 }
142 return 0;
143} /* preemp_ */
float real
Definition: lpc10.h:79
INT32 integer
Definition: lpc10.h:80
int preemp_(real *inbuf, real *pebuf, integer *nsamp, real *coef, real *z__)
Definition: preemp.c:82
static int inbuf(struct baseio *bio, FILE *fi)
utility used by inchar(), for base_encode()
Definition: utils.c:590