codecs/lpc10/preemp.c

   1 /*
   2
   3 $Log$
   4 Revision 1.15  2004/06/26 03:50:14  markster
   5 Merge source cleanups (bug #1911)
   6
   7 Revision 1.14  2003/02/12 13:59:15  matteo
   8 mer feb 12 14:56:57 CET 2003
   9
  10 Revision 1.1.1.1  2003/02/12 13:59:15  matteo
  11 mer feb 12 14:56:57 CET 2003
  12
  13 Revision 1.2  2000/01/05 08:20:39  markster
  14 Some 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
  30 extern 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_ */
 144