lpc10/ivfilt.c

   1 /*
   2
   3  * Revision 1.1  1996/08/19  22:31:53  jaf
   4  * Initial revision
   5  *
   6
   7 */
   8
   9 /*  -- translated by f2c (version 19951025).
  10    You must link the resulting object file with the libraries:
  11         -lf2c -lm   (in that order)
  12 */
  13
  14 #include "f2c.h"
  15
  16 extern int ivfilt_(real *lpbuf, real *ivbuf, integer *len, integer *nsamp, real *ivrc);
  17
  18 /* ********************************************************************* */
  19
  20 /*      IVFILT Version 48 */
  21
  22 /*
  23  * Revision 1.1  1996/08/19  22:31:53  jaf
  24  * Initial revision
  25  * */
  26 /* Revision 1.3  1996/03/15  21:36:29  jaf */
  27 /* Just added a few comments about which array indices of the arguments */
  28 /* are used, and mentioning that this subroutine has no local state. */
  29
  30 /* Revision 1.2  1996/03/13  00:01:00  jaf */
  31 /* Comments added explaining that none of the local variables of this */
  32 /* subroutine need to be saved from one invocation to the next. */
  33
  34 /* Revision 1.1  1996/02/07 14:47:34  jaf */
  35 /* Initial revision */
  36
  37
  38 /* ********************************************************************* */
  39
  40 /*   2nd order inverse filter, speech is decimated 4:1 */
  41
  42 /* Input: */
  43 /*  LEN    - Length of speech buffers */
  44 /*  NSAMP  - Number of samples to filter */
  45 /*  LPBUF  - Low pass filtered speech buffer */
  46 /*           Indices LEN-NSAMP-7 through LEN read. */
  47 /* Output: */
  48 /*  IVBUF  - Inverse filtered speech buffer */
  49 /*           Indices LEN-NSAMP+1 through LEN written. */
  50 /*  IVRC   - Inverse filter reflection coefficients (for voicing) */
  51 /*          Indices 1 and 2 both written (also read, but only after writing).
  52 */
  53
  54 /* This subroutine has no local state. */
  55
  56 /* Subroutine */ int ivfilt_(real *lpbuf, real *ivbuf, integer *len, integer *
  57         nsamp, real *ivrc)
  58 {
  59     /* System generated locals */
  60     integer i__1;
  61
  62     /* Local variables */
  63     integer i__, j, k;
  64     real r__[3], pc1, pc2;
  65
  66 /*      Arguments */
  67 /*       Local variables that need not be saved */
  68 /*       Local state */
  69 /*       None */
  70 /*  Calculate Autocorrelations */
  71     /* Parameter adjustments */
  72     --ivbuf;
  73     --lpbuf;
  74     --ivrc;
  75
  76     /* Function Body */
  77     for (i__ = 1; i__ <= 3; ++i__) {
  78         r__[i__ - 1] = 0.f;
  79         k = (i__ - 1) << 2;
  80         i__1 = *len;
  81         for (j = (i__ << 2) + *len - *nsamp; j <= i__1; j += 2) {
  82             r__[i__ - 1] += lpbuf[j] * lpbuf[j - k];
  83         }
  84     }
  85 /*  Calculate predictor coefficients */
  86     pc1 = 0.f;
  87     pc2 = 0.f;
  88     ivrc[1] = 0.f;
  89     ivrc[2] = 0.f;
  90     if (r__[0] > 1e-10f) {
  91         ivrc[1] = r__[1] / r__[0];
  92         ivrc[2] = (r__[2] - ivrc[1] * r__[1]) / (r__[0] - ivrc[1] * r__[1]);
  93         pc1 = ivrc[1] - ivrc[1] * ivrc[2];
  94         pc2 = ivrc[2];
  95     }
  96 /*  Inverse filter LPBUF into IVBUF */
  97     i__1 = *len;
  98     for (i__ = *len + 1 - *nsamp; i__ <= i__1; ++i__) {
  99         ivbuf[i__] = lpbuf[i__] - pc1 * lpbuf[i__ - 4] - pc2 * lpbuf[i__ - 8];
 100     }
 101     return 0;
 102 } /* ivfilt_ */
 103