134 lines
3.8 KiB
C
134 lines
3.8 KiB
C
/*
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$Log: preemp.c,v $
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Revision 1.1 2004/05/04 11:16:43 csoutheren
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Initial version
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Revision 1.1 2000/06/05 04:45:12 robertj
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Added LPC-10 2400bps codec
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* Revision 1.1 1996/08/19 22:30:58 jaf
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* Initial revision
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*
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*/
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#ifdef P_R_O_T_O_T_Y_P_E_S
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extern int preemp_(real *inbuf, real *pebuf, integer *nsamp, real *coef, real *z__);
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#endif
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/* -- translated by f2c (version 19951025).
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You must link the resulting object file with the libraries:
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-lf2c -lm (in that order)
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*/
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#include "f2c.h"
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/* ******************************************************************* */
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/* PREEMP Version 55 */
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/* $Log: preemp.c,v $
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* Revision 1.1 2004/05/04 11:16:43 csoutheren
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* Initial version
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*
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* Revision 1.1 2000/06/05 04:45:12 robertj
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* Added LPC-10 2400bps codec
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*
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* Revision 1.1 1996/08/19 22:30:58 jaf
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* Initial revision
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*
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*/
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/* Revision 1.3 1996/03/14 23:16:29 jaf */
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/* Just added a few comments about which array indices of the arguments */
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/* are used, and mentioning that this subroutine has no local state. */
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/* Revision 1.2 1996/03/11 23:23:34 jaf */
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/* Added a bunch of comments to an otherwise simple subroutine. */
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/* Revision 1.1 1996/02/07 14:48:48 jaf */
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/* Initial revision */
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/* ******************************************************************* */
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/* Preemphasize speech with a single-zero filter. */
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/* (When coef = .9375, preemphasis is as in LPC43.) */
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/* Inputs: */
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/* NSAMP - Number of samples to filter */
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/* INBUF - Input speech buffer */
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/* Indices 1 through NSAMP are read. */
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/* COEF - Preemphasis coefficient */
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/* Input/Output: */
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/* Z - Filter state */
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/* Output: */
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/* PEBUF - Preemphasized speech buffer (can be equal to INBUF) */
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/* Indices 1 through NSAMP are modified. */
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/* This subroutine has no local state. */
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/* Subroutine */ int preemp_(real *inbuf, real *pebuf, integer *nsamp, real *
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coef, real *z__)
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{
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/* System generated locals */
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integer i__1;
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/* Local variables */
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real temp;
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integer i__;
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/* Arguments */
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/* Local variables */
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/* None of these need to have their values saved from one */
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/* invocation to the next. */
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/* Logically, this subroutine computes the output sequence */
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/* pebuf(1:nsamp) defined by: */
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/* pebuf(i) = inbuf(i) - coef * inbuf(i-1) */
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/* where inbuf(0) is defined by the value of z given as input to */
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/* this subroutine. */
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/* What is this filter's frequency response and phase response? */
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/* Why is this filter applied to the speech? */
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/* Could it be more efficient to apply multiple filters */
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/* simultaneously, by combining them into one equivalent filter? */
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/* Are there ever cases when "factoring" one high-order filter into
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*/
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/* multiple smaller-order filter actually reduces the number of */
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/* arithmetic operations needed to perform them? */
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/* When I first read this subroutine, I didn't understand why the */
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/* variable temp was used. It seemed that the statements in the do
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*/
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/* loop could be replaced with the following: */
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/* pebuf(i) = inbuf(i) - coef * z */
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/* z = inbuf(i) */
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/* The reason for temp is so that even if pebuf and inbuf are the */
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/* same arrays in memory (i.e., they are aliased), then this */
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/* subroutine will still work correctly. I didn't realize this */
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/* until seeing the comment after PEBUF above that says "(can be */
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/* equal to INBUF)". */
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/* Parameter adjustments */
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--pebuf;
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--inbuf;
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/* Function Body */
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i__1 = *nsamp;
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for (i__ = 1; i__ <= i__1; ++i__) {
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temp = inbuf[i__] - *coef * *z__;
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*z__ = inbuf[i__];
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pebuf[i__] = temp;
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/* L10: */
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}
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return 0;
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} /* preemp_ */
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