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Diffstat (limited to 'trunk/codecs/lpc10/preemp.c')
| -rw-r--r-- | trunk/codecs/lpc10/preemp.c | 144 |
1 files changed, 144 insertions, 0 deletions
diff --git a/trunk/codecs/lpc10/preemp.c b/trunk/codecs/lpc10/preemp.c new file mode 100644 index 000000000..645428c3c --- /dev/null +++ b/trunk/codecs/lpc10/preemp.c @@ -0,0 +1,144 @@ +/* + +$Log$ +Revision 1.15 2004/06/26 03:50:14 markster +Merge source cleanups (bug #1911) + +Revision 1.14 2003/02/12 13:59:15 matteo +mer feb 12 14:56:57 CET 2003 + +Revision 1.1.1.1 2003/02/12 13:59:15 matteo +mer feb 12 14:56:57 CET 2003 + +Revision 1.2 2000/01/05 08:20:39 markster +Some OSS fixes and a few lpc changes to make it actually work + + * Revision 1.1 1996/08/19 22:30:58 jaf + * Initial revision + * + +*/ + +/* -- translated by f2c (version 19951025). + You must link the resulting object file with the libraries: + -lf2c -lm (in that order) +*/ + +#include "f2c.h" + +#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 + +/* ******************************************************************* */ + +/* PREEMP Version 55 */ + +/* $Log$ + * Revision 1.15 2004/06/26 03:50:14 markster + * Merge source cleanups (bug #1911) + * + * Revision 1.14 2003/02/12 13:59:15 matteo + * mer feb 12 14:56:57 CET 2003 + * + * Revision 1.1.1.1 2003/02/12 13:59:15 matteo + * mer feb 12 14:56:57 CET 2003 + * + * Revision 1.2 2000/01/05 08:20:39 markster + * Some OSS fixes and a few lpc changes to make it actually work + * + * 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_ */ + |