ivfilt.f,v

lpc10-15为美军2400bps语音压缩标准的C语音源代码。

head	1.3;
access;
symbols;
locks; strict;
comment	@* @;


1.3
date	96.03.15.21.36.29;	author jaf;	state Exp;
branches;
next	1.2;

1.2
date	96.03.13.00.01.00;	author jaf;	state Exp;
branches;
next	1.1;

1.1
date	96.02.07.14.47.34;	author jaf;	state Exp;
branches;
next	;


desc
@@


1.3
log
@Just added a few comments about which array indices of the arguments
are used, and mentioning that this subroutine has no local state.
@
text
@**********************************************************************
*
*	IVFILT Version 48
*
* $Log: ivfilt.f,v $
* Revision 1.2  1996/03/13  00:01:00  jaf
* Comments added explaining that none of the local variables of this
* subroutine need to be saved from one invocation to the next.
*
* Revision 1.1  1996/02/07 14:47:34  jaf
* Initial revision
*
*
**********************************************************************
*
*   2nd order inverse filter, speech is decimated 4:1
*
* Input:
*  LEN    - Length of speech buffers
*  NSAMP  - Number of samples to filter
*  LPBUF  - Low pass filtered speech buffer
*           Indices LEN-NSAMP-7 through LEN read.
* Output:
*  IVBUF  - Inverse filtered speech buffer
*           Indices LEN-NSAMP+1 through LEN written.
*  IVRC   - Inverse filter reflection coefficients (for voicing)
*           Indices 1 and 2 both written (also read, but only after writing).
*
* This subroutine has no local state.
*
	SUBROUTINE IVFILT( LPBUF, IVBUF, LEN, NSAMP, IVRC )

*	Arguments

	INTEGER LEN, NSAMP
	REAL LPBUF(LEN), IVBUF(LEN)
	REAL IVRC(2)

*       Local variables that need not be saved

	INTEGER I, J, K
	REAL R(3), PC1, PC2

*       Local state

*       None

*  Calculate Autocorrelations

	DO I = 1,3
	   R(I) = 0.
	   K = 4*(I-1)
	   DO J = I*4+LEN-NSAMP,LEN,2
	      R(I) = R(I) + LPBUF(J)*LPBUF(J-K)
	   END DO
	END DO

*  Calculate predictor coefficients

	PC1 = 0.
	PC2 = 0.
	IVRC(1) = 0.
	IVRC(2) = 0.
	IF (R(1) .GT. 1.0E-10) THEN
	   IVRC(1) = R(2)/R(1)
	   IVRC(2) = (R(3)-IVRC(1)*R(2)) / (R(1)-IVRC(1)*R(2))
	   PC1 = IVRC(1) - IVRC(1)*IVRC(2)
	   PC2 = IVRC(2)
	END IF

*  Inverse filter LPBUF into IVBUF

	DO I = LEN+1-NSAMP,LEN
	   IVBUF(I) = LPBUF(I) - PC1*LPBUF(I-4) - PC2*LPBUF(I-8)
	END DO

	RETURN
	END
@


1.2
log
@Comments added explaining that none of the local variables of this
subroutine need to be saved from one invocation to the next.
@
text
@d6 4
d18 1
a18 1
* Inputs:
d22 1
d25 1
d27 3
d32 3
d39 1
a39 4
*       Local variables
*       
*       None of these need to have their values saved from one
*       invocation to the next.
d43 4
@


1.1
log
@Initial revision
@
text
@d5 4
a8 1
* $Log$
d23 11
a33 3
	INTEGER LEN, NSAMP, I, J, K
	REAL IVBUF(LEN), LPBUF(LEN)
	REAL R(3), PC1, PC2, IVRC(2)
@