fir-irs.c

Reference Implementation of G.711 standard and other voice codecs

/*                                                             v3.2 22.Dec.2004
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                   ========================================
                    ITU-T - USER'S GROUP ON SOFTWARE TOOLS
                   ========================================

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       COPYRIGHT NOTE: This source code, and all of its derivations,
       is subject to the "ITU-T General Public License". Please have
       it  read  in    the  distribution  disk,   or  in  the  ITU-T
       Recommendation G.191 on "SOFTWARE TOOLS FOR SPEECH AND  AUDIO
       CODING STANDARDS".
       =============================================================

MODULE:         FIRFLT, HIGH QUALITY FIR UP/DOWN-SAMPLING FILTER
                Sub-unit: IRS filtering

ORIGINAL BY:
                Rudolf Hofmann
                Advanced Development Digital Signal Processing
                PHILIPS KOMMUNIKATIONS INDUSTRIE AG
                Kommunikationssysteme
                Thurn-und-Taxis-Strasse 14
                D-8500 Nuernberg 10 (Germany)

                Phone : [phone]
                FAX   : [phone]
                EMail : [e-mail]

DESCRIPTION:
        This file contains procedures for IRS send part filtering for
	several sampling rates. Up and down sampling has not been made 
	part of this sub-unit.

FUNCTIONS:
  Global (have prototype in firflt.h)
         = irs_8khz_init()       :  initialize IRS weighting filter  8 kHz
         = irs_16khz_init()      :  initialize IRS weighting filter 16 kHz
         = mod_irs_16khz_init()
         = mod_irs_48khz_init()

  Local (should be used only here -- prototypes only in this file)
         = fill_irs8khz(...)     : idem, for IRS @  8 kHz
         = fill_irs16khz(...)    : idem, for IRS @ 16 kHz
         = fill_modified_irs16khz(...): idem, for mod.IRS @ 16kHz
         = fill_modified_irs48khz(...): idem, for mod.IRS @ 48kHz



HISTORY:
  16.Dec.1991 v0.1 First beta-version <[e-mail]>
  28.Feb.1992 v1.0 Release of 1st version to UGST <[e-mail]>
  20.Apr.1994 v2.0 Added new filtering routines: modified IRS at 16kHz and
                   48kHz, Delta-SM, Linear-phase band-pass.
                   <[e-mail]>
  30.Sep.1994 v2.1 Updated to accomodate changes in the name of the name and
                   slitting of module in several files, for ease of expansion.
		    <[e-mail]>
  18.Nov.1996 v2.2 Modified gain in modified IRS initialization functions   
                   mod_irs_{48,16}k_init() from 1.0 to -1.0 to fix phase
		   inversion characteristic. <[e-mail]>
  02.Jul.1999 v3.0 Added modified IRS filter RECEIVE-side characteristic 
                   for 8 and 16 kHz sampling-rate, as 1:1 filters. <simao>
  13.Mar.2000 v3.1 Replaced coefficients for modified IRS receive 
                   characteristics to get a closer match to the mask
                   <simao>.
  22.Dec.2004 v3.2 The modified IRS send-side filter (48kHz) is made symmetric. <Cyril Guillaum