fir-lib.c

Reference Implementation of G.711 standard and other voice codecs

/*                                                          v2.3 - 03/Dec/2004
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                    ITU-T - USER'S GROUP ON SOFTWARE TOOLS
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MODULE:         FIRFLT, HIGH QUALITY FIR UP/DOWN-SAMPLING FILTER
                Sub-unit: Basic FIR filtering routines

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 FIR up-/down-sampling 
	filtering, independently of filter characteristics initialized by
	functions present in other sub-units of this module.

FUNCTIONS:
  Global (have prototype in firflt.h)
         = hq_kernel(...)        :  FIR-filter function
         = hq_reset(...)         :  clear state variables
                                    (needed only if another signal should
                                    be processed with the same filter)
         = hq_free(...)          :  deallocate FIR-filter memory

  Local (Used by other sub-units of this module, should not be needed by 
         the user's program. Prototypes here and in the sub-units that use 
	 it, but not in firflt.h)
         = fir_initialization(...) : common initialization function for
                                   all filter types;
  Local (should be used only here -- prototypes only in this file)
         = fir_upsampling_kernel(...) : kernel function for all FIR
                                   up-sampling procedures;
         = fir_downsampling_kernel(...) : kernel function for all FIR
                                   down-sampling procedures;

HISTORY:
    16.Dec.91 v0.1 First beta-version <[e-mail]>
    28.Feb.92 v1.0 Release of 1st version to UGST <[e-mail]>
    20.Apr.94 v2.0 Added new filtering routines: modified IRS at 16kHz and
                   48kHz, Delta-SM, Linear-phase band-pass.
                   <[e-mail]>
    30.Sep.94 v2.1 Updated to accomodate changes in the name of the name and
                   slitting of module in several files, for ease of expansion.
    22.Feb.96 v2.2 Changed inclusion of stdlib.h to inconditional, as
                   suggested by Kirchherr (FI/DBP Telekom) to run under
				   OpenVMS/AXP <[e-mail]>
    03.Dec.04 v2.3 Added correction in fir_downsampling_kernel() for sample-based 
				   operation.	<Cyril Guillaum