delay.m

实现fs1016w的CELP的低速率语音编解码功能的基于vc开发环境的原代码。

% MATLAB SIMULATION OF NSA FS-1016 CELP v3.2
% COPYRIGHT (C) 1995-99 ANDREAS SPANIAS AND TED PAINTER
%
% This Copyright applies only to this particular MATLAB implementation
% of the FS-1016 CELP coder.  The MATLAB software is intended only for educational
% purposes.  No other use is intended or authorized.  This is not a public
% domain program and distribution to individuals or networks is strictly
% prohibited.  Be aware that use of the standard in any form is goverened
% by rules of the US DoD.  Therefore patents and royalties may apply to
% authors, companies, or committees associated with this standard, FS-1016.  For
% questions regarding the MATLAB implementation please contact Andreas
% Spanias at  [phone].  For questions on rules,
% royalties, or patents associated with the standard, please contact the DoD.
%
% ALL DERIVATIVE WORKS MUST INCLUDE THIS COPYRIGHT NOTICE.
%
% ******************************************************************
% DELAY
%
% PORTED TO MATLAB FROM CELP 3.2a C RELEASE
% 7-5-94
%
% ******************************************************************
%
% DESCRIPTION
%
% Time delay a bandlimited signal using point-by-point recursion
%
% DESIGN NOTES
%
% Subroutine to time delay a bandlimited signal by resampling the
% reconstructed data (aka sinc interpolation).  The well known
% reconstruction formula is:
%
%               |    M2      sin[pi(t-nT)/T]    M2
%    y(n) = X(t)| = SUM x(n) --------------- = SUM x(n) sinc[(t-nT)/T]
%               |   n=M1         pi(t-nT)/T    n=M1
%               |t=n+d
%
% The interpolating (sinc) function is Hamming windowed to bandlimit
% the signal to reduce aliasing.
%
% Multiple simultaneous time delays may be efficiently calculated
% by polyphase filtering.  Polyphase filters decimate the unused
% filter coefficients.  See Chapter 6 in C&R for details.
%
% REFERENCES
%
% 1. Crochiere & Rabiner, Multirate Digital Signal Processing,
%    Prentice-Hall 1983, Chapters 2 and 6.
%
% 2. Kroon & Atal, "Pitch Predictors with High Temporal Resolution,"
%    ICASSP '90, S12.6
%
% VARIABLES
%
% INPUTS
%   x          -     Input signal
%   start      -     Beginning of the output sequence
%   n          -     Length of the input sequence
%   d          -     Fractional pitch
%   m          -     Integer pitch
%
% OUTPUTS
%   y          -     Delayed input signal
%   x          -     Input signal with zeroed upper elements
%
% INTERNALS
%   kmin       -     Lower bound on k
%   kmax       -     Upper bound on k
%   i          -     General purpose loop variable
%   index      -     Quantized fractional pitch delay (using dfrac quantiles)
%
% GLOBALS
%   dfrac      -     Quantized fractional delays (5)
%   twelfths   -     Fractional delays for hamming window
%   wsinc      -     Windowed sinc interpolation kernel
%   hwin       -     Hamming window for application to sinc interp. kernel
%   FirstDelay -     First call flag
%   DelaySize  -     Length of interpolation interval, in samples (8)
%   DelayM1    -     Start of interpolation interval (-4)
%   DelayM2    -     End of interpolation interval (3)
%
% CONSTANTS
%   TRUE       -     Boolean state
%   FALSE      -     Boolean state
%   MAXLP      -     Maximum pitch prediction frame size
%   NFRAC      -     Number of fractional delays (5)
%
% ******************************************************************

function [ x, y ] = delay( x, start, n, d, m )

% DECLARE GLOBAL VARIABLES
global dfrac twelfths wsinc hwin FirstDelay DelaySize DelayM1 DelayM2

% DECLARE GLOBAL CONSTANTS
global TRUE FALSE NFRAC MAXLP

% INIT RETURN VECTOR AND LOCAL VARIABLES
y = zeros( MAXLP, 1 );
kmin = DelayM1;
kmax = kmin + DelaySize - 1;

% GENERATE HAMMING WINDOWED SINC INTERPOLATING FUNCTION FOR EACH
% ALLOWABLE FRACTION.  THE INTERPOLATING FUNCTIONS ARE STORED IN
% TIME REVERSE ORDER (I.E., DELAY APPEARS AS ADVANCE) TO ALIGN
% WITH THE ADAPTIVE CODE BOOK V0 ARRAY.  THE INTERP FILTERS ARE:
%   WSINC(.,0)  FRAC = 1/4 (3/12)
%   WSINC(.,1)  FRAC = 1/3 (4/12)
%   .    .
%   WSINC(.,4)  FRAC = 3/4 (9/12)
if FirstDelay == TRUE
    hwin = ham( (12*DelaySize) + 1 );
    for i = 1:NFRAC
        wsinc( 1:DelaySize, i ) = sinc( dfrac(i) + (kmin:kmax) ) .* ...
                                  hwin( 12*(0:DelaySize-1) + twelfths(i) + 1 );
    end
    FirstDelay = FALSE;
end

% QUANTIZE FRACTIONAL PITCH
index = qd(d);

% RESAMPLE
for i = 0:n-1
    x( start + i ) = sum( x( start - m + i + (kmin:kmax) ) .* ...
                          wsinc((1:DelaySize),index) );
end

% THE V0 ARRAY IN PSEARCH AND PGAIN MUST BE ZERO ABOVE START BECAUSE
% OF OVERLAP AND ADD CONVOLUTION TEHNIQUES USED IN PGAIN
y( 1:n ) = x( start:start+n-1 );
x( start:start+n-1 ) = zeros( n, 1 );