Waveform Quantization and Compression - Digital Signal Processing: Fundamentals and Applications - page 539

value ¼ sgn(cmp_code)*(512 þ (abs(cmp_code)-96)*32 þ 16);
end
if (abs(cmp_code) > ¼ 112) & (abs(cmp_code)<128)
value ¼ sgn(cmp_code)*(1024 þ (abs(cmp_code)-112)*64 þ 32);
end
Program 11.11. Main program for ADPCM coding.

% This program is written for offline simulation.
% file: adpcm.m
clear all; close all
load we.dat % Provided by the instructor

speech ¼ we;

desig speech;

lg ¼ length(desig);

¼

% Length of speech data

enc ¼ adpcmenc(desig); % ADPCM encoding

%ADPCM finished
dec ¼ adpcmdec(enc); % ADPCM decoding
snrvalue ¼ snr(desig,dec) % Calculate signal to noise ratio due to quantization
subplot(3,1,1);plot(desig);grid;
ylabel( ' Speech ' );axis([0 length(we) -8000 8000]);
subplot(3,1,2);plot(dec);grid;
ylabel( ' Quantized speech ' );axis([0 length(we) -8000 8000]);
subplot(3,1,3);plot(desig-dec);grid
ylabel( ' Quantized error ' );xlabel( ' Sample number ' );
axis([0 length(we) -1200 1200]);
Program 11.12. MATLAB function for ADPCM encoding.

function iiout ¼ adpcmenc(input)
% This function performs ADPCM encoding.
% function iiout ¼ adpcmenc(input)
% Usage:
% input ¼ input value
% iiout ¼ output index
%
% Quantization tables
fitable ¼ [000111137];
witable ¼ [-0.75 1.13 2.56 4.00 7.00 12.38 22.19 70.13 ];

qtable ¼ [ -0.98 0.62 1.38 1.91 2.34 2.72 3.12 ];

invqtable [0.031 1.05 1.66 2.13 2.52 2.91 3.32 ];

lgth ¼ length(input);
sr ¼ zeros(1,2); pk ¼ zeros(1,2);
a ¼ zeros(1,2); b ¼ zeros(1,6);
dq ¼ zeros(1,6); ii ¼ zeros(1,lgth);
y ¼ 0; ap ¼ 0; al ¼ 0; yu ¼ 0; yl ¼ 0; dms ¼ 0; dml ¼ 0; tr ¼ 0; td ¼ 0;
for k ¼ 1:lgth
sl ¼ input(k);

¼

%
% predict zeros