dtmf_gen.m

用dsp解压mp3程序的算法

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% dtmf_gen.m - This program generates all the coefficients of IIR
%              for DTMF tone generator
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

clear all; close all

% low freq group: fL = 697, 770, 852, 941 Hz

fL = [697 770 852 941];

% High freq group: fH = 1209, 1336, 1477, 1633 Hz

fH = [1209 1336 1477 1633];

% Coefficients for numerator

b0 = 0;
b1_fl = sin(2*pi*fL(1:4)/8000);
b1_fh = sin(2*pi*fH(1:4)/8000);
b2= 0;

b0_v = zeros(1,8);
b1_v = [b1_fl b1_fh];
b2_v = zeros(1,8);
b_v = [b0_v; b1_v; b2_v];


% Coefficients for denomerator

a0 = 1;
a1_fl = -2.*cos(2*pi*fL(1:4)/8000);
a1_fh = -2.*cos(2*pi*fH(1:4)/8000);
a2 = 1;

a0_v = ones(1,8);
a1_v = [a1_fl a1_fh];
a2_v = 1.*ones(1,8);
a_v = [a0_v; a1_v; a2_v];


% Select the keypad

key = [ '1' '2' '3' 'A'; '4' '5' '6' 'B'; '7' '8' '9' 'C'; '*' '0' '#' 'D'];

% User input a key

R = input('Key in the touch pad: ','s');
[i,j]= find(R == key);
while i == [ ];
    disp('Wrong Key!!');
    R = input('Key in the touch pad: ','s');
    [i,j]= find(R == key);
end    

% Display the key pressed

b1_first = b1_fl(i); a1_first = a1_fl(i);
b1_second = b1_fh(j); a1_second = a1_fh(j);
figure;
freqz([b0 b1_first b2], [a0 a1_first a2]); hold on;
freqz([b0 b1_second b2], [a0 a1_second a2]); 
title('Frequency response of tone');

% Sound output (50 msec tone)

[H1,T] = impz([b0 b1_first b2], [a0 a1_first a2],400,8000);
[H2,T] = impz([b0 b1_second b2], [a0 a1_second a2],400,8000);
HT = H1+H2;
soundsc(HT);
figure; plot(T,HT); title('Impulse response of 50 msec tone');
figure; psd(HT); title('Power spectrum density of tone');

save tx_data_5 HT;