DTMF decode

[y fs] = wavread('random.wav');
plot(y);

tsamp = 0.01;
t = linspace(0,tsamp,tsamp*fs+1);
M = length(t);
N = floor(length(y)/M);
ys = reshape(y(1:(N*M)),M,N);

fL = [697 770 852 941];
fH = [1209 1336 1477 1633];
omega = 2*pi*fL';
w = exp(1j*omega*t);
yL = abs(w*ys)/M;
plot(yL');

omega = 2*pi*fH';
w = exp(1j*omega*t);
yH = abs(w*ys)/M;
plot(yH');

ndx = 1:4;
y1 = ndx*(yL>0.07);
subplot(2,1,1);
plot(y1);
ylabel('low freq index');
subplot(2,1,2);
y2 = ndx*(yH>0.07);
plot(y2);
ylabel('high freq index');

% look for zero to positive differences
% and then a few samples later
ndx = find(diff(y1)>0);
n1 = y1(ndx+2);
n2 = y2(ndx+2);
[n1' n2']

ans =

     2     3
     1     1
     2     1
     1     2
     1     3
     2     2
     3     2
     3     3
     3     1
     4     2

key = ['147*'; '2580'; '369#'; 'ABCD'];

for k=1:length(n1)
    pn(k) =key(n2(k),n1(k));
end
disp('phone number:');
disp(pn);

phone number:
6142358970

Published with MATLAB® 7.10