% Program 11_1
% Dual-Tone Multifrequency Tone Detection
% Using the DFT
%
clf;
colordef black;
d = input('Type in the telephone digit = ', 's');
symbol = abs(d);
tm = [49 50 51 65;52 53 54 66;55 56 57 67;42 48 35 68];
for p = 1:4;
   for q = 1:4;
      if tm(p,q) == abs(d);break,end
   end
   if tm(p,q) == abs(d);break,end
end
f1 = [697 770 852 941];
f2 = [1209 1336 1477 1633];
n = 0:204;
x = sin(2*pi*n*f1(p)/8000) + sin(2*pi*n*f2(q)/8000);
k = [18 20 22 24 31 34 38 42];
val = zeros(1,8);
for m = 1:8;
   Fx(m) = gfft(x,205,k(m));
end
val = abs(Fx);
stem(k,val,'g'); xlabel('k');ylabel('|X[k]|');
grid on
limit = 80;
for s = 5:8;
   if val(s) > limit,break,end
end
for r = 1:4;
   if val(r) > limit,break,end
end
disp(['Touch-Tone Symbol = ',setstr(tm(r,s-4))])