In MATLAB:

The DTMF (Dual Tone Multiple Frequencies) tones are used in signaling over telephone lines. Use the script dtmfDemoTemplate.m:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % Ask user to press a key, then play the sum of DTMF tones % corresponding to that key. Also plots the resulting signal. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Fs = 8192; % sampling frequency (Hz) tVec = 0:1/ Fs :1/2; % sample times , from 0 to 0.5 seconds

while 1 keypressed = input('press any digit or * or #: ' ,'s'); % Set the two frequencies (in Hz) if keypressed == '1'

F1 = 697; F2 = 1209; elseif keypressed == '2' F1 = 697; F2 = 1336;

%%% INSERT YOUR CODE HERE. DON"T FORGET '*' and '#' else

fprintf(' Key not recognized; quitting. ');

break; end

% Construct signal as sum of two cosines, one with % frequency F1, and one with frequency F2. Each should % be sampled at times in tVec. Hint: for example, a % "middle A" pure tone would be cos(2*pi*440*tVec).

signal = %%% INSERT YOUR CODE HERE

% Play the sound

sound(signal ,Fs);

% Plot the signal

fprintf([' F1 = ' num2str(F1) 'Hz, F2 = ' ... num2str(F2) 'Hz ']);

figure(1);clf; plot(tVec,signal); xlabel('time (seconds)'); title(['Pressed ' keypressed ': F1 = ' ...

num2str(F1) 'Hz, F2 = ' num2str(F2) 'Hz']);

Insert code in the locations marked "INSERT YOUR CODE HERE". The script should ask user to press a key, then play the correct sum of DTMF tones corresponding to the key pressed, and also produce a plot of the signal.