%part 4: Pick a telephone key of your choice.
%generate and plot a quarter second (.25sec) DTMF
%signal corosponding to that key. Use a sampling
%period T = 1/8000 sec. Use A1=A2=1
 
%5 key: 770 Hz and 1336 Hz
time2 = 0:1/8000:.25;
key5 = sin(2*pi*770*time2)+sin(2*pi*1336*time2);
%plot(time2,key5);
%title('part 4, 5 key');
%xlabel('time, seconds');
%ylabel('Amplitude');
 
%part 5: plot the magnitude spectrum of part 4 as
%learned in part 1
%omega2 = [-pi/(1/8000):(2*pi)/(length(time2)*(1/8000)):(-pi/(1/8000))+((length(time2)-1)*2*pi)/(length(time2)*(1/8000))];
Key5mag = abs(fftshift(fft(key5)));
plot([500:1500],Key5mag(500:1500));
title('Part 5');
xlabel('frequency Hz');
ylabel('Magnitude');
 
%Key5mag = psd(key5,'fs',8000);
%plot(Key5mag);
%sound(key5,8000);
 
%part 6: 
%3 key
tones1 = sin(2*pi*697*time2)+sin(2*pi*1477*time2);
%5 key
tones2 = sin(2*pi*770*time2)+sin(2*pi*1336*time2);
%7 key
tones3 = sin(2*pi*852*time2)+sin(2*pi*1209*time2);
%pause
pause = zeros(1,800);
tones = [tones1 pause tones2 pause tones3];
plot([0:1/8000:(length(tones)-1)/8000],tones);
title('Part 6, 3, 5, and 7 keys');
xlabel('time, seconds');
ylabel('Amplitude');

%part 7
sound(tones,8000);