Fs=8000;
Ts=1/Fs;
c=345;
L=input('What is the distance from the source to the observer? ');
d=input('What is the distance of the observer offset from the source path? ');
v=input('What is the velocity of the source? ');
T=L/v; % time it takes for source to move to the midway point is distance/velocity
ti=0:Ts:T; % time from the beginning to the midpoint
tf=T:Ts:(2*T); % time from the midpoint to the end
t=[ti tf]; %matrix for times
L1=v*ti; %distance traveled after ti
v_o=v.*cos(atan(d./L1)); %observed velocity
H=sqrt((L1.^2)+(d^2)); %hypotenuse, distance between observer and source at time 0

b=.8;       %amplitude
b1=b./(H+1);
b2=fliplr(b1);
b3=[b2 b1]; %amplitude matrix

F0=440; %frequency of source
F1=F0*c./(c+v_o); %observed frequency as source gets closer
F2=F0*c./(c-v_o); %observed frequency as source gets further
F3=fliplr(F2);
F4=[F3 F1]; %frequency matrix

y=b3.*sin(2*pi.*F4.*t); % signal equation

% plot frequency, amplitude, & velocity

figure(1)
plot(t,y);
xlabel('Time (s)'); ylabel('Velocity (m/s)'); Title('Dopper Effect: Velocity of source relative to observer');

figure(2)
plot(t,b3);
xlabel('Time (s)'); ylabel('Amplitude'); Title('Dopper Effect: The signal envelope');

figure(3)
plot(t,F4);
xlabel('Time (s)'); ylabel('Frequency (Hz)'); Title('Dopper Effect: The apparent frequency of the source');

wavwrite(y,Fs,'doppler2'); %save the sound