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

%first tone
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

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

%second tone
F0a=8000; %frequency of source
F1a=F0a*c./(c+v_o); %observed frequency as source gets closer
F2a=F0a*c./(c-v_o); %observed frequency as source gets further
F3a=fliplr(F2a);
F4a=[F3a F1a]; %frequency matrix

y=sin(2*pi.*F4a.*t); % signal equation

%fthird tone
F0b=5746; %frequency of source
F1b=F0b*c./(c+v_o); %observed frequency as source gets closer
F2b=F0b*c./(c-v_o); %observed frequency as source gets further
F3b=fliplr(F2b);
F4b=[F3b F1b]; %frequency matrix

z=sin(2*pi.*F4b.*t); % signal equation

three_tone=b3.*(x+y+z);

% plot frequency, amplitude, & velocity

figure(1)
plot(t,three_tone);
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)
subplot(3,1,1)
plot(t,F4);
xlabel('Time (s)'); ylabel('Frequency (Hz)'); Title('Dopper Effect: The apparent frequency of the source, F0=440Hz');
subplot(3,1,2)
plot(t,F4a);
xlabel('Time (s)'); ylabel('Frequency (Hz)'); Title('Dopper Effect: The apparent frequency of the source, F0a=8000Hz');
subplot(3,1,3)
plot(t,F4b);
xlabel('Time (s)'); ylabel('Frequency (Hz)'); Title('Dopper Effect: The apparent frequency of the source, F0b=5746Hz');

wavwrite(three_tone,Fs,'doppler3'); %save the sound