% Pat O'Keefe
% Project 1
% Part 1

close all;
clear all;

% define sampling rate and set up a time vector
Fs = 8000;
TotalTime = 4;
t = -TotalTime/2+1/Fs:1/Fs:TotalTime/2;

c = 345; %speed of sound

freq = 350; % frequency of the source

vSource = 15; % velocity of the source

distance = vSource*t; % horizontal position of source w.r.t. observer

envelope = 1.0./distance; % envelope of the sound

% initialize vector
f = zeros(1,length(t));

% apply doppler effect and limit envelope
for i = 1:length(t)
    if t(i)<=0
        f(i) = freq*c/(c-vSource);
    else
        f(i) = freq*c/(c+vSource);
    end

    if abs(envelope(i)) > 0.5
        if( sign(envelope(i)) ~= 0)
            envelope(i) = 0.5*sign(envelope(i));
        else
            envelope(i) = 0.5;
        end
    end

end

% turn into final sound and normalize
x = envelope.*cos(2*pi*f.*t);
x = x/max(abs(x));


figure(1)
plot(t,vSource*ones(1,length(t))); grid on;
title('Velocity of Source Relative to Observer - Part 1');xlabel('Time (sec)');ylabel('Velocity');

figure(2)
plot(t,envelope);grid on;
title('Signal Envelope - Part 1');xlabel('Time (sec)');ylabel('Amplitude');

figure(3)
plot(t,f);grid on;
title('Apparent Frequency of Source - Part 1');xlabel('Time (sec)');ylabel('Frequency (Hz)');

sound(x,Fs);

Published with MATLAB® 7.7