% M02-reverb.diary
% DT systems; Examples using convolution
% 2007-09-11

% 'Running a system' in matlab
% Because Matlab indices start at 1, we add 2 to allow us to reach back 
% to -1
n = -1:19;
% (i.e. n(2+ i) = i, mapping time to matlab)
x = zeros(1, 21);
y = zeros(1, 21);
% Set x[2] to a nonzero value
x(2+ 2) = 5;
% Run the system ("accumulator", from slide 6 of topic 2 slidepack)
for i = 0:19; y(2+ i) = x(2+ i) + y(2+ i-1); end
% Look at the results
subplot(211)
stem(n,x)
subplot(212)
stem(n,y)

% Simple convolution calculation
x=[0 3 1 2 -1];
h=[3 2 1];
subplot(321)
stem(x)
subplot(322)
stem(h)
% Convolve them
y = conv(x,h)
subplot(312)
stem(y)
% Same result if arguments in the other order
y = conv(h,x)

% Room reverb simulation
[h,sr] = wavread('hlwy16.wav');  % Recording of clap in hallway
soundsc(h,sr)
[d,sr] = wavread('mpgr1_sx419.wav'); % Speech example
soundsc(d,sr)
% Convolve them (SLOW because many thousands of points)
y=(conv(d,h));
% Listen to simulated reverberation
soundsc(y,sr)