Apply FIR and IIR filter to a audio file

FIR transfer function:

[x,fs] = wavread('sound.wav');
r = round(fs*0.3); % 0.3 second delay
b = zeros(1,r+1);
b(1) = 1;
alpha = 0.5;
b(r+1) = alpha;
y = filter(b,1,x);
wavplay(y,fs);

IIR transfer function:

[x,fs] = wavread('sound.wav');
r = round(fs*0.3); % 0.3 second delay
b = zeros(1,r+1);
b(1) = 1;
alpha = 0.5;
b(r+1) = alpha;
y = filter(1,b,x); % echo
wavplay(y,fs);