Using a filter difference equation in a for loop to filter a .wav file within the loop

Based on the bandpass filter difference equation inside a for loop:

x = zeros (30,1);

y = zeros (30,1);

x(3,1) = 1;

for

y(n) = a1*x(n) + a2*x(n-1) + a3*x(n-2) - b1*y(n-1) - b2*y(n-2);

end

How can change a .wav file by running that difference equation through the audio?

Answer 1

[Mathieu NOE]

hello

see example below - notice b are usually coeffcient names for numerator so they are used for the x (input) , wheras a coefficients are for the denominator - output y (hence the transfer H = B(z^-1)/A(z^-1))

but you are free to use your own convention as soon as the coeffs have the good value !

enjoy

%% data
[x,Fs] = audioread('test_voice_mono.wav');

[samples,channels] = size(x);
dt = 1/Fs;
time = (0:samples-1)*dt;

%% IIR filter recursive equation 
c1 = 8;
c2 = 2;
c3 = 7;
b0 = 0.05 * c1;
b1 = 0.03 * c2;
b2 = 0.02 * c3;
a1 = 0.5;
a2 = 0.5;


% manual for loop coding IIR filter
y(1) = b0*x(1) + 0 + 0  + 0 + 0; % 1st iteration
y(2) = b0*x(2) + b1*x(1) + 0  + a1*y(1) + 0;  % 2nd iteration
for k = 3:samples % for iteration # 3 and after
    y(k) = b0*x(k) + b1*x(k-1) + b2*x(k-2)  + a1*y(k-1) + a2*y(k-2);
end


figure(1)
plot(time,x,time,y)

[Mathieu NOE]

hello

problem solved?