Question

Matlab filter responce and magnitude of filter question.

I have been working on this HW and I am not sure if I did something wrong. Here is my code.

%y[n]=x[n]+x[n-1]-x[n-4]-x[n-5];

%y[n]=y[n-1]-.9*y[n-2]+x[n]+x[n-1]

clear

clc

[x,fs] = audioread('toto.wav');

x = x(:,1);

dt = 1/fs;

t = 0:dt:(length(x)*dt)-dt;

plot(t,x); xlabel('Seconds'); ylabel('Amplitude');

num=[1 1 -.9];

den=[1 1 0 0 -1 -1];

sys=tf(num,den);

k=filter(num,den,x);

subplot(3,1,1);

plot(t,k);

title('filter response');

w=0:0.001:pi;

[h,om]=freqz(num,den,w)

m=20*log10 (abs(h))

an=angle(h)

subplot(3,1,2)

plot(om/pi,m)

title('mag spectrum of filter')

xlabel('freq')

ylabel('mag in db')

subplot(3,1,3)

plot(om/pi,an)

title('phase spectrum of filter')

xlabel('freq')

So I was playing around and when I use the 2nd equation at the top like in this code my filter response or the magnitude don't change. Why is that? Did I do something wrong? It doesn't even change if I change the values of the den either.

Answer 1

Dear user,

I think you are doing mistake in num ,den remaining code seems to be good

For this equation y[n]=x[n]+x[n-1]-x[n-4]-x[n-5];

use num=[1 1 0 0 0 -1 -1];den=[1];

For other equation

use

num=[1 1]; den=[1 -1 0.9];

%%

When these two edits are made code is working fine

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%y[n]=x[n]+x[n-1]-x[n-4]-x[n-5];

%y[n]=y[n-1]-.9*y[n-2]+x[n]+x[n-1]

clear

clc

t=0:1/44100:2;
fs=44100;
%x=cos(2*pi*5*t)+cos(2*pi*4*t)+cos(2*pi*15*t)+cos(2*pi*20*t);
%x=x';
x = x(:,1);

dt = 1/fs;

t = 0:dt:(length(x)*dt)-dt;

plot(t,x); xlabel('Seconds'); ylabel('Amplitude');

num=[1 1 0 0 0 -1 -1];

den=[1 ];

sys=tf(num,den);

k=filter(num,den,x);

subplot(3,1,1);

plot(t,k);

title('filter response');

w=0:0.001:pi;

[h,om]=freqz(num,den,w)

m=20*log10 (abs(h))

an=angle(h)

subplot(3,1,2)

plot(om/pi,m)

title('mag spectrum of filter')

xlabel('freq')

ylabel('mag in db')

subplot(3,1,3)

plot(om/pi,an)

title('phase spectrum of filter')

xlabel('freq')

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Outputs:

for

y[n]=y[n-1]-.9*y[n-2]+x[n]+x[n-1]

and

for y[n]=x[n]+x[n-1]-x[n-4]-x[n-5];

note: I have used sinusoidal signals sampled at 44.1kHz to simulate above .I have commented them just use my code and pass your signal.

So i think mistake is in num ,den

Please let me know if you have any doubts

Thank You.