Dear Miss Jain,
The dwt-command performs a single-level one-dimensional wavelet decomposition with respect to either a particular wavelet ('wname', see wfilters for more information) or particular wavelet decomposition filters (Lo_D and Hi_D) that you specify. This means that a filter is used to include certain frequencies in your wavelet data. For more information you can look at dwt example how to implement this in your code.
A second method would be to use a low or high pass filter with the filter-command:
clc;clear all;close all;
load noisdopp;
s = noisdopp;
subplot(3,1,1)
plot(s);grid on; title('original signal')
subplot(3,1,2)
b = [1 -1];
a = [1 -0.9];
c = filter(b,a,s);
plot(c);grid on; title('high pass filter')
subplot(3,1,3)
b = 1;
a = [0.5 -0.5];
c = filter(b,a,s)
plot(c);grid on;title('low pass filter')
Good Luck! Christiaan
