hanning ,hamming window in matlab?

how do Hanning and Hamming window in matlab?

when must I do these window after DFT signal or before DFT signal?

Answer 1

[Wayne King]

Before you take the DFT

hamming() or hann()

t = 0:0.001:1-0.00;
 x = cos(2*pi*100*t)+randn(size(t));
 winvec = hamming(length(x)); % hann(length(x));
 xdft = fft(x'.*winvec);
 plot(abs(xdft))

[Mary Jon]

t = 0:0.001:1-0.00; no problem if length of my signal is 33?

[Mary Jon]

instead of x in your code, I will put my signal?is not it?

[Wayne King]

yes, I just did an example. Substitute your signal as desired.

[Mary Jon]

if I have 20 signals ,what I do , repeated this code 20 times

[Wayne King]

You can put them in a matrix and multiply them all at once.

X = randn(100,20);
 h = hamming(100);
 h = repmat(h,1,20);
 X = X.*h;

[Mary Jon]

How put 20 signals with length 33 in matrix? s1=first signal, s2=second signal,and so on and where is DFT in your code?

Answer 2

[Wayne King]

That depends on how they are in your workspace. If you have 20 separate vectors, then just do this.

I'll assume they are column vectors and I'll just create 3 signals here.

s1 = randn(33,1);
 s2 = randn(33,1);
 s3 = randn(33,1);
 Sig = [s1  s2 s3];

Now window them as before:

h = hamming(33);
 Sig = Sig.*repmat(h,1,3);

Now take the DFT

SigDFT = fft(Sig);

Obviously, you have to make adjustments for the 20 columns above:

repmat(h,1,20)

for example

[Mary Jon]

I have row vectors not column vectors, s1=[1 2 3 4] s2=[3 5 6 6] and so on

when applied yor code in to my signals I get this error

Error using ==> times Matrix dimensions must agree.

Answer 3

[Wayne King]

If you have row vectors you have to make the necessary adjustment. Just convert them to column vectors.

s1 = s1';

[Mary Jon]

if I want to plot each signal of SigDFT individually How do that? because of when I plot (SigDFT)signals, I get not clear plot or shape

[Wayne King]

You should plot abs()

 plot(abs(SigDFT))

[Mary Jon]

Thank you so much for every thing,Wayne