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28th January 2009, 02:47 #1
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convolution in matlab without using conv
hi!
i am suppose to design a low pass filter(lpf) using any window methods without uisng builtin functions in matlab. and the output should be a frequency response of the filter.
i could find coefficients of window(simply by substituting the formula for one of the windows) but designing the lpf without using the builtin functions has been very irritating !!
if anyone could help me concerned with this i will be very thankful!!!
thank you!

28th January 2009, 02:47

28th January 2009, 17:49 #2
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fir filter without matlab function
baladrg1987,
Any good book on digital signal processing or digital filters will show the technique. Also, see:
.
http://ocw.mit.edu/NR/rdonlyres/070A...4D/0/lec09.pdf
Regards,
Kral
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28th January 2009, 21:12 #3
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matlab built filter from coeff
This is a typical project to give you some handson experience with digital FIR filters. If you have some feeling with the theory, you should be able to do this :
 Rectangular frequence response (store in an vector)
 inverse dft on it
 apply window
there the filter is.
The frequency response is the opposte :
 take the filter coeficients
 apply dft

29th January 2009, 02:43 #4
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how to apply a filter in matlab
thank you mr.kral and svhb!

29th January 2009, 13:07 #5
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matlab filter function
Originally Posted by svhb
Please i want some help in using fdatool in matlab. I designed my filter but don't know how to apply it to my signal.
I do export the filter as an object or to workspace or as an SOS matrix, or even as an mfile. But i can't apply this filter to my original signal.
How can i get that.
Or if u suggest any other method for me to design a BPF and apply it to my signal.
I've really got confused.
Thanks in advance.

29th January 2009, 13:07

30th January 2009, 21:14 #6
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dft filter in matlab
For a FIRfilter : if you have your filter coeficients, you use concolution to apply it to your signal. (this is basically how the filter works).
Code:w = conv(u,v) convolves vectors u and v. Algebraically, convolution is the same operation as multiplying the polynomials whose coefficients are the elements of u and v.

30th January 2009, 21:14

16th February 2009, 11:27 #7
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matlab programs of dft without builtin function
Originally Posted by svhb
so, which function should i use to apply the filter to my signal.
I've used the function
filter(num,den,x) %%% where x=my data signal
but i have no result.
The code that u've written of using conv(u,v)
I think it can't work coz my coefficients r 2 vectors, num & den
and i want to apply it on my signal x
but, the conv function have just 2 arguments.
Is there any other function that works for my num & den coefficients.
Please... help
And, sorry for interruption.

16th February 2009, 20:50 #8
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matlab built in functions code
Num and den are the coeficients for the polynomials defining A and B in
H(Z) = B(Z)/A(Z)
When the coeficients of A are zero, except the first one, you made a FIR filter, and just divide all coeficient from B with a0. This is the impulse respone of the filter, and is finite (Finite Impluse Response filter). You can use these coeficients to do a convolution with your input signal.
When there are other coeficients than the first one of A are nonzero, you made an IIR filter (Infinite Impulse response filter). You can find the impulse respone by dividing the polynomials A and B, and you will see it never ends (but the results become smalleer and smaller, I hope). Because the impulse response never ends, it's inpractical to do with convolution.
If you look at how a digital filter works, it will be not to difficult to apply the filter to any input signal.

17th February 2009, 02:56 #9
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calculate the inverse of a fir filter in matlab
Originally Posted by svhb

17th February 2009, 19:33 #10
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matlab code without inbuilt functions
indeed it needs to be the discrete version of the transform, with DFT, I mean Discrete Fourrier Transform.

25th February 2009, 23:46 #11
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using a filter as window matlab
thanks to svhb

25th February 2009, 23:46

27th February 2009, 04:36 #12
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convolution matlab without using conv
get ur transfer function from coefficent of filters by using tf(z,p) then multiply it wuth ur input

10th March 2009, 22:04 #13
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filters without using matlab function
see this file will help you too much
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