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help!! about the transfer function of filter.

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renwl

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I lookup the table of the chebyshev filter. The chebyshev filter I want to find is a third order filter with 0.5dB passband ripple. The polynomial I found is S^3+1.253*S^2+1.535*S+0.716.

What does the coefficient mean? It’s normalized to cutoff frequency, isn’t it? What’s the transfer function if the cutoff frequency is 4kHz and the gain is 0dB?

Thanks.
 

you can get the pole and zero of this function in matlab
 

If I find the pole and zero, is it normalized to cut-off frequency?
If it is , I can get the wanted pole and zero by multiplying the pole and zero by cut-off frequency, right?
 

correct.


renwl said:
If I find the pole and zero, is it normalized to cut-off frequency?
If it is , I can get the wanted pole and zero by multiplying the pole and zero by cut-off frequency, right?
Click to expand...
 

I dont think so.
for example,when the numerator is 1, the zero will be ∞.
all the poles are only determined by the denominator. so the poles are all multiplied by a number and zero is not.

how about the low frequency gain now? It will change,I think.
 

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