How to check a filter

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Daniel
Daniel 2016-5-26
评论： Star Strider 2016-5-26
i created a filter using FDATOOL. now i want to check it. i did : generate matlab code. got a mutlab function with the filter specification. ran the function and got a matlab object Hd. this is ment to be a HPF: samling at 20MHz Fstop 10KhZ Fpass 500KHz
i want to run this filter with a signal and see resault. thought about entering a sine function: not sure that its the right way, i coded:
Fs=20e6;
dt=1/Fs;
stopt=0.25;
t=(0:dt:stopt-dt)';
Fc=10e3;
x=sine(2*pi*Fc*t);
y=filter(Hd,x);
i expect not to see anything when setting the sine Fc below 10Khz but thats not the case now i am not sure i am doing things correct. would like to get some help

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回答（1 个）

Star Strider
Star Strider 2016-5-26
If you want to view the transfer function, use the freqz function.
See the documentation on it for all the options it provides.
  2 个评论
Daniel
Daniel 2016-5-26
i get the same plot i got from the fdatool. i want to test it. i want to pass a sine function through my filter and see what happens. cant seem to do that. i dont get a 1:1 on the pass band. and see a distorted signal. did i ran the filter correctly?
Star Strider
Star Strider 2016-5-26
Use the filtfilt function, not filter. The first creates a phase-neutral (maximally flat phase response), and the other introduces phase distortion.
If your sin signal is near the filter cutoff frequency or in the transition region, it could be distorted even if you use filtfilt. That is likely since your filter has a very large transition region, going from 10 kHz to 500 kHz.

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