butterworth filter

Hello I am an engineering student, relatively new with filters and matlab,
I need to design a bandpass butterwoth filter with 2 bands in matlab using
the buttord function. I know how to do it for just one band and iwas trying
to apply the same approach using 2 bands but i did not work. My questions
are: Do i have to design 2 separated bandpass filters and combine them or
is there a way do it together using the buttord function using the 4 pass
band edge frequencies

Thanks

On Mar 28, 12:44 am, "madrid" <len...@starmedia.com> wrote:
> Hello I am an engineering student, relatively new with filters and matlab,
> I need to design a bandpass butterwoth filter with 2 bands in matlab using
> the buttord function. I know how to do it for just one band and iwas trying
> to apply the same approach using 2 bands but i did not work. My questions
> are: Do i have to design 2 separated bandpass filters and combine them or
> is there a way do it together using the buttord function using the 4 pass
> band edge frequencies
>
> Thanks

Best to design them separately then cascade.

H.S

Hardy.Spicer@yahoo.co.uk wrote:
> On Mar 28, 12:44 am, "madrid" <len...@starmedia.com> wrote:
>> Hello I am an engineering student, relatively new with filters and matlab,
>> I need to design a bandpass butterwoth filter with 2 bands in matlab using
>> the buttord function. I know how to do it for just one band and iwas trying
>> to apply the same approach using 2 bands but i did not work. My questions
>> are: Do i have to design 2 separated bandpass filters and combine them or
>> is there a way do it together using the buttord function using the 4 pass
>> band edge frequencies
>>
>> Thanks
> 
> Best to design them separately then cascade.

Think again. That way you will only get that band which id part of the 
passband of both. If those don't overlap, you get nothing.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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