Re: Butterworth Filter

Mac wrote:
> On Wed, 22 Jun 2005 15:20:18 -0700, dhruveenews@xxxxxxxxx wrote:
>
>> Hello,
>> I am working on data acquisition. I have collected some EMG data
>> and now according to the research papers, the EMG data has to be
>> filtered using 2nd order dual pass butterworth filter with the
>> cut-off frequency of 40 Hz. What is 'dual pass'? Can anyone
>> elaborate on it.
>>
>> thank you
>
> Maybe dual pass means you have to put the data through the filter
> twice, once forwards, and once backwards.
>
> --Mac

Yeah, this would indicate a digital filter.
But when an analog filter is meant, maybe it is a cascaded Butterworth,
which forms a Linkwitz-Riley filter of 4th order. The word "dual pass" is
meaningful only inthe digital domain.
--
ciao Ban
Bordighera, Italy


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