Filtering EMG to make linear envelope - Butterworth filter or RMS

[Yusuke Okita]

Hi,

Yesterday, My colleague and I talked about how to make linear envelope from measured EMG during gait.
And we wondered why we generally choose Butterworth low-pass filter instead of Root Mean Square (RMS).
My opinion is that low-pass (zero-lag) filter is better because it might not change the time onset and offset compared with RMS.
I would be appreciative if you could some suggestions to us.

Best regards,
Yusuke Okita
Graduate student, Kyoto University

[Rodrigo Bini]

Re: Filtering EMG to make linear envelope - Butterworth filter or RMS

Hi,

Yesterday, My colleague and I talked about how to make linear envelope from measured EMG during gait.
And we wondered why we generally choose Butterworth low-pass filter instead of Root Mean Square (RMS).
My opinion is that low-pass (zero-lag) filter is better because it might not change the time onset and offset compared with RMS.
I would be appreciative if you could some suggestions to us.

Best regards,
Yusuke Okita
Graduate student, Kyoto University

Hi Okita,

in our lab, we found shifts in onset depending on the length of the time window for computing the moving averages.
I would go for the low pass filter.
Hope that helps.

Cheers,

[Yusuke Okita]

Re: Filtering EMG to make linear envelope - Butterworth filter or RMS

Hi Okita,

in our lab, we found shifts in onset depending on the length of the time window for computing the moving averages.
I would go for the low pass filter.
Hope that helps.

Cheers,

Dear Dr. Bini:

Thank you for your helpful information.
I agree with your idea on the length of the time window.

Best regards,
Yusuke