No announcement yet.


This topic is closed.
  • Filter
  • Time
  • Show
Clear All
new posts

  • filtering

    Here we go again with the filtering issue.

    In the process of analyzing some wrist kinematic data that we collected
    with the use of electrogoniometers, an interesting question was raised
    by one of our graduate students.

    Background: Our interest is to look at position, velocity and acceleration
    of the wrist during various tasks. Since the electrogoniometers provide
    position data, we differentiate the signal once for the velocity
    and twice for the acceleration data. In order to eliminate noise
    in the signal we use a fourth order, zero phase shift, Butterworth filter
    with a cut-off frequency of 6 Hz. This filter is applied to the raw position

    His question was: should we apply the filter to the data again after each step
    where the signal has been differentiated. His logic was that the process
    of differentiating the signal would create a higher frequency component
    in the signal. So, in essence we would filter the raw position data,
    differentiate the signal to get velocity, filter the velocity data, then
    differentiate the signal to get acceleration.

    After looking through several reference books, notes, literature, etc.
    I could not find anywhere that anyone does that. I also could not find
    arguments either supporting or refuting this idea.

    I would appreciate any comments either rejecting or supporting
    the use of filtering the velocity data before calculating the acceleration.

    What would be the net effect of filtering a second time?

    Thank you in advance.

    I will be glad to post the comments.


    ************************************************** ******************
    Guy G. Simoneau, Ph.D., P.T., A.T.C.
    Assistant Professor, Physical Therapy Department
    Marquette University
    Walter Schroeder Complex, Room 346
    P.O. Box 1881
    Milwaukee, WI 53201-1881

    Phone: 414-288-3380
    Fax: 414-288-5987
    ************************************************** ******************

    To unsubscribe send UNSUBSCRIBE BIOMCH-L to
    For more information: