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    Here are the answers I received to my question about cross-correlation
    and cross-FFT software.

    ************************************************** ********
    From: Joergen Assentoft
    Subject: Re: cross-FFT or cross-correlation

    Try the company: MOMENTUM Data System, Phone 7145576884, FAX: 7145576969.
    The software can run on WINDOWS and SUN Sparc. You have also the
    possibility the make real-time A/D or D/A conversion and use a PC or SUN
    Sparc Board with a DSP-processor.

    ************************************************** ********
    From: (Mitchell Gil Maltenfort)
    Subject: Re: cross-FFT or cross-correlation

    Are you looking for packages or just useful bits of code? I have an FFT &
    cross-correlation routine I wrote that's fairly clear and reliable.

    Also, you might want to bear in mind that you can estimate the
    cross-correlations of velocity and/or acceleration from the
    cross-correlations of position. Since differentiation (and integration)
    are linear operators, you can play some interesting games. Check Bendat
    and Piersol's book "Random Data" and similar references.

    Personally, I don't trust coherence. It's basically the correlation
    coefficient of components at different frequencies, and assumes that X and
    Y are related by a linear system. Cross-correlation may give you a clearer
    result - besides the points I raised above.

    Mitchell Gil Maltenfort Northwestern University Chicago, Illinois

    ************************************************** ********
    From: richard@HMS01.HMS.UQ.OZ.AU
    Subject: Re: cross-FFT or cross-correlation

    With respect to the subject of your BIOMCH-L posting, I have previously used
    the statistical package BMDP to perform bivariate spectral analyses
    (cross-FFT). It wasn't something I pursued in great depth at the time,
    although it did seem to offer a lot of potential. I have thought of applying
    the technique to some of the data sets we are currently analysing.
    I have used both the Sun (SPARC) and PC versions of the software. I
    understand that academic prices are available. Simon Fraser University had a
    site licence for the Unix version of the program, which we able to install
    on our own machines in the lab. It is a very diverse set of routines, but
    they are generally quite straightforward to use. Although you could also
    achieve the same result with a package like MATLAB, this would involve a
    good deal more development. My impression is that BMDP would provide the
    information you require.
    Richard Carson.

    ************************************************** ********
    From: Graeme Wood
    Subject: Re: cross-FFT or cross-correlation

    I've used a commercially available package named TSA (Time Series Analysis)
    to perform cross-spectral analyses of EMG signals. Your application would be
    no different in principle. The package costs around AUD 600, and is
    available from Dr John Henstridge (the author) at Unit 8, 154 Hampden
    Road (P.O. Box 630), Nedlands, WA 6009, Australia. (Fax: +61-9-386 3202).

    Graeme A. Wood

    ************************************************** ********
    From: YUB@rcf
    Subject: RE: cross-FFT or cross-correlation

    Hi, Rosa,
    I think calculating the coefficient of multiple correlation between the right
    and left leg, and between your normal and abnormal subjects may be one of the
    techniques you can use. The details of the calculation of the coefficient of
    multiple correlation can be found in "Repeatability of kinematic, kinetic, and
    electromyographic data in normal adult gait" by Kadaba and et. al. in Journal
    of Orthopaedic Research, Vol 7, No. 6, 1989. The calculation of this
    CMC is very simiple. I believe you can write a program to do it without any
    difficulty, or you can use a statistic software package to do it.
    Good luck.

    Bing Yu, Ph.D.\

    ************************************************** ********
    From: Gary Kamen
    Subject: cross-correlation software

    If you stay in the time domain, you should be able to do cross-correlations
    with one of the statistical packages, like BMDP or SPSS. I have used
    a signal processing package called HYPERSIGNAL (Hyperception, Inc.,
    9550 Skillman LB125, Dallas, TX 75243, tel:214-343-8525) and this should
    also work, as well as handling the problem in the frequency domain.

    Gary Kamen
    Boston University

    ************************************************** ********
    From: Jill Whitall
    Subject: Re: cross-FFT or cross-correlation

    We (JoAnne Lazarus and I) have done cross-correlations using the
    Systat commercial package...very easy to use...let me know if you need
    more information..

    ************************************************** ********
    Thanks to all of you!
    Rosa M. Angulo-Kinzler