Determining median power frequency of an EMG signal

[BB24]

Hi,

I'm trying to calculate the median power frequency of a simple sEMG signal through a standard DAQ VI in LabVIEW without the use of the biomedical toolkit but I'm having trouble knowing where to start using a power spectrum. Any tips?

Thanks

[johnsold]

What is the exact mathematical definition of "median power frequency" as used in the EMG field?  Once you have that definition it is probably not too difficult to implemtn the algorithm in LV.  My experience with EMG has been that the field does many things empirically ("because it has always been done that way") so it is important to define the process first.

Lynn

[BB24]

I've seen it defined as the integral of the entire power spectrum and then the position of the halfway point of the curve is found. This then needs to correspond to the frequency responsible for it which is the median power frequency. I'm not too sure if that's right but that's what I understand about it so far. 

[Hatef.fouladi]

why you do not want use biomedical toolkit?
you can also change them for your system

[BB24]

I'm not really allowed to use the Biomedical toolkit for my project plus the computers that are available to me with the DAQ doesn't have it installed.

[Bob_Schor]

With that definition, you are "almost done".  What remains is defining your sample, and whether you are interested in time-varying changes, or merely "for this N-second sample of raw EMG, sampled at M Hz".  Once you have your sample defined, it should be easy to use the functions that come with LabVIEW to compute the Power Spectrum.  Once you have that, apply your definition of "Median Power Frequency".

Bob Schor

[BB24]

I'll assume I need to use the build waveform vi for a real time signal to define the sampling rate. I've already computed the power spectrum but applying my definition of mdf is where I'm still unsure of as there are various integral VIs to use.

[Bob_Schor]

You can "integrate" the old-fashioned way.  If you have the Power Spectrum as an array, say Power(i), i = 0..511, then replace Power(i) by sum(Power(k), k = 0 .. i) and you'll have Integral(Power).  Now find for what value of i IntegralPower(i) = 0.5*IntegralPower(511).  Note IntegralPower(511) = sum(Power(i), i=0..511).

Bob Schor

[BB24]

Ok I have the integral and halved value of that done. I'm now trying to use a while loop to find the frequency corresponding to the half of the power but I'm getting errors. Any last tips? 

[Bob_Schor]

Yes -- post your code so we can see where your conceptual mistake is located.

Bob Schor