Calculate envelope curve x spacing

Hi,
I have a sinusoidal voltage signal where the amplitude changes with time.  I want to determine the amplitude's dependence on another variable, so I need to separate out the oscillatory information.  I tried using the calculate envelope curve function, but the x channel spacing is not equidistant - you can't combine the x and y channels to make a waveform channel - so I don't know how to compare these channels with my other data (i.e. using regression). 
It seems that the envelope function goes through the data set and selects out all of the extreme points, divides these between upper and lower bounds, and puts these data points in the new channels.  Is there some function that would allow me to set up an x channel with equally spaced points, and interpolate the corresponding values for the envelope?
I tried using a curve fit to approximate the amplitude data, but it doesn't retain enough of the features.
Thanks, Myra
Solved!
Go to Solution.

Hi Myra,
It sounds like the key issue you're facing is that you have one curve with non-equadistant X values and a second curve with equadistant values, and you want to compare the Y values of those 2 curves at exactly the same X values.  This is what the "Linear Mapping" function in the ANALYSIS Curve Fitting palette does.  Just provide the X and Y channels of the non-equadistant curve in the first two dialog fields and the X channel of the equadistant curve in the third field.  This will create a linearly interpolated version of your non-equadistant curve that has exactly the (equadistant) X values as your other curve.
If your equadistant X value curve is a waveform, then you'll need to first use the "Numeric Channels <=> Waveform Channels" function from the ANALYSIS Channel Functions palette, in oder to create that X channel you'll need in the third dialog field as described above.
Ask if you have further questions,
Brad Turpin
DIAdem Product Support Engineer
National Instruments

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