Envelope calculation using Matlab...

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S Dodd
S Dodd 2012-9-29
If I have a digital sampled waveform (for example sampled at 10kHz) and a set of uneven envelope points (say 4 or 5) - how can I use Matlab to work out the following:
Assume the sampled waveform dips into the envelope on several occasions but the majority of the time it should be completely outside of the envelope. I want to calculate what percentage of the overall area of the defined envelope was covered by entries of the sampled waveform into it.
I'm a Matlab beginner so any sample code would be greatly appreciated.
Here is a link to a sketch of a typical waveform: https://picasaweb.google.com/116715492473256943579/Matlab?authuser=0&authkey=Gv1sRgCKqT7Z2PndbYvAE&feat=directlink

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回答（1 个）

Image Analyst
Image Analyst 2012-9-29
Not sure what this means. Do you have a diagram to illustrate what "encroaching" means to you? Do you mean something like
aboveUpperEnvelope = signal > upperEnvelope;
belowLowerEnvelope = signal < lowerEnvelope;
And then just say it's 100% if the signal is within the envelope and it's some fraction if the envelope is within the signal? And the percentage depends on where the zero line is. Is your upper envelope just the negative of your lower envelope, or are they both offset and raised above the x axis?
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S Dodd
S Dodd 2012-9-30
The envelope points would be made up of a set of x-axis time points with corresponding y-axis power points.
S Dodd
S Dodd 2012-10-11
The envelope is made up of a series of straight lines whereas the actual waveform is a much higher resolution set of data points that is smoothed.

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