Greetings Freaks -
I don't have an instantaneous application for this, so it is more "academic" than practical. But, I CAN see a potential application in my accelerometers, so there is some real-world, here. Thus, it is NOT a troll, but a sincere question.
Suppose that you have a "signal" which consists of a high frequency component, a low frequency amplitude modulation of the high frequency component, and maybe quite a bit of noise. For data reduction, and because it is what the situation calls for, I want to store the "envelope" rather than the point-by-point digitization of the combined signal in real time.
The question is: How to do this with the limited power of a non-DSP micro (assuming that all of the sample rates, etc, are within the capability of what-ever chip is chosen)?
For example, suppose that I have sequential samples Xm and Xn. Lets further suppose that the values of X have been increasing for several samples, up to Xm. Now, Xn is less than Xm. Is Xm a peak that represents a point on the envelope? Or, is Xn just a momentary noisy deviation, only to be followed by a sample that is larger than Xm? You can't know at sample n because you cannot "see" the future.
So, it would seem like you have to evaluate over some extended interval. Maybe you evaluate over a an interval that is a bit longer than the expected period of the high frequency component and look for the maximum and minimum within that interval? Or, maybe that is not such a good test and maybe there is something better? Or., maybe its not such a good test, but it is as good as it gets? If that is an appropriate test, should the interval be a running interval or should it be in sequential blocks?
At this point, I am wondering if anyone, here, has tried to implement something like this? Or, has anyone tried some other method? If so, what were your experiences?