stupid envelope follower idea

[Ian Fritz]

Hi Terry --

> RMS detection is a means of calculating the "area under the curve" of the
> waveform.

Huh?  :-)

The area under the curve of a waveform is zero. (Assuming ac coupling, or,
equivalently, ignoring the zero frequency Fourier component.)

> It is commonly done by squaring the instantaneous points of the
> waveform with an analog multiplier.  The peak voltage squared yields the
> RMS power.

Well -- it's (1) square the voltage, (2) average over a cycle, then (3) take
the square root.

But since the instantaneous power is independent of the phases of the
various Fourier components, the phase shifts you are concerned about don't
matter. They change the instantaneous waveform amplitude, but not the RMS
value.

> I hope that's right, I'm going by memory here.   The problem
> with that approach might be the time altered waveform might not have the
> same "area under the curve" as the original waveform.  It should be
> possible to do a mathmatical analysis or simulation to answer your
> question, maybe someone on the list has the means to do so, unfortunately
I
> don't.

I think the math is simple. The RMS voltage is the square root of the sum of
the squares of the Fourier amplitudes. Phases don't matter.

  Ian