[sdiy] Fast envelope follower circuit needed..

rsdio at sounds.wa.com rsdio at sounds.wa.com
Fri Mar 29 07:17:00 CET 2013

I disagree.

RMS and True RMS are decidedly not going to give you the envelope of  
the signal. By definition, not even true RMS will give you the peaks  
of the signal.

When designing a power supply, or measuring the power delivered by,  
e.g., 60 Hz 120 VAC, true RMS is a laudable goal. But the assumptions  
there are that all you care about is the power delivered, and not the  
peaks or the envelope of the signal. One assumes that AC power does  
not have a changing envelope.

As D. cheater pointed out, what really matters is the definition of  
"fast" and the definition of "envelope" that Jean-Pierre is looking  
for. Unless true RMS is part of his goal, then a true RMS circuit is  
vastly incorrect. For one thing, true RMS will certainly not deliver  
a rectified 0-5 V wave from a +/-2.5 VAC waveform.

Brian Willoughby
Sound Consulting

p.s. that tutorial sure is informative, though!

On Mar 28, 2013, at 20:11, Takuya Katayama wrote:
> I think true-RMS circuit is better.
> See ADI's tutorial
> http://www.analog.com/static/imported-files/tutorials/MT-081.pdf
> ICs are little expensive, so yu can use Ring Modulator and LPF.
> Taku

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