[sdiy] Fast envelope follower circuit needed..

Takuya Katayama pata at ieee.org
Fri Mar 29 07:35:53 CET 2013


Hi Brian and the Lists,

Oh, I see what you say and I understand problem in my argument.
Thank you.

Then, does a Sampling Amp fit to the requirement?
Sample at few kHz sampling clock, just like sampling clock is amplitude modulated by original signal's envelope.
Cut off freq. of LPF can be one-third of the sampling clock so "fast" enough to a few Hz or sub-Hz signal.

Taku

--- On Fri, 2013/3/29, rsdio at sounds.wa.com <rsdio at sounds.wa.com> wrote:

> 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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