Talk:Envelope detector

message: It would be helpful if someone could explain why these things work the way they do. Mathematically it is clear, but what makes the diode do the right thing? - 72.58.19.66 08:09, 7 May 2006 (UTC)
replies: text: For the benefit of others: LC circuit seems to answer my question. - 72.58.19.66 08:12, 7 May 2006 (UTC)
thread_title: Why do these things work?

message: The article was rated as start-Class because it has several useful sections and a good image, but lacks content in those sections. Steven Hepting 07:26, 12 April 2007 (UTC)
thread_title: Article Rating

message: Dick Lyon removed from this article this material with the one-line explanation:
::"the definition of envelope in this example is not compatible with the definition that is the subject of this article." 
===Reverted example===	
A commonly used example in both space x and time t is that of the superposition of two waves of almost the same wavelength and frequency:
	
 	
 	
:f(x, \ t) = \sin \left[ 2 \pi \left( \frac {x}{\lambda - \Delta \lambda } - ( \omega + \Delta \omega )t \right) \right] + \sin \left[ 2 \pi \left( \frac {x}{\lambda + \Delta \lambda } - ( \omega - \Delta \omega )t \right) \right] 
 	
:::\approx 2\cos \left[ 2 \pi \left( \frac {x} {\lambda_{mod}} - \Delta \omega \ t \right) \right] \ \sin \left[ 2 \pi \left( \frac {x}{\lambda} - \omega \ t \right) \right] \ , 
which uses the trigonometric formula for the addition of two sine waves, and the approximation Δλ<<λ:
 	
:\frac{1}{\lambda \pm \Delta \lambda}=\frac {1}{\lambda}\ \frac{1}{1\pm\Delta \lambda / \lambda }\approx \frac{1}{\lambda}\mp \frac {\Delta \lambda}{\lambda^2} .
 	
Here the modulation wavelength λmod is given by:
	
	
 	
: \lambda_{mod} = \frac {\lambda^2}{\Delta \lambda}\ . 
	
The modulation wavelength is double that of the envelope itself because each half-wavelength of the modulating cosine wave governs both positive and negative values of the modulated sine wave.
	
Comparison with the earlier formula for a modulated wave shows that in this case the modulating envelope function R(t) is:
 	
:R(t) = 2\cos \left[ 2 \pi \left( \frac {x} {\lambda_{mod}} - \Delta \omega \ t \right) \right] \ . 
===References===
	 
 
As pointed out in this text, this example is a generalization from a a presentation based upon time alone to the case of an analog modulated wave propagating in space as well as varying in time. Personally I see nothing incompatible in this example: it is simply a minor generalization to consider propagation as well a time variation. 
Besides its interest as an academic generalization, this example also is an introduction to similar cases used in phenomena ranging from radar and GPS signals to electronic distance measurement. Brews ohare (talk) 01:44, 7 April 2012 (UTC)
replies: text: Brews, it is perhaps trivial to you that this sort of signed envelope is not at all what an envelope detector detects, nor is it like an analytic envelope, which is a fair description of what an envelope detector attempts to estimate.  Personally, I don't see how this adds to the article, but I'll listen to other opinions.  Dicklyon (talk) 04:39, 7 April 2012 (UTC)
replies: text: Dick: I take your point. Although the subsection Definition of the envelope appears to intend a general discussion of envelopes in AM modulation, in fact it doesn't do this, and in fact, a general definition is not needed for the topic of detection. The article Envelope (waves) should be written instead of redirecting here. Maybe this material would be appropriate there? Brews ohare (talk) 11:56, 7 April 2012 (UTC)
replies: text:  I would suggest Beat (acoustics) as a fitting place for this stuff. Olli Niemitalo (talk) 17:57, 8 April 2012 (UTC)
replies: text: I have placed this material in the new article I've written called Envelope (waves). Brews ohare (talk) 17:01, 10 April 2012 (UTC)
thread_title:  Dick Lyon's reversion of an example 

message: As pointed out in this text, this example is a generalization from a a presentation based upon time alone to the case of an analog modulated wave propagating in space as well as varying in time. Personally I see nothing incompatible in this example: it is simply a minor generalization to consider propagation as well a time variation. 
Besides its interest as an academic generalization, this example also is an introduction to similar cases used in phenomena ranging from radar and GPS signals to electronic distance measurement. Brews ohare (talk) 01:44, 7 April 2012 (UTC)
replies: text: Brews, it is perhaps trivial to you that this sort of signed envelope is not at all what an envelope detector detects, nor is it like an analytic envelope, which is a fair description of what an envelope detector attempts to estimate.  Personally, I don't see how this adds to the article, but I'll listen to other opinions.  Dicklyon (talk) 04:39, 7 April 2012 (UTC)
replies: text: Dick: I take your point. Although the subsection Definition of the envelope appears to intend a general discussion of envelopes in AM modulation, in fact it doesn't do this, and in fact, a general definition is not needed for the topic of detection. The article Envelope (waves) should be written instead of redirecting here. Maybe this material would be appropriate there? Brews ohare (talk) 11:56, 7 April 2012 (UTC)
replies: text:  I would suggest Beat (acoustics) as a fitting place for this stuff. Olli Niemitalo (talk) 17:57, 8 April 2012 (UTC)
replies: text: I have placed this material in the new article I've written called Envelope (waves). Brews ohare (talk) 17:01, 10 April 2012 (UTC)
thread_title: References

message: IMHO, the audio section is wrong. Envelope detectors are of use in audio only in the crudest applications, like wah-wah, in which design does not aim at any preservation of the signal ; one seeks any interessant modification of sound. In all other cases, envelope detection in audio must detect both negative and positive, as the signal is not generally symmetrical ; and use AOP+diode, so as to function down to zero amplitude, or alternatively a much shorter time constant in order to approximate quadratic detection. If however the contributor might cite a reference or source, I'd be glad to reform my opinion. PolBr (talk) 08:57, 22 March 2014 (UTC)
replies: text: There are plenty of book sources describing audio envelope followers but it is not clear to me what you think is actually incorrect in the article.  It does not seem to contradict any of the statements you have made. SpinningSpark 11:11, 27 March 2014 (UTC)
thread_title:  Audio 

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thread_title:  External links modified 

message: The red trace of the envelope over the blue signal is misleading, not realizable in real time. The trace of the output of a rectifier is a better, more realistic example of what an envelope is.
12.3.203.132 (talk) 21:42, 8 September 2021 (UTC)
thread_title:  Figure of envelope is misleading