# Talk:Prototype filter

this fomula is not really clear to me, as to how it is implemented.

  
    
      
        i
        ω
        →
        
          (
          
            
              
                ω
                
                  c
                
                ′
              
              
                ω
                
                  c
                
              
            
          
          )
        
        i
        ω
      
    
    {\displaystyle i\omega \to \left({\frac {\omega _{c}'}{\omega _{c}}}\right)i\omega }
  

Maybe you mean

  
    
      
        i
        
          ω
          
            n
          
        
        
          =
        
        
          (
          
            
              
                ω
                
                  c
                
                ′
              
              
                ω
                
                  c
                
              
            
          
          )
        
        i
        
          ω
          
            o
          
        
      
    
    {\displaystyle i\omega _{n}{=}\left({\frac {\omega _{c}'}{\omega _{c}}}\right)i\omega _{o}}
  

where the o is the old value and the n is the new value?
Is this how it is used?  An example of the use of each formula would be nice, or at least an example of the first few formulas....
Baruchatta (talk) 15:57, 17 November 2009 (UTC)

Agreed. I assume that "i" is the imaginary number described in https://en.wikipedia.org/wiki/Imaginary_number , and thus just a book-keeping notation, and I similarly assume that "w" is either a generic placeholder (in which case I question why the common "x" wasn't used instead) or denotes a frequency in radians, but none of these things are actually mentioned. The article is fairly nice, but it's internal notation is insufficiently documented. 2602:301:7764:AC00:2107:543D:AD78:5200 (talk) 07:31, 30 March 2022 (UTC)
The symbol 
  
    
      
        ω
      
    
    {\displaystyle \omega }
  
 is a lowercase omega, not a w.  This is the usual, widely used, symbol for angular frequency and is defined as such earlier in the page, but admittedly only with respect to a specific frequency with a subscript.  It is written in that form because the transfer functions of passive filters are always a rational function of 
  
    
      
        i
        ω
      
    
    {\displaystyle i\omega }
  
.  Now the 
  
    
      
        i
      
    
    {\displaystyle i}
  
 can be cancelled out in this case, but it can't in the more complex transformations discussed later in the article so I left it in for consistency.  The transfomation is applied by replacing 
  
    
      
        i
        ω
      
    
    {\displaystyle i\omega }
  
 with the transform everywher it appears in the transfer function.  Likewise, the components of the filter can be determined by making the same transformation to the expression for the impedance of the component. SpinningSpark 08:40, 30 March 2022 (UTC)

This review is transcluded from Talk:Prototype filter/GA1. The edit link for this section can be used to add comments to the review.
Reviewer: Brambleclawx 18:07, 28 July 2010 (UTC)
I will now review this for GA status.
This article does not meet criteria for "quick-fail", so I will now conduct a full review. I may have to put this on hold at some point in case I do not understand the more technical/mathematical sections.


### Comments
1a.: The prose could do with a bit of work. I will try to sort that out tomorrow. Also, the advanced mathematics make me feel out of my comfort zone.

In the section "Alternative prototype", the paragraph "With image filters..." contains a sentence fragment that I don't know how to fix: "Constant k being those filters for which Z/Y is a constant." Could you please correct this?
You will need to explain to me what you want to fix.  Constant k is introduced for the first time in the previous sentence.  The sentence under discussion clarifies this by defining the meaning of constant k.  The two sentences could be run together with a comma - would that solve your problem? SpinningSpark 19:36, 30 July 2010 (UTC)
I believe so. Brambleclawx 19:58, 30 July 2010 (UTC)
3a.: The article's references are well written, but now, I'd like to point out that while you've explained what a prototype filter is and how it works, you have not mentioned examples of where they are used. Brambleclawx 22:42, 14 August 2010 (UTC)

I am not at all sure that examples are meaningful here.  The prototype filter is a design tool, not an end product.  Any (linear) filter design in any application at all can make use of prototypes.  Of course, any number of applications for filters (which are very numerous) could be mentioned, but this would be a bit contrived, none of them would actually be prototype filters, we could only say that the designer might have used protoypes in producing them.  The article does give specific examples in the figures of transformed filters. SpinningSpark 10:27, 15 August 2010 (UTC)
Oh. I get it. Thanks. Brambleclawx 15:44, 16 August 2010 (UTC)
GA review (see here for criteria)
It is reasonably well written.
a (prose):  b (MoS): 
Prose is ok now, MoS looks good.
It is factually accurate and verifiable.
a (references):  b (citations to reliable sources):  c (OR): 
This looks okay as well.
It is broad in its coverage.
a (major aspects):  b (focused): 
Good.
It follows the neutral point of view policy.
Fair representation without bias: 
Neutral, good.
It is stable.
No edit wars, etc.: 
Stable, no edit wars evident
It is illustrated by images, where possible and appropriate.
a (images are tagged and non-free images have fair use rationales):  b (appropriate use with suitable captions): 

Overall:
Pass/Fail: 

I am glad to pass this article, which meets all the GA criteria. Brambleclawx 20:58, 26 August 2010 (UTC)
The article's prose is fairly well written, and the images help illustrate the article well. The only thing I have not checked is whether or not the formulae are correct, but I assume they are. Brambleclawx 21:00, 26 August 2010 (UTC)