From: spam@spam.com   
      
   On Sat, 02 Apr 2011 15:21:55 -0500, flipper  wrote:   
      
   >On Sat, 02 Apr 2011 19:46:54 GMT, spam@spam.com (Don Pearce) wrote:   
   >   
   >>On Sat, 02 Apr 2011 14:38:18 -0500, flipper  wrote:   
   >>   
   >>>On Sat, 2 Apr 2011 02:55:54 -0700 (PDT), Patrick Turner   
   >>> wrote:   
   >>>   
   >>>>On Apr 2, 7:23 am, Newbie  wrote:   
   >>>>> It seems well known that negative feedback can reduce lower order   
   harmonics, but   
   >>>>> increase the higher order ones.   
   >>>>>   
   >>>>> Can anyone direct me to references that show how this happens with   
   mathematical   
   >>>>> analysis?  Perhaps a paper in the journal of the AES, or elsewhere; on   
   the web,   
   >>>>> perhaps?   
   >>>>   
   >>>>   
   >>>>During the last 40 years there have been at least two in depth   
   >>>>articles in Wireless World which later became Electronics World.  I   
   >>>>read all the WW and EW magazines from 1917 to about 1997 and you'll   
   >>>>probably find the articles you want to read if you go where there is   
   >>>>an archived set of the magazines like I did. In about 1993 I spent   
   >>>>days reading in several university library archives to see what had   
   >>>>been said about anything to do with audio engineering. Unfortunately I   
   >>>>don't have copies of all I read, but the phenomena of increasing   
   >>>>distortion spectra after applying NFB is well known, and remains   
   >>>>rivetted into my brain cells.   
   >>>>   
   >>>>The conditions required to "make matters worse" with NFB are about as   
   >>>>follows :-   
   >>>   
   >>>The only condition required to increase higher order harmonics is NFB.   
   >>>   
   >>Negative feedback can never make harmonics worse.   
   >   
   >I didn't say it made "harmonics worse." I said it increases *higher   
   >order* harmonics.   
   >   
      
   Exactly - in terms of harmonics, increasing means making worse.   
      
   >THD decreases because the reduction in low order harmonics is greater   
   >than the increase in high order harmonics.   
   >   
   >> Feedback can make   
   >>harmonics worse when the phase shifts far enough to make it positive.   
   >   
   >That will certainly screw things up but it has nothing to do with the   
   >basic principle of NFB always increasing higher order harmonics.   
   >   
   >Read Baxandall's paper.   
   >   
   I've read it. I suggest you read it again.   
      
   d   
      
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