XPost: rec.music.gdead, sci.electronics.design   
   From: SaySooth@TheMonastery.org   
      
   On Fri, 04 Mar 2011 08:55:23 +0100, Jeroen Belleman   
    wrote:   
      
   >SoothSayer wrote:   
   >> [...]   You have to MODULATE the AMPLITUDE of a   
   >> "carrier" with the intended "signal"..   
   >>   
   >>   Simply seeing something that appears to be "enveloped" does not mean   
   >> that it is amplitude modulated. Linear summation does not get you there.   
   >   
   >Time for a trigonometry refresher course:   
      
    Are you sure?  Could it be semantics?   
   >   
   >Modulation is multiplication of two signals, e.g., for sine waves   
   >cos A * cos B.   
      
     Funny, I thought modulation was using one signal to control the   
   amplitude of another signal.   
      
   Multiplication?   
      
   >   
   >A basic trigonometric identity tells us this is identical to:   
   >0.5 cos(A+B) - 0.5 cos(A-B), which is a simple linear sum of   
   >sine waves.   
      
     Is it identical?  Are you saying "sum" or "multiply"?  They are   
   different words.  You should choose one.   
   >   
   >In conclusion, your assertion that linear summation can't   
   >get you a modulated waveform is wrong.   
   >   
     The 'waveform' is not what is required to be modulated to qualify as   
   AM.  The amplitude of a carrier has to be modulated by the second signal.   
      
     Simple summation of the two signals is a summated pair of sine waves.   
   Shows up a little different on the scope. Besides, you said multiply, not   
   sum.  So, two tens gets you a hundred?   
      
     Modulating the amplitude of one sine wave with the other is a different   
   injection method.  Two tens will get you twenty.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)