XPost: rec.audio.pro, comp.dsp   
   From: dpierce@cartchunk.org   
      
   Don Pearce wrote:   
   > On Mon, 22 Nov 2010 10:58:30 -0500, Dick Pierce   
   >  wrote:   
   >   
   >   
   >>Since energy is power integrated over an interval of time,   
   >>we have all the information we need. The power is whatever   
   >>the scaled sample value is. The interval is 1 sample period.   
   >>Thus the energy is knowable.   
   >   
   >   
   > The sample period is the interval between samples, not the duration   
   > over which a sample is integrated. As far as I know, all ADCs sample   
   > an instant as the edge goes low.   
      
   No, for simple implementation reasons, the aperture,   
   while small, is not zero. It is much smaller than   
   the sample interval, but the fact that is is non-zero   
   leads to a seldom-quoted A/D spec called "aperture   
   error". But, as I mention elswhere, sampling theorom   
   suggests that the difference between an aperture of 0   
   and an aperture approaching a sample width is   
   irrelevant to the resulting data.   
      
   > Energy at an instant is always zero,   
      
   Mr. Einstein muight disagree, given that mass   
   can exist during that same instant.   
      
   > whereas power at an instant is whatever it is.   
      
   But, as you will probably agree, there are no "instants"   
   in any practical system we can build.   
      
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