49456426   
   XPost: rec.audio.pro, comp.dsp   
   From: gah@ugcs.caltech.edu   
      
   In comp.dsp davew  wrote:   
   (snip)   
      
   > The VU meter is basically a bridge rectifier followed by a low pass   
   > filter.  So it's mean rectified, not mean squared.  So a 1dB   
   > difference for pure tone.   
      
   Well, you can just change the numbers on the scale to represent   
   the squared value.  It is logarithmic (dB) in either case.   
      
   > We don't tend to use rms or mean whatever   
   > when talking about audio levels though, we just say "level" and that   
   > seems to be good enough.  It's understood that when you reach 0dBFS   
   > you're in trouble shortly thereafter.   
      
   In EE, RMS can mean different things.  In some cases, it is   
   the value that a sine would give, with the specified RMS value.   
   That is, for peak-to-peak reading VTVM or mean absolute value   
   reading analog meters, the calibration is for a sine.   
      
   > The only reliable means to know when the limit has been reached is the   
   > peak indicator (and then only if it's true peak which was the subject   
   > of a recent thread or two).  As far as a reasonable measure of   
   > loudness, neither VU or peak or PPM are good enough, just a guide.   
      
   But even with true peak, for live recording it is too late by   
   the time you find the peak.   
      
   > This has all changed no with loudness metering, but that's another   
   > subject.   
      
   -- glen   
      
   --- SoupGate-Win32 v1.05   
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