XPost: rec.audio.pro   
   From: spam@spam.com   
      
   On Fri, 19 Nov 2010 19:36:10 -0500, Randy Yates    
   wrote:   
      
   >spam@spam.com (Don Pearce) writes:   
   >   
   >> On Fri, 19 Nov 2010 16:33:53 -0500, Randy Yates    
   >> wrote:   
   >>   
   >>>Hi,   
   >>>   
   >>>Some had responded here to my recent inquiry on levels that dBFS is a   
   >>>peak measurement.   
   >>>   
   >>>If an RMS measurement needs to be made for a digital signal (i.e., on a   
   >>>digital mixing console or a ProTools plugin), what units are utilized? I   
   >>>thought they were dBFS, i.e., that dBFS was an RMS measurement.   
   >>>Apparently I am incorrect. Somebody please set me straight.   
   >>   
   >> dBFS answers the question "by how many dB must the signal be increased   
   >> for the highest peak to hit full scale"? I think that should answer it   
   >> for you.   
   >   
   >No.   
   >   
   >If an RMS measurement needs to be made for a digital signal (i.e., on a   
   >digital mixing console or a ProTools plugin), what units are utilized?   
      
   The problem here is mainly the general one of what an RMS measurement   
   means. With a sine wave it is easy. You can relate the RMS to the   
   peak, which in its turn relates to full scale - the only fixed point   
   with any significance in the digital domain.   
      
   With a music waveform that relationship does not exist in any   
   meaningful way. The only ratio of any practical use is how many dB   
   short of full scale is the largest peak - dBFS in other words. And it   
   isn't a matter of dynamics as in a PPM - it is simply a   
   sample-by-sample assessment. "Have I hit full scale or not?". Of   
   course digital console must be used by people who are accustomed to   
   the analogue domain, and want metering that works in the fashion they   
   are used to. This means the compromise of the PPM or VU meter, which   
   never provides that one vital piece of information.   
      
   As for making an RMS measurement, of course you can always  use the   
   units of volts by relating it back to the ADC or forwards to the DAC.   
      
   d   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)