XPost: rec.audio.pro, comp.dsp   
   From: mrivers@d-and-d.com   
      
   On 11/19/2010 7:52 PM, Randy Yates wrote:   
      
   > My question is this: What is the definition of dBFS?   
      
   Decibels relative to full scale. 0 dBFS is full scale,   
   everything else is down from there. -6 dBFS is half the   
   maximum number as with all the bits on.   
      
   > If dBFS is defined as   
   >   
   >    dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave),   
   >   
   > where XRMS is the RMS value of the digital data stream, and you're   
   > generating a "digital square wave," then you are wrong. The digital   
   > square wave can go to +3dBFS as defined above.   
      
   But it's not defined that way. In reality, you can't have   
   anything higher than 0 dBFS. That's where you run out of   
   numbers to express the amplitude. There's such a thing as   
   "intersample overload" where the input actually goes higher   
   than the 0 dBFS level between two adjacent samples, but   
   that's an anomaly.   
      
   > It seems that there really is no standard definition. That's the   
   > problem. It's not a matter of abstractness, but rather of   
   > well-definedness.   
      
   The thing is that what you're concerned with in digital   
   recording is how much headroom you have. You can choose your   
   own headroom amount simply by choosing the analog reference   
   level that gives your desired headroom. If you're   
   compressing the piss out of everything, you don't need as   
   much headroom as if you're recording an orchestra or   
   something where you're unsure of the input dynamic range,   
   and you can choose a higher reference level. For most music,   
   20 dB of headroom is pretty safe, which is why the -20 dBFS   
   reference is fairly common.   
      
      
   --   
   "Today's production equipment is IT based and cannot be   
   operated without a passing knowledge of computing, although   
   it seems that it can be operated without a passing knowledge   
   of audio." - John Watkinson   
      
   http://mikeriversaudio.wordpress.com - useful and   
   interesting audio stuff   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)