XPost: rec.audio.pro   
   From: mrivers@d-and-d.com   
      
   On 11/19/2010 10:09 AM, Randy Yates wrote:   
      
   > What I meant to ask is if   
   > there is a standard way to map the full-scale output of a DAC   
   > (or input of an ADC) to a specific voltage voltage level.   
      
   Nope.   
      
   >> There are a few conventions, however, but mostly there's things that   
   >> you choose for yourself, not a standard to which a manufacturer   
   >> adheres. Back when people had VU meters and digital recorders had   
   >> readable meter scales and an adjustable input level control, there was   
   >> often a mark typically somewhere between -16 and -20 dBFS on the   
   >> digital meter that was the recommended point corresponding to 0 VU.   
   >   
   > And 0 VU correspondings to +4dBu?   
      
   Another point of great confusion. 0 VU is whatever nominal   
   operating level is. On "pro" equipment, it's usually +4 dBu.   
   On "semi-pro" equipment, it's usually -10 dBV. On some phone   
   company, it's +8 dBm (a unit of power, not voltage, but   
   usually into 600 ohms, so you can calculate the voltage). On   
   a consumer tape deck, who the heck knows? Usually somewhere   
   around -20 dBu.   
      
   > That's the same translation Paul mentioned: +4dBu = -20 dBFS.   
      
   Yup, he's a smart feller.   
      
   > No one has yet answered the question about whether it's FS sine   
   > or FS square.   
      
   It doesn't really matter until you want to find the RMS   
   value of the waveform that got you to that digital level. If   
   0dBFS = +24 dBu, either a square wave or a sine wave with   
   the same peak value will get you there.   
      
   The RMS value of a sine wave is 0.707 (1/2 the square root   
   of 2) times the peak amplitude. The RMS value of a square   
   wave is the same as the peak amplitude.   
      
      
      
   --   
   "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   
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