3080A (+4dB vs -10dB)

[Bob Zimmer]

At 09:16 AM 4/22/96 -0400, you wrote:
>     
>     Somebody else needs to answer the +4dB question because I've totally 
>     forgotten if it's dBm or dBv (my brain is stuck on dBm cuz I work with 
>     lasers all the time).
>

   Here is more detail on an actual answer to the question!

   First, it is important to realize that all voltages mentioned here
   are RMS voltages!

   0 dBu represents 0.775V into a high impedance.  The 'u' stands for
   "unloaded" which refers to the very small load that high-impedance
   circuits exhibit.

   +4 dBm represents 1.228V into 600 ohms.  This is equivalent to the 
   +4 dBu that pro-audio equipment uses!  It is important to remember
   that this level of input would show on a pro recording console or
   tape deck as 0 on the VU meters.

   -10 dBV represents .316V into a high impedance.  This level would
   show on consumer or semi-pro gear as 0 on the VU meters.

   And a quick translation table:

   Semi-Pro        Actual            Pro-Audio
   dBV             Volts RMS         dBm (into 600 ohms or dBu)
    +6.0           2.000                +8.2
    +4.0           1.600                +6.2
    +1.8           1.228                +4.0
     0.0           1.000                +2.2
    -2.2           0.775                 0.0
    -6.0           0.500                -3.8
    -8.2           0.388                -6.0
   -10.0           0.316                -7.8
   -12.0           0.250                -9.8
   -12.2           0.245               -10.0
   -20.0           0.100               -17.8

   This information has been paraphrased from the article
   "Square One: The Wizard of dBs" in the January 1996 issue of
   Electronic Musician Magazine.

   Bob Zimmer

  >=== Bob Zimmer -- Philadelphia PA ===<
  >=== bzimmer at voicenet.com          ===<