[sdiy] doh! (dB talk-talk)

[Tim Ressel]

Quick discussion of dB:

There is always a ***Reference*** to which the dB
number refers to. In the case of 600 ohm balanced
audio, the reference was 1mW into 600 ohms, or
0.775Vrms. The Vrms bit is important. Most dB I've
seen uses RMS. 

First important thing: What is the reference?

Next there is the issue of volts vs. watts. If we are
taling volts, the formula is: 20 * log(V/Vref), and
+6dB doubles the voltage. If we're talking power, then
the formula is: 10 * log(P/Pref), and +3dB doubles the
power.

Second important thing: Volts or Watts?

Up until now I've assumed we were talking dBV, which
is voltage based and referenced to 1Vrms. Clearly that
is incorrect. I have to wonder if there is a standard?
Or are we on our own...

--TR


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