Archive of the former Yahoo!Groups mailing list: MOTM

A dBu is a voltage measurement, referenced to 0.7746 volts. This ∗magic∗
number is the RMS voltage
across a 600 ohm resistor, dissapating 1 milliwatt.

For a sine, 1V RMS is 2.828V pk-pk.

So, a negative dBu 'reading' means the voltage is ∗less∗ than 0.7746Vrms.

The equation is

dBu = 20 log (Vrms/0.7746)

where Vrms is what you are wanting to measure in dBu's.

To 'go backwards'

Vrms = (.776) (10^dBu/20)

So, -4dBu is 1.38V pk-pk and +22dBu is 27.6V pk-pk! That's about what a
+-15V powered op amp can drive
out 'rail-to'rail', so to speak.

MOTM's 10V pk-pk signal translates to +13.2dBu

Paul S.