Hi Dave Here is probably more than you ever wanted to know about dBu. It is extracted from the book "Audio Precision Audio Measurement Handbook." Audio Precision is the world's leading manufacturer of precision audio measuring and test equipment. There is also a rather lengthy page discussion on dBm. Let me know by direct e-mail if you want it!
dBu The dBu is a voltage-based decibel unit, referred to 0.7746 Volts. As noted above, 0.7746 Volts is the voltage across a 600 Ohm resistor when dissipating one milliwatt. Thus, dBu and dBm are numerically equal in a 600 Ohm circuit. But, the dBu unit assumes nothing about impedance. dBu is the proper unit to use in most professional audio and broadcasting applications unless it is definitely known that a matched condition exists, and the specific value of termination resistance is known. The audio voltmeters which have been manufactured for many decades are really dBu meters, even though the meter scale or panel switches may be labeled "dBm". These are voltmeters; they cannot measure current, resistance, or power and therefore cannot possibly correctly indicate power. They are calibrated with the assumption of a 600 Ohm circuit (zero dB=0.7746 Volts) and should be labeled dBu meters, but often were produced before the dBu terminology became widespread. dBV The dBV is also a voltage-based unit, referred to 1.000 Volts. It is sometimes used in consumer audio equipment and less-often used in the professional audio and broadcast fields. --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
