What is line level? –10dBV and +4dBu demystified
Line level is a term used to denote the strength of an audio signal used to transmit analog sound information between audio components such as preamps, equalizers, mixers, DVD players, and amplifiers. You’ve probably seen switches on your gear that offer you a choice between –10dBV and +4dBu, which raises some questions, the first being, “What do they mean?” immediately followed by “Which do I use?” Other questions to follow might include “Does one sound better than the other?” and “Can I use a –10dBV unit with one set at +4dBu?”

–10dBV and +4dBu are measures of nominal level. The dictionary defines “nominal” as “the stated or original value only.” In electronics, nominal level is a design specification. It’s the signal strength at which an electronic signal-processing device is designed to operate for optimal performance. The operating level for consumer electronics is –10dBV, while +4dBu is the operating level for professional audio equipment. +4dBu puts out four times the level of –10dBV gear, since professional equipment may require higher voltage levels to carry a signal over longer cable runs without degrading. In properly designed equipment, a –10dBV system will provide equal sound quality to a +4dBu system. Troubles occur when you mismatch settings on interconnected equipment. A +4dBu output will overload a –10dBV input and cause distortion, whereas a –10dBV output will not have enough signal strength to drive a +4dBu input.

The reference voltage for 0dBV is exactly 1.0 volt (1V). –10dBV is equal to 0.316Vrms (rms stands for root-mean-square or continuous voltage). The reference voltage or nominal level of 0dBv is 0.775V, or 1.23Vrms. In dBu, the “u” stands for “unterminated," which originally was referenced by a lower-case “V.” Too often confused with upper-case V, lower case “u” was adopted.

Thank you Bebop,
your information was appreciated. Given that I am very interested but do not have the appropriate technical background I found it most useful.
Keith

Thanks Keith,
I am suprised that not more people were interested in this information. I can still remember when I used to wonder what they were talking about
Best to you,
Bebop

Bebob,

Great post - now I know what those labels mean.

Hammer

Well said.

May I add - and I hope I'm right here - there was a tendency some years ago for some manufacturers to use the term "Professional" to mean "compatible with +4dbu level" signals, and "Home Studio" to mean "compatable with -10dbu level" signals.