What does line level actually mean and what is the sensitivity setting for? Should I select +4dBu or -10dBV?
Line level is a term used to denote the strength of an audio signal between components such as pre-amps, equalizers, mixers, and amplifiers. Gear offer usually a choice between –10dBV and +4dBu, which raises some questions, the first being, “What do they mean?” immediately followed by “Which do I use?” –10dBV and +4dBu are measures of nominal level. The dictionary defines “nominal” as “the stated or original value only.” In electronics, nominal level is the signal strength at which a 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.