Line Level
Although the term refers to the average level of a signal, these days use of the term is more specific and applies to the two line level references, balanced and unbalanced. Balanced or professional equipment operates at +4dBm or 1.23 volts, while unbalanced or semi-professional equipment operates at -10dBV or 0.32 volts. Although the distinction between professional and semi professional equipment is blurring, the important fact is that the two levels should not be speaking to each over. If two pieces of equipment need to be connected that use different line levels, then matching transformers need to be used. Otherwise the +4dBm signal will overdrive an -10dBV input and equally a -10dBV signal will not deliver enough level to a +4dBm input.