ABSTRACT
There are several standards for line signal levels. The 10 dBv standard is used for a lot of semi-professional recording equipment as it gives more headroom with unbalanced
connections – the professional levels of þ4 and þ6 dBu assume balanced outputs that inherently give twice the output level for the same supply rails as it is measured between two
pins with signals of opposite phase on them. See Table 14.1
Signal levels in dBu are expressed with reference to 0 dBu ¼ 775 mVrms; the origin of this odd value is that it gives a power of 1 mW in a purely historical 600 U load. The unit of dBm refers to the same level but takes the power rather than the voltage as the reference – a
distinction of little interest nowadays. Signals in dBv (or dBV) are expressed with reference
to 0 dB ¼ 1.000 Vrms. These standards are well established, but that does not mean all equipment follows them. To
take a current example, the Yamaha P7000S power amplifier requires þ8 dBu (1.95 Vrms) to give its full output of 750 W into 8 U.
