CHAPTER 16 Line Inputs and Outputs 16.1 External Signal Levels 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 +4 dBu and +6 dBu assume balanced outputs which 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 16.1. Signal levels in dBu are expressed with reference to 0 dBu = 775 mV rms; the origin of this odd value is that it gives a power of 1 mW in a purely historical 600 load. Signals in dBv (or dBV) are expressed with reference to 0 dB = 1.000 V rms. These standards are well established, but that does not mean that all equipment uses them as a nominal level. Many power amplifiers require more than 0 dBV for full output; the Yamaha P7000S power amplifier requires +8 dBu (1.95 Vrms) to give its full output of