CHAPTER 18
Line Inputs
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 18.1.
Signal levels in dBu are expressed with reference to 0 dBu = 775 mVrms; the origin of this odd value is that it gives a power of 1 mW in a purely historical 600 Ω load. The unit of dBm refers to the same level but takes the power in the load rather than the voltage as the reference– ...
