Chapter 20

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 20.1.

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. Signals in dBv (or dBV) are expressed with reference to 0 dB = 1.000 Vrms.

These standards are well established, but that ...

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