| The index u at decibel (dB) means unloaded source, V (volt). Some say: The "u" in dBu implies also that the load impedance is unspecified, or unterminated and is likely to be high. The index m at dB (decibel) means 1 milliwatt (power) as reference value for 0 dB. If the reverse conversion dBu, or dBV to volts is needed, go to the converter at the bottom. ● What is dBu? That has nothing to do with power. A logarithmic voltage ratio with a reference voltage of V0= 0.7746 volt ≡ 0 dBu ● What is dBV? A logarithmic voltage ratio with a reference voltage of V0 = 1.0000 volt ≡ 0 dBV The max. domestic recording level of −10 dBV means 0.3162 volts, that is −7.78 dBu
● What is dBm? That has nothing to do with voltage. A logarithmic ratio with a reference power of P0 = 1.000 milliwatt ≡ 0 dBm. The pseudo unit "dBm" is not used in audio and in sound recording. With the known impedance value you can convert voltage V to level dBm (power) and vice versa. Often an impedance of 600 ohms or 50 ohms is assumed. For radio frequency systems (RF), impedance matching or power matching is absolutely essential.
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