dB Vs. dBu
The unit decibel is used because the human ear responds logarithmically to increased sound intensity or power. Units of decibels come in many forms such as dBm, dBW, dBV, dBV and dBFS. The bel is named in honor of Alexander Graham Bell, the inventor of the telephone.
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Main Difference between dBu and dB
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The main difference between the unit dB and dBu is that dB is a power ratio, and dBu is a voltage ratio for an electronic signal.
dB Definition
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The mathematical definition for the decibel as a sound intensity level is given by A = 10log(P2/P1), where P2 is the measured output power. RF (Radio Frequency) engineers usually use 1 milliwatt for the p1 reference level, and their unit is expressed as a dBm, the "m" representing milliwatt.
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dBu
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Voltage is measured easier than power, that is why some people prefer using voltage as a reference. The dBu unit is given by A = 20log(V2/V1). The reference level is 0.775 volts rms. The normal line level dBu rating in audio equipment is 4dBu.
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References
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