A line input level electrical signal typically has a voltage ranging from 0,3 to 2 Volts, while a microphone level signal is more often in the range from 5 to 50 mV (millivolts). Microphone sensitivities range from -60 dBu to -22 dBu referenced to 94 dB Soud Pressure Level (0 dB SPL = 2*10–5N/m2). The consumer line input level electrical signal typically has a voltage of 0,32 V (-7,8 dBu), whilst the professional line input level is typically 1,23 V (+4 dBu). For further information see Commonly used Voltage and Audio Levels.
Note: With consumer and semi-professional audio equipment, a VU reading of 0 dB is typically referenced to -10 dBV, which itself is referenced to 0 dBV = 1 V RMS. Professional audio equipment works at a considerably higher level: a 0 VU reading corresponds to +4 dBu. Connecting a professional +4 dBu device to a consumer audio input may produce dangerous overloading, whereas the output of a consumer device probably does not have sufficient power to drive a professional audio input.
Symbol |
Level Definition |
0 dB |
= |
Reference Unit |
||
dBV |
20 * log(Vx/Vref) |
0 dBV |
= |
Vref |
= |
1V |
dBm |
10 * log(Wx/Wref) |
0 dBm |
= |
Wref |
= |
1mW |
dBu |
20 * log(Ux/Uref) |
0 dBu |
= |
Uref |
= |
0.7746V |
dB SPL |
20 * log(px/pref) |
0 dB SPL |
= |
pref |
= |
20µPa |
–10 dBV = 10(–10/20) * 1 V = 0.316 V –7.8 dBu = 10(–7.8/20) * 0.7746 V = 0.316 V 0.7746 V across 600 W: 0.77462 V/600 W = 1 mW +4 dBu = 10(4/10) * 0.7746 V = 1.2276 V Note: dBv = dBu (dBu preferred) all voltage measurements in VRMS |
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Table 5. Commonly used Voltage and Audio Signal Levels and their reference values. Note: 0 dBm = 1 milliwatt which is equivalent to 0,7746 volts RMS into a 600 W load.