40
1 dB – smallest audible change in level for an average listener
3 dB – doubling of power
6dB – doubling of sound pressure or voltage
10dB – doubling of perceived level, 20 times the pressure or voltage
40dB – factor of 100 (loudspeaker amplifier with high voltage gain)
60dB – factor of 1000 (microphone or phono amplifier with high voltage gain)
Voltages and decibels
Just like sound waves are rapid pressure oscillations over time, analogue audio signals are rapid voltage
oscillations over time, and the amplitude (level) of an audio signal is described by its voltage, usually an average
over time, or a maximum voltage (peak).
Confusingly, there are two types of decibel used to describe voltages! Both work in the same way, but use
difference reference values. dBu uses 0.775V and dBV uses 1V exactly.
Because these reference values are much larger than the reference value used for dB SPL, we encounter both
positive and negative dB electrical audio signals.
Now we know what decibels are, we can make sense of some of the widely ranging signal levels encountered
in audio engineering:
11.4 Useful dB Increments
VOLTAGES IN DECIBELS
EXAMPLES
dBu
dBV
VOLTS (RMS)
VOLTS (PEAK)
EU mains voltage
+ 49 dBu
+ 47 dBV
230 V
325 V
Maximum line level (professional)
+24 dBu
+21.78 dBV
12.27 V
17.35 V
Hi-Fi DAC
maximum output
+14.25 dBu
+12 dBV
4 V
5.65 V
Line level (professional)
+4 dBu
+1.78 dBV
1.22 V
1.735 V
Reference level dBV
2.21 dBu
0 dBV
1 V
1.41 V
Reference level dBu
0 dBu
-2.21 dBV
0.775 V
1.09 V
Line level (consumer)
-7.78 dBu
-10 dBV
0.316 V
0.445 V
Turntable cartridge (MM)
-43.8 dBu
-46 dBV
0.005 V
0.007 V
Dynamic microphone
-53.6 dBu
-55.9 dBV
0.0016 V
0.0022 V
Turntable cartridge (MC)
-71.7 dBu
-73.9 dBV
0.0002 V
0.000285 V
Self-generated thermal noise of a
10k resistor at room temperature
-112.6 dBu
-114.9 dBV
0.000001816 V
0.00000256 V
