Ignore my previous posts about 14dB difference, I was wrong.

After some further reading regarding on the nominal levels of consumer and professional audio, I found some interesting points;

1. The nominal level is a time average of an audio signal, not the peak.
2. For audio, the signal to noise ratio is the difference between the nominal level and the noise floor.
3. The difference between the nominal level and peak signals is the headroom.
4. Consumer nominal level is generally given as 0 Vu = -10dBV (note dBV not dbu)
5. Professional nominal level is 0 Vu = 4dBu
6. dBu is a voltage relative to 0.77459 volts, derived from the voltage required to dissipate 1mW in a 600 ohm load. V = (1mW * 600ohm) ^0.5
7. dBV is a voltage relative to 1 volt.

From the above the following can be derived;

Professional Nominal Level of 4dBu = 1.2276 volts
Consumer Nominal Level of -10dBV = 0.3162 volts
The difference between professional and consumer nominal levels is therefore 3.882 or 11.78dB

Steve.