sorry, ill try to be more clear.

will the audio signal only ever go into clipping if you exceed 0db on the output volume?

reason i was asking about voltages is i know with my amps (fusion monoblocks) the audio signal will clip as soon as the output voltage reaches 60v (so i dont need to wire them to a scope to see if they are clipping, i just set the output to 59v).

i was therefore assuming that the head unit audio output would work in the same way - as the volume rises so too would the voltage of the signal. i didnt realise it was a constant 4v.