[William Sommerwerck]

"Sean Conolly" wrote in message ...

But if we sum equal levels of random noise, I'd guess at any given
moment you'd have slightly less than 3dB, but when averaged over
time the signals are would still would add 3db when summed.

If they were always "slightly less than 3dB", then they could never be 3dB
over the long term.