Hi,

In message , gecwhite
writes

The twenty comes in because the "voltage dB" is essentially derived from
the "power dB," but power is a non-linear function (square law) of
voltage.

Yes, I got that; I just needed to know which came first :-)

By _Bell System Blue Book definition_:

X(dB) = 10*log(P/P_ref)

*That's* what I was looking for; many thanks. Is the Bell System Blue
book available? Call it sad academic interest.

[Much good stuff snipped to the clipboard for later]

I hope this clears up some of your questions.

All of them. Thanks very much.

--
Regards,
Glenn Booth