Re: ALSA sound recording frustration

[John Hasler <jhasler@debian.org>]

lee writes:
> But how do know that there is voltage when you cannot measure it or
> otherwise make evident that there is? As far as I understand it, you
> cannot do that without current flowing. You can do it for water pressure
> without water flowing, but I don't see how you could do it for voltage
> without flow.

 You could use a potentiometer (not the kind you are used to:
 <http://en.wikipedia.org/wiki/Potentiometer_(measuring_instrument)>) or
 you could measure the force exerted on a capacitor plate.  Both these
 methods are used in standards work.  Usually, though, you would just use a
 voltmeter with an input impedence larger that the leakage-resistance of
 the wires connecting it to the source.
-- 
John Hasler