# Re: ALSA sound recording frustration

```On Thu, Nov 27, 2008 at 09:11:31PM -0500, Napoleon wrote:
> lee wrote:
>> On Thu, Nov 27, 2008 at 07:06:42PM +0200, Rob de Graaf wrote:
>>> An input which measures voltages (here the microphone input) has
>>> infinite large impedance, hence no current will flow.
>> How can there be voltage (or voltage measured) without current
>> flowing?
>>
>>
>> http://en.wikipedia.org/wiki/Volt:
>>
>> "The volt is defined as the potential difference across a conductor
>> when a current of one ampere dissipates one watt of power."
>
> The wikipedia article is correct as to the definition of a volt in
> mathematical terms.  However, voltage is the electrical equivalent of
> water pressure.  You can have water pressure, even if there is no water
> flowing (i.e. a full water tower with no water flowing out).

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 still have a voltage across a battery, even when no current is
> flowing.  And you still have voltage at your outlet, even though no
> current is flowing.

How do you know?

> Without getting into the more technical stuff, for correct operation
> impedances need to match.  Any mismatch lower performance.  A small
> mismatch probably won't be noticed but a larger one will.

Yes, what you're explaining is pretty much the point: It's not a good
idea to connect incompatible things like a headphone outlet to a
microphone inlet without appropriate adaptation. It might work or not,
it might damage something or not ...

--
"Don't let them, daddy. Don't let the stars run down."