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**J. P. Gilliver (John)[_7_]** · September 10th 19, 11:07 PM posted to microsoft.public.windowsxp.general

In message ,
writes:
On Tue, 10 Sep 2019 11:10:53 -0400, BillAhearn
wrote:

How does the operating system know that an audio cable extension is plugged
in?

I have a 20 foot audio extension cable which is just male on one end and
female on the other.

If I plug in a headphone into that extension cable the sound comes out the
headphones and not out the computer speakers.

When I just plug in the extension cable, the sound stops coming out of the
speakers.

How does the OS know that an (unused) audio cable is plugged in?

It monitors the impedance of the output or input.

Impedance checking wouldn't work with nothing plugged into the other end
of the cable. (Well, very clever impedance checking might, of the sort
used for finding where the break is in a cable, but not the sort I'd
expect in computer audio circuitry.)

It's probably a switch in the socket that detects something being
plugged in - probably detected by the audio chip and switched
electronically, as described by Paul, but it _could_ be just the
mechanical type of switch as described by Rudy - in the same way
headphone/earphone sockets have muted the speaker on plugging in the
headphone/earphone (or anything else) since at least 1960s transistor
radios, probably longer ago. No OS intervention needed!
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

The motto of the Royal Society is: 'Take nobody's word for it'. Scepticism has
value. - Brian Cox, RT 2015/3/14-20