Unused audio output extension cable

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?

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.

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?

On a RealTek HDAudio chip, the "standard" method is jack
side-contact. The "stack" on the back of the computer, can
feel when the plug is inserted and that causes a switch closure.
The standard for 48 pin HDAudio chips, has a scheme whereby
two pins on the package, can sense the status of eight jacks
total. (The switch closures are encoded and sensed by a
crude ADC.)

The RealTek chip does not know whether the load is a 32 ohm
headphone or a 10K ohm audio input from an amplified speaker.
It will put up a dialog asking for confirmation.

A SoundMax HDaudio chip supports two methods. It has the side
contact sensing like all other brands. However, it also has
its own unique method. It applies a 25KHz AC signal to the jacks
to sense current flow (at 25KHz) and work out the impedance of
the load. That product family knows the difference between
a 32 ohm headphone and a 10K ohm amplifier, all by itself.
It could tell if a "remote load" was plugged into the end
of your extension cable.

*******

It seems some RealTek chip in this thread, does now
have a sensor. But the method would have to be different
enough, to not be a patent violation (on the SoundMax method).
Due to the relatively small range of measurements it offers, my suspicion
is they're measuring the current flow used by the output
pad driving LineOut or similar.

https://www.reddit.com/r/audioengine...eeps_changing/

Since they're talking about "output sensing" and not
"I/O sensing", we don't know whether that RealTek also
can sense input types.

*******

When impedance sensing is involved, plugging a headphone
into the remote cable, should be the only time the speakers
are muted.

If a solution only has "side contact detection", then as
soon as the extension cable is plugged in, the speakers
will be muted the whole time. Without actual impedance
measurement, the chip can't tell whether a "remote load"
is present or not.

And even when these techniques are present, the datasheet
may not properly delve into the details.

Some computers do not have the right kind of jacks
with the side-contact on them, in which case "YMMV" :-/

Paul

Bill,

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

Take a look at this image. I think you wil get the idea.

https://www.cui.com/image/getimage/9166

(
https://www.cui.com/blog/understandi...and-schematics )

Regards,
Rudy Wieser

P.s.
It would be a bit more difficult to check if a headphone was plugged into
the /extension cord/ or not. Not that difficult though: it could just put a
small bit of current into the cable (posibly at a frequency below 20 Hz),
and see if it comes back. If not, no headphones.

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

J. P. Gilliver (John) wrote:
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!

AC'97 used two contacts (stereo) in the jack, to direct the
LineOut signals where appropriate. If a headphone was plugged
into the Front Panel headphone jack, the plug would cause the
contacts to open so that the signal could not flow via "FP_Return"
and get to the computer speakers via LineOut jack. This is a
DPDT mechanical switch function.

This allows one DAC to support two jacks. If the front headphones
were not using the signals, then the signals were looped to the
lime green LineOut on the back of the computer.

Whereas HDAudio has enough output channels for everything.
The front headphone jack has its own DAC. There's no need to
share with LineOut. The side contact on the jack, is a
logic indicator. Usage of the front headphones can still
cause the speakers to be muted, but this is a digital
function. In fact, some HDAudio chips, in the driver, support
enabling two headphone amps at the same time, for a total of
four channels of output. This allows two people to listen
to different music feeds (this requires the right kind of
application, like something in the WinAmp class).

The differences between the two schemes are summarized here
in picture form.

https://www.sevenforums.com/sound-au...l-layouts.html

HDAudio has signals for 8 jacks. Headphone and Mic on the front.
7.1 audio out on the back (4 jacks), MicIn, LineIn on the back.
The generic pinout is 48 pins. If a "cheesy" laptop HDAudio chip
is used, a large number of pins are NC. A top end HDAudio chip
uses all the pins and supports the 8 jacks. With AC'97,
fewer jacks were provided, so some multiplexing was needed
here and there.

AC'97 used mechanical switching.

HDAudio uses a single side contact per jack, and that
is a digital logic indication (plug is in/plug is not in).
The driver uses the digital logic indication, to control
which channels are enabled. Classical speaker muting
can be implemented in the driver, using the front
panel headphone jack and its logic indicating signal.

Paul

In message , Paul
writes:
[usual excellent detailed Paul explanation/description]
Paul

Then there's the case of microphone input (often pink), which usually
accepts a three-connection (tip, ring, body) plug, but it isn't
necessarily stereo - the third may be wired to provide the bias voltage
for electret microphones. I had one laptop whose only audio input (_not_
colour-coded) was a microphone one, which presented as stereo in
software, but was mono (same signal appeared on both channels). It
wouldn't surprise me if some systems automatically detect whether what's
plugged in is stereo, mono electret, or mono dynamic (probably rare).
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"Gentlemen, you can't fight in he this is the war room!" (Dr. Strangelove)

J. P. Gilliver (John) wrote:
In message , Paul
writes:
[usual excellent detailed Paul explanation/description]
Paul

Then there's the case of microphone input (often pink), which usually
accepts a three-connection (tip, ring, body) plug, but it isn't
necessarily stereo - the third may be wired to provide the bias voltage
for electret microphones. I had one laptop whose only audio input (_not_
colour-coded) was a microphone one, which presented as stereo in
software, but was mono (same signal appeared on both channels). It
wouldn't surprise me if some systems automatically detect whether what's
plugged in is stereo, mono electret, or mono dynamic (probably rare).

Tip - mono signal in
Ring - electret DC bias
Sleeve - GND

but on the microphone end in that case, they short tip to ring
when an electret is used. Whereas a dynamic (moving coil) mono microphone,
would not touch Ring and would only use Tip. Naturally, some dynamic
microphones predate personal computers and use the "mono" plug design
(tip and sleeve).

or on a stereo setup

Tip - Left Input (AC) plus electret DC bias for this channel
Ring - Right Input (AC) plus electret DC bias for this channel
Sleeve - GND

and in that case, the microphone isn't likely to be a dual dynamic
one. And the amount of current the resistor for the electret provides,
isn't "supposed" to be sufficient to saturate a moving coil. YMMV
of course. It's been a long time since I had a moving coil microphone,
as they need too much gain for computer audio systems to use one.
Like a moving coil on a vinyl record player might only be 2-3mV
or so, and it's a bit much to expect the gain on cheap AC'97
or HDAudio to work with that directly. Nothing prevents more
expensive kit with "preamps" fitted, from doing it.

Carrying electret bias separately, is intended as a means
to give best results with a variety of input types. But they
suspend that notion when dealing with stereo-capable mic jacks.
If you have a dynamic mic with its own amplifier box, the
amplifier has no trouble "pushing around the weak electret
resistor". The amplifier has a low enough output impedance,
to overpower it.

I have more microphones that don't work, versus
microphones that work. The one that works, has a "hard"
power source and has its own four pin preamp chip.
And I can actually dictate with it. There's enough signal.

There seems to be some kind of intent, that your
microphone won't work... :-) I blame the Illuminati.

Paul