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Old March 11th 19, 11:23 PM posted to alt.windows7.general,alt.comp.os.windows-10
Paul[_32_]
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Default Autio input to a PC from bluetooth (or a phone cable?)

micky wrote:
In alt.comp.os.windows-10, on Mon, 11 Mar 2019 13:23:24 +0000, "J. P.
Gilliver (John)" wrote:

In message , micky
writes:
[]
Using the headphone jack gives me the same sort of problem I had when

[]
OTOH, plugging headphones into the headphone jack works just fine. So
is there a problem with the headphone jack or not?

The phone knows what is plugged into the jack, and for some reason it
doesn't like the AUX cable (or what is at the other end) even though
it's happy with the headphones.

This seems to mean I have go back to making bluetooth work. It worked

Or, use a splitter with real headphones (or a resistive load) on the
other arm, so the 'phone _does_ think it is driving 'phones.


Well, believe it or not, even though I'm traveling, had to take a plane,
I actually brought a splitter with me. I didnt' know why, I can't even
remember why I got the thing in the first place.

And it worked!! Well.

Using spare earbuds.

It worked with the PC. I'll try it in the car radio later.

So explain this to me. Don't most people just connect their phone to
the PC or car radio with a simple cable. They don't need a splitter or
earbuds.



(There may be some useful adjustments. Even in win7, in the Sound
window, the Recordig tab, if you right click the microphone jack in use,
and click on Properties, you get Microphone Properties, which has 4
tabs.
General, which identifies which jack it refers to. It says Right
Panel 3.5 mm jack.
Listen, which has a checkbox, Listen to this device, which was not
checked a couple days ago but early on in my reading something said to
check it. It DOES NOT WORK without the check mark. I think this makes
the sound from the mike goes straight to the speakers, or the amplifier,
instead of having to go through a program. Though the label makes that
sound unlikely.
Levels, which allows me to adjust the microphone level so it goes
well with the "mail has arrived" sound etc. And a Microphone Boost
slider which goes in 10db steps. And,
Advanced, which says Select the sample rate and bit depth to be used
when running in shared mode. I don't think I'm in shared mode ???? and
I don't know who I would be sharing what with. So I suppose this
setting does nothing for me???? But it lets one set 16 bit or 24 bit (I
have know idea which I want, but it's working well now with 16-bit,
44100Hz, CD quality.) And it has 6 possible frequencies for 16 bit,
44100 CD quality, 48000 DVD quality and 88200, 96000, 176400, and
192000 which are all studio quality.


One of the audio capabilities in PC audio, is to loop
the material being played to the speakers, back to an
ADC on the input side. This is termed "What You Hear"
or "Stereo Mix". On Win10, this is a "Disabled" item, and
Microsoft makes you bob for apples to find it and switch
it on. It's considered a DRM-thwarting path, which is
why the bums switch it off and try to hide it.

Line-In ---
\
Mic-In --- -- ADC DAC ---+-- (Amp)--- LineOut
/ |
Stereo Mix +-- |
| |
+---------------------------+

That shouldn't be a useful option in your current situation,
as you are taking audio from another input side source
(Mic In or Line In) and playing that to speakers.

As for the device sensing and operational adjustments
the phone is making, I don't know what capabilities they
think they have on phones.

*******

On PC audio, you can attempt to sense the difference
between a "Line Level Input", which has a defacto
standard input impedance of 10K ohms. Or the other
option is 32 ohm headphones. Sound chips have a power
amp on the output, which is "switchable". If a 32 ohm
headset is detected, a CMOS power amp drives that. And
puts up to 1V amplitude on it. The power amp has a
roughly 1 ohm output impedance (it is "stiff" in
electronics parlance, and is a "voltage source"
or close to it). Because the value is finite, it
implies there isn't closed loop feedback around
the power stage, to make the effective impedance
even lower.

Now, what we don't know, is the overload behavior
of that amplification stage. It's known that the
amplification stage, when used, degrades the SNR by
10dB. So it's not always the best choice for audiophile
recording purposes. But you do get the benefit of
higher drive, if you tell a device "drive my headphones".

The other case, is with the amplifier stage switched off.
Well, there's still an amplifier, but it's around 600 ohm
drive. A 600 ohm, line level (1volt) output, still
nicely drives a 10K input on another piece of stereo
recording equipment or drives the Line In on the computer.

When driving Zalman 5.1 headphones, there are like
six speakers inside the oversized headphones. This
requires three stereo pairs of amps at 32 ohms.
What happens is, if you plug those into an HDAudio
on a computer (three 1/8" plugs), the FrontLeft/FrontRight
work fine at 32 ohms. However, the other four channels
of sound won't switch on their amps. The other four channels
are driven at 600 ohms, and the channels in question
are "weak" and you can barely hear them. What we
learn from this, is the sound chip is not willing
to switch on the amps on *all* channels, even if
it happens to sense that they need it.

How many weird sounds can you get from audio equipment ?

Well, there's the "motor boat sound", a kind of put-put-put
that comes from an overloaded op-amp. Typically this comes
from driving a pure capacitive load, without a series
resistor between the opamp and capacitor, to "adjust"
the closed loop behavior of the amplifying circuit.
The outputs on computer sound, are capacitively coupled,
but that is a *series* capacitor, not a capacitor to ground.
However, if you connect a heavy enough load (a short
circuit to ground), then the series capacitor is now
a parallel capacitor to ground. And it would be
expected that the output would make the put-put sound.

That's the only behavior I know of, that makes a peculiar
sound effect. The effect might range from, say, 1Hz to 100Hz.

One of my fellow engineers discovered this one day,
and said "hey, come over and look at this".
And I took a look at his schematic, and see this
big-ass capacitor to ground, on the output of an
opamp. And my response was "you can't do that...".
And dug up an applications note, with the proposed
solution to moving the resulting pole so that
the closed loop wouldn't oscillate. I have fallen
into this "moar capacitor equals better performance"
trap my own self, as a hobbyist, and that's why I
knew what to look for :-/ The best learning
is from your own train wrecks.

Just about every audio amp circuit I ever built,
oscillated, with the most comical one being the
amp that oscillated at 500KHz and I could only
see it on an oscilloscope at school (i.e. you can't hear it,
but you can tell something is wrong because the
amp sounds "weird" and "hollow").

Paul
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