[techtalk] strange unknown...
johngalt at io.com
Wed Sep 27 02:09:52 EST 2000
Hardly a simplistic response, Stephanie. So many of us are accustomed to
having kernel problems and what not, that the simple things elude
us. However, I don't think that that is the case here.
Betka, do you experience anything out of the ordinary besides the
sound? Is the sound coming out of your speakers that are plugged into the
sound card, or out of the PC speaker mounted on the chassis?
If the answer to the first one is: yes, I'm experienceing random
characters and whatnot on the screen...then Stephanie is probably correct.
If the answer to the second is: the speakers used with the sound card,
maybe we can isolate the problem by doing this...
Does the noise happen if you plug the speakers into something else
(headphone jack on a boombox, etc)? If so, it is the speaker.
Does the noise happen in a different location? You could be getting some
sort of disturbance that isaffecting the audio (doubtful)
Can you try a different power-adapter for the speakers? Maybe run them
off of batteries? This is a very likely cause. The power coming out of
your wall is AC. It has a 60Hz frequency (assuming you're in the
US). Your speakers, however, run on DC...that's why you have an adapter
to supply them with power. It may be that your adapter is broken.
The only other thing I can think of is something in the kernel driver that
would do it...but if it does it when you're sitting idle....I suspect it's
hardware, and I suspect it's the speakers.
That should be a start. Now, for a technical explanation of why the last
reason might cause the "dadadada" sound. Feel free to skip this if you
don't want to get into the electronics of it. The above troubleshooting
should isolate the problem.
This really goes into three topics: AC/DC conversion, the mechanics of a
speaker, and fundamentals of acoustics.
First I'll address AC/DC conversion. When Thomas Edison and Alexander
Graham Bell and all of their cohorts were making electrical gadgets they
were using direct current (DC). Direct current only flows one
direction. If you look at it on an oscilloscope it is a straight
line. A great deal of modern electronics utilizes DC to achieve its
goals. This is how logic circuits (and thus your
computer) work. Alternating current (AC), on the other hand, was
pioneered around the turn of the turn of the century by a man named Nikola
Tesla. (Begin short plug for my favorite historical figure.) He designed
the AC dynamo that made Westinghouse famous. Tesla also designed the AC
generators that run at Niagara falls (beating Edison out for the
deal). AC is different from DC, in that it changes the direction it
travels. In a regular alternation it goes to the left, and then to the
right. Another way to think of it, is that the voltage changes from
positive to negative and back in a never ending cycle. When you look at
AC on an ocilloscope, you get something that looks like a sine wave.
One of the shortcomings of DC is that it cannot travel very great
distances without losing a lot of its electron moving oomph (voltage or
electromotive force). AC is much better at traveling long
distances. However, AC is not good for most delicate circuitry. So...we
can transport with AC, but need to convert to DC.
How do we do this? Through a gizmo called a diode. A diode is a nifty
little gizmo that only lets current flow through it in one direction. So
when the AC switches directions, it doesn't flow back through the
diode. But when it changes again, it goes through the diode again.
If you picture AC as a sine wave, and draw a line along the x axis (where
sin(x)=0), then chop off everything below the line. You end up with
bumps and spaces. If you did the same thing to some alternating current,
the flow of current would come in pulses. (Remember this, I'll come back
to it later). These pulses are not desirable, so we have to figure out a
way to make the current a steady stream.
Enter another nifty gizmo: the capacitor. The capacitor stores
electrons (it stores electricity). While this doesn't sound like a really
spectacular thing, it does serve a nifty purpose. If you place a
capacitor in the circuit right after the diode, it will suck up the
electrons until it is full...but then it will discharge the electrons when
there aren't any. Basically, it fills in where the empty spots are,
making it a continuous stream. A good analogy is a balloon and a water
pipe. The baloon is attatched to the side of a water pipe (it's a really
strong rubber baloon)...now when the water first starts flowing, it fills
up the balloon. Then, when the water stops, what is in the baloon comes
out. If the balloon is the correct size so that it holds enough water to
fill in the gaps between spurts, it creates a continuous stream of water.
That's how AC-DC conversion works.
Next, acoustics. This is just really basic sound physics. Sound is
vibration. Something vibrates, this makes the air molecules
vibrate...they vibrate the molecules next to them, and it gets to your ear
and vibrates your eardrum...etc. Sound is vibration. Without a medium to
vibrate in, there is no sound. Simple enough.
A speaker uses electromagnetism to vibrate. If you've ever taken one
apart, you'll notice there is a great big huge magnet on the back. Wires
are run into a coil in the little button in the middle of your speaker (if
you look closely, you'll see what I mean). When electricity is passed
through this coil, it generates a magnetic field. This attracts the
button (at the base of the speaker cone) to the magnet. If you turn the
electricity on and off really quickly, this will cause the cone to
vibrate. Making, you got it!, sound. Now what you do is vary the speed
at which the electricity pulses through the coil to vary the frequency of
vibration. The faster it vibrates, the higher pitch it makes. Now the
current used to do this comes from the wire that plugs into your sound
card...not your AC adapter...however...the power coming into the unit to
run things is used to amplify the signal coming from your sound card.
I'm sure you've all already figured out where all this background science
If the capacitor in the AC/DC converter for your speakers is shot, then
the speakers recieve their power in pulses (at a frequency of 60Hz...or 60
pulses/second). When this current is used to amplify the signal from the
sound card, the 60Hz pulse gets injected along with it. This can manifest
as a "da da da da da da" sound...fitting 60 "da"'s in a second.
I hope that that educated some people!
What a doozy for my first post, goodness, I really got away with myself.
Anywho...try all those troubleshooting steps I suggested, and if it still
gives you problems, let me know.
Penguins are good luck!
On Tue, 26 Sep 2000 stephanie1200 at netscape.net wrote:
> please don't smack me for such a simplistic response but, you don't have anything goofy lying around like a mouse cable or something that would rest on a key under certain conditions? Like is your keyboard in a rack that would bump into a key or something? stuff like that has happened to me lots of times. just the other day i brought down a solaris box because the keyboard cable hit the suspend key as I was sliding it back into the rack drawer... oops...
> betka <betka at courtade.net> wrote:
> > hiyis...
> > i have this sound that my machine makes...
> > kinda goes dadadadaadaaa
> > we can not figure out what is doing it
> > no specific time of day ....completely random
> > have changed sound cards
> > nothing ever appears in the logs
> > i am running red hat 6.2 .. but this has accured through several
> > upgrades
> > it also happens even when the sound card is in use (as in real audio)
> > anyone ever have this happen or have any ideas to why it is happening?
> > ta
> > betka
> techtalk mailing list
> techtalk at linuxchix.org
Sam Lavenz -- KC0BUH
johngalt at io.com
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freedom and to take no part in a slave society"
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