how does an audio signal work?

When I plug headphones into an ipod, I know that electricity of some kind
flows through the wire into the headphones, producing sound. What I don't
understand is, what exactly is done to the electricity to make an audible
signal?

I'm pretty sure the ipod controls the volume by changing the amplitude. If
you put a variable resistor between the ipod and the headphones, you can
reduce the volume. How does the ipod control the pitch of the sound? Does
it change the voltage, or the frequency (turning it rapidly on and off), or
what?

 

[Speeders & Drunk Drivers]

<unknown.hero@aa.ee> wrote in message news:ha1bna$gv8$1@aioe.org...

When I plug headphones into an ipod, I know that electricity of some kind
flows through the wire into the headphones, producing sound. What I don't
understand is, what exactly is done to the electricity to make an audible
signal?

I'm pretty sure the ipod controls the volume by changing the amplitude. If
you put a variable resistor between the ipod and the headphones, you can
reduce the volume. How does the ipod control the pitch of the sound? Does
it change the voltage, or the frequency (turning it rapidly on and off), or
what?

Your English is much better than mine, but why you got such a shitty brain? Oops! sorry human, I learn your language, I'm an alien from other planets. The electricity in a form of voltage(/amplitude) shakes the diaphragm of your speaker, this is what makes noise for your lousy ears.

http://www.simplyspeakers.com/12diaphragms.htm

A resistor does not change the frequency, it minimizes the amplitude of a signal(waveform),

 

[BobW]

<unknown.hero@aa.ee> wrote in message news:ha1bna$gv8$1@aioe.org...

When I plug headphones into an ipod, I know that electricity of some kind
flows through the wire into the headphones, producing sound. What I don't
understand is, what exactly is done to the electricity to make an audible
signal?

I'm pretty sure the ipod controls the volume by changing the amplitude.
If
you put a variable resistor between the ipod and the headphones, you can
reduce the volume. How does the ipod control the pitch of the sound?
Does
it change the voltage, or the frequency (turning it rapidly on and off),
or
what?

Without going through all the interim steps, the basic concept is that the
voltage coming out of the iPod (at any given volume control setting) is an
'analog' of the original vibrations of the source of the music.

Let's say that you're listening to somebody who was whistling into a
microphone, and let's also say that the person was whistling a pitch that
was a pure and simple sound (aka a sinusoid), and let's also say that the
whistling was vibrating the air (and microphone diaphram) 422 times per
second.

The voltage coming out of your iPod will be vibrating at the same rate, that
is at 422 times per second. When this vibrating voltage is then applied to
your headphones (because they're plugged into your iPod) then the
headphone's voice coil and diaphram will be shaking back and forth 422 times
per second.

If you turn down the volume control on the iPod, or add resistance between
the iPod and headphone's wires, then the magnitude of the voltage vibrations
at your headphones will be reduced, but the rate at which the voltage is
vibrating is still 422 times per second.

The key thing to note is that the 'shape' or 'pattern' that the vibrations
take will always be similar, or an analog, of the vibrations of the original
whistler's microphone's diaphram. The relative size of these vibrations will
vary depending on the setting of the volume control, but the shape of the
vibrations will still be similar or analagous to the original whistle.

So, in a nutshell, the iPod does not directly control the frequency of what
is fed to your headphones. It only is changing the voltage to the headphones
in an attempt to maintain a similar looking pattern/shape/analog between
that which has been recorded and the voltage to the headphones.

If you want a more detailed explanation of how the entire process works
(i.e. analog-to-digital conversion, digital storage, digital-to-analog
conversion) then you'll need to do a lot of reading.

Bob
--
== All google group posts are automatically deleted due to spam ==

 

BobW wrote:

Without going through all the interim steps, the basic concept is that the
voltage coming out of the iPod (at any given volume control setting) is an
'analog' of the original vibrations of the source of the music.

Let's say that you're listening to somebody who was whistling into a
microphone, and let's also say that the person was whistling a pitch that
was a pure and simple sound (aka a sinusoid), and let's also say that the
whistling was vibrating the air (and microphone diaphram) 422 times per
second.

The voltage coming out of your iPod will be vibrating at the same rate,
that is at 422 times per second. When this vibrating voltage is then
applied to your headphones (because they're plugged into your iPod) then
the headphone's voice coil and diaphram will be shaking back and forth 422
times per second.

If you turn down the volume control on the iPod, or add resistance between
the iPod and headphone's wires, then the magnitude of the voltage
vibrations at your headphones will be reduced, but the rate at which the
voltage is vibrating is still 422 times per second.

The key thing to note is that the 'shape' or 'pattern' that the vibrations
take will always be similar, or an analog, of the vibrations of the
original whistler's microphone's diaphram. The relative size of these
vibrations will vary depending on the setting of the volume control, but
the shape of the vibrations will still be similar or analagous to the
original whistle.

So, in a nutshell, the iPod does not directly control the frequency of
what is fed to your headphones. It only is changing the voltage to the
headphones in an attempt to maintain a similar looking
pattern/shape/analog between that which has been recorded and the voltage
to the headphones.

If you want a more detailed explanation of how the entire process works
(i.e. analog-to-digital conversion, digital storage, digital-to-analog
conversion) then you'll need to do a lot of reading.

Bob

What is a "vibrating voltage"? Does that mean that, in your example, the
voltage is turning on and off or changing directions at 422 times per
second?

What exactly does it mean for voltage to "vibrate"?

Thanks for your time.

 

[Tim Wescott]

On Wed, 30 Sep 2009 22:45:59 -0700, unknown.hero wrote:

BobW wrote:
Without going through all the interim steps, the basic concept is that
the voltage coming out of the iPod (at any given volume control
setting) is an 'analog' of the original vibrations of the source of the
music.

Let's say that you're listening to somebody who was whistling into a
microphone, and let's also say that the person was whistling a pitch
that was a pure and simple sound (aka a sinusoid), and let's also say
that the whistling was vibrating the air (and microphone diaphram) 422
times per second.

The voltage coming out of your iPod will be vibrating at the same rate,
that is at 422 times per second. When this vibrating voltage is then
applied to your headphones (because they're plugged into your iPod)
then the headphone's voice coil and diaphram will be shaking back and
forth 422 times per second.

If you turn down the volume control on the iPod, or add resistance
between the iPod and headphone's wires, then the magnitude of the
voltage vibrations at your headphones will be reduced, but the rate at
which the voltage is vibrating is still 422 times per second.

The key thing to note is that the 'shape' or 'pattern' that the
vibrations take will always be similar, or an analog, of the vibrations
of the original whistler's microphone's diaphram. The relative size of
these vibrations will vary depending on the setting of the volume
control, but the shape of the vibrations will still be similar or
analagous to the original whistle.

So, in a nutshell, the iPod does not directly control the frequency of
what is fed to your headphones. It only is changing the voltage to the
headphones in an attempt to maintain a similar looking
pattern/shape/analog between that which has been recorded and the
voltage to the headphones.

If you want a more detailed explanation of how the entire process works
(i.e. analog-to-digital conversion, digital storage, digital-to-analog
conversion) then you'll need to do a lot of reading.

Bob

What is a "vibrating voltage"? Does that mean that, in your example,
the voltage is turning on and off or changing directions at 422 times
per second?

What exactly does it mean for voltage to "vibrate"?

Thanks for your time.

What does it mean for anything to "vibrate"?

Saying that the voltage in an audio signal is "going on and off" is true
in a sophomoric sense, but seriously misrepresents the important parts of
what is happening.

A signal at 422Hz would be going up 422 times per second, and going down
422 times per second.

--
http://www.wescottdesign.com

 

[Tim Wescott]

On Wed, 30 Sep 2009 21:38:22 -0700, unknown.hero wrote:

When I plug headphones into an ipod, I know that electricity of some
kind flows through the wire into the headphones, producing sound. What
I don't understand is, what exactly is done to the electricity to make
an audible signal?

I'm pretty sure the ipod controls the volume by changing the amplitude.
If you put a variable resistor between the ipod and the headphones, you
can reduce the volume. How does the ipod control the pitch of the
sound? Does it change the voltage, or the frequency (turning it rapidly
on and off), or what?

This is kinda what BobW said, only hopefully simpler:

What is done to the electricity to make an audible signal is to make a
voltage that varies the same way as the sound pressure needs to vary at
the output of the speaker.

If I speak, I create sound waves that vary the pressure of the air around
the ambient air pressure value. I can capture that speech with a
microphone, which turns the sound pressure signal into an analog voltage
signal (look up the definition of the word analog, as in analogy -- the
voltage in an analog of the sound, in that it carries the same
information in a different form). Now I can record that analog voltage
to disk, and I can stick it on an iPod.

Later, the iPod will play this sound by turning the numbers in the file
back into a voltage analog of the sound, then amplifying the voltage,
then handing that voltage drive to the earphones, which generate sound
pressure that varies in a way that is like the original sound that I made
that you can (hopefully) understand the speech.

--
http://www.wescottdesign.com

 

[Bob Masta]

On Wed, 30 Sep 2009 22:45:59 -0700,
unknown.hero@aa.ee wrote:

What is a "vibrating voltage"? Does that mean that, in your example, the
voltage is turning on and off or changing directions at 422 times per
second?

What exactly does it mean for voltage to "vibrate"?

Thanks for your time.

To see what a "vibrating voltage" looks like, you
can use an oscilloscope. It draws a graph on its
screen that shows the instantaneous voltage versus
time. The voltage can go positive or negative
(called AC for Alternating Current). If you
connect a microphone to the scope and whistle into
it, you will see a nice sine wave that goes
through about 1000 of these alternations per
second.

You can download my Daqarta app to use your sound
card and microphone for this. When it starts,
click the Input button to start looking at the
input. Click the thin button under Input to open
a dialog that allows you to select Mic In (in case
it defaults to Line In or something) and adjust
the input level (set it to 0... negative numbers
are lower levels.) You can magnify the view with
PgUp.

I'll be glad to answer questions. See the Contact
page on the site.

Best regards,



Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!

 

[BobW]

<unknown.hero@aa.ee> wrote in message news:ha1fm3$ksc$1@aioe.org...

BobW wrote:
Without going through all the interim steps, the basic concept is that
the
voltage coming out of the iPod (at any given volume control setting) is
an
'analog' of the original vibrations of the source of the music.

Let's say that you're listening to somebody who was whistling into a
microphone, and let's also say that the person was whistling a pitch that
was a pure and simple sound (aka a sinusoid), and let's also say that the
whistling was vibrating the air (and microphone diaphram) 422 times per
second.

The voltage coming out of your iPod will be vibrating at the same rate,
that is at 422 times per second. When this vibrating voltage is then
applied to your headphones (because they're plugged into your iPod) then
the headphone's voice coil and diaphram will be shaking back and forth
422
times per second.

If you turn down the volume control on the iPod, or add resistance
between
the iPod and headphone's wires, then the magnitude of the voltage
vibrations at your headphones will be reduced, but the rate at which the
voltage is vibrating is still 422 times per second.

The key thing to note is that the 'shape' or 'pattern' that the
vibrations
take will always be similar, or an analog, of the vibrations of the
original whistler's microphone's diaphram. The relative size of these
vibrations will vary depending on the setting of the volume control, but
the shape of the vibrations will still be similar or analagous to the
original whistle.

So, in a nutshell, the iPod does not directly control the frequency of
what is fed to your headphones. It only is changing the voltage to the
headphones in an attempt to maintain a similar looking
pattern/shape/analog between that which has been recorded and the voltage
to the headphones.

If you want a more detailed explanation of how the entire process works
(i.e. analog-to-digital conversion, digital storage, digital-to-analog
conversion) then you'll need to do a lot of reading.

Bob

What is a "vibrating voltage"? Does that mean that, in your example, the
voltage is turning on and off or changing directions at 422 times per
second?

What exactly does it mean for voltage to "vibrate"?

Thanks for your time.

If you measure the voltage coming from a new 9V battery, its voltage over
time will remain virtually steady at roughly 9V. Of course, if you measure
long enough (20 years or so) you'll see this voltage drop to almost 0V.

If you measure the pressure of the air in a room that has no fans running,
no music playing, no persons sneezing, then that air pressure will remain
virtually steady over time.

When someone makes a noise (e.g. whistling) in that room, the air pressure
will slightly increase and then descrease in a repeating pattern at a rate
exactly that of what that person's whistle are vibrating at.

If you measure the voltage at your iPod headphones while the iPod is playing
Whistle.mp3, the voltage you measure will smoothly vibrate between, let's
say, +0.31V and -0.31V peak four hundred and twenty two times per second
(assuming that the original whistler is whistling a pitch that is at 422
Hertz (vibrations per second)).

As Bob Masta recommended, you should download his wonderful Daqarta
application and set it for its oscilloscope function, hook up a microphone
to your computer, and make some noise and see the results. Try whistling,
too, because you'll see a nice steady vibration (aka oscillation) of the
resulting waveform.

Bob
--
== All google group posts are automatically deleted due to spam ==

 

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
Does it work with ubuntu?

 

[Rich Grise]

On Wed, 30 Sep 2009 21:38:22 -0700, unknown.hero wrote:

When I plug headphones into an ipod, I know that electricity of some kind
flows through the wire into the headphones, producing sound. What I don't
understand is, what exactly is done to the electricity to make an audible
signal?

I'm pretty sure the ipod controls the volume by changing the amplitude. If
you put a variable resistor between the ipod and the headphones, you can
reduce the volume. How does the ipod control the pitch of the sound? Does
it change the voltage, or the frequency (turning it rapidly on and off), or
what?

Start reading here:
http://www.google.com/search?q=basic+electronics+tutorial
and all will be revealed to you.

Well, you might want to pick up a battery, a light bulb, a magnetic
compass, a bar magnet, and some hook-up wire.

When you've done some reading, if there's something you don't understand,
feel free to ask for clarification - we were all newbies once.

Have Fun!
Rich

 

[Bob Masta]

On Thu, 01 Oct 2009 10:42:49 -0700,
unknown.hero@aa.ee wrote:

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
Does it work with ubuntu?

Windows only. But somebody told me a while back
that he had it working under Wine.

Best regards,


Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!

 

[JeffM]

unknown wrote:

When I plug headphones into an ipod,
I know that electricity of some kind flows through the wire
into the headphones, producing sound.
What I don't understand is, what exactly is done to the electricity
to make an audible signal?

To achieve the level of understanding you desire,

a student studies these topics:
http://google.com/search?q=define:direct+current
Ohm's Law and Power calculation
Thevinin's Theory and Norton's theory
....then
http://google.com/search?q=define:alternating+current

Both of those are covered in a freshman Physics class
--in case you didn't get them in 9th grade.

How does the ipod control the pitch of the sound?

The student then studies

http://google.com/search?q=define:digital+circuit
and
http://google.com/search?q=define:digital+signal+processing

 

[Jasen Betts]

On 2009-10-01, unknown.hero@aa.ee <unknown.hero@aa.ee> wrote:

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
Does it work with ubuntu?

for ubuntu use xoscope