A chicken-and-egg question about microphones (and clocks)

Jim Nazium · #1 10-17-2010, 02:38 PM

To measure the frequency response of a speaker, you need a calibrated microphone, right? You need to know the frequency response of the microphone. How do you determine that? By testing it against a calibrated speaker? But that speaker was tested with another mike which was tested with another speaker which ...

How does it all start?

Similarly, how do we know what is the world's most accurate clock? What do you test it with? If you test it with some physical phenomenon, assumed to occur at a constant frequency, then isn't that the most accurate clock?

This stuff keeps me awake at night. Your help is appreciated. kthxbai

NateS · #2 10-17-2010, 04:52 PM

Quote:

Originally Posted by Jim Nazium

To measure the frequency response of a speaker, you need a calibrated microphone, right? You need to know the frequency response of the microphone. How do you determine that? By testing it against a calibrated speaker? But that speaker was tested with another mike which was tested with another speaker which ...

How does it all start?

Similarly, how do we know what is the world's most accurate clock? What do you test it with? If you test it with some physical phenomenon, assumed to occur at a constant frequency, then isn't that the most accurate clock?

This stuff keeps me awake at night. Your help is appreciated. kthxbai

as far as clocks go, a second is:

"Since 1967, the second has been defined to be
the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom"

thusly, they picked one clock and said "that's right".

for the speaker/microphone...i dunno.

Thunderscreech · #3 10-17-2010, 05:08 PM

How do we know what colors are? Does the way I see Red differ from how someone else sees it?

flowlikeocean · #4 10-17-2010, 05:17 PM

Quote:

Originally Posted by Thunderscreech

How do we know what colors are? Does the way I see Red differ from how someone else sees it?

This sounds kind of like it belongs in the, "Cannabis" thread.

NateS · #5 10-17-2010, 05:33 PM

Quote:

Originally Posted by Thunderscreech

How do we know what colors are? Does the way I see Red differ from how someone else sees it?

i have a long and very in-dept theory about this. don't feel like typing it.

jp58 · #6 10-17-2010, 05:47 PM

Quote:

Originally Posted by flowlikeocean

This sounds kind of like it belongs in the, "Cannabis" thread.

Now children, dugs, drugs are bad.... mmmkay?

Skitch it! · #7 10-17-2010, 06:05 PM

I only read the OP and I'm a trippin', stop thinking so hard on yourself : )

fdeck · #8 10-17-2010, 06:08 PM

Quote:

Originally Posted by Jim Nazium

To measure the frequency response of a speaker, you need a calibrated microphone, right? You need to know the frequency response of the microphone. How do you determine that? By testing it against a calibrated speaker? But that speaker was tested with another mike which was tested with another speaker which

The basic process is with a microphone that can also operate as a speaker. You can then use a number of these devices to calibrate one another:

http://en.wikipedia.org/wiki/Measure...ne_calibration

Quote:

Similarly, how do we know what is the world's most accurate clock? What do you test it with? If you test it with some physical phenomenon, assumed to occur at a constant frequency, then isn't that the most accurate clock?

Likewise with clocks, you have to build a bunch of them, operate them under different conditions, and see if they keep time with one another. Nowadays, it's also possible to test one type of atomic clock against another type. These guys have a few different models to choose from:

http://www.symmetricom.com/products/...tandard/5071A/

SMILEYSIXX · #9 10-17-2010, 06:17 PM

My brain has been successfully liquified and is currently pouring out of my ears. If I took shrooms, this all might start making sense.

SMILEYSIXX · #10 10-17-2010, 06:19 PM

I feel the urge to throw a curveball. So here's a little DesCartes.

What is real?

On your mark... get set... GO!

tplyons · #11 10-17-2010, 07:16 PM

Quote:

Originally Posted by Thunderscreech

How do we know what colors are? Does the way I see Red differ from how someone else sees it?

I wonder this all the time...

Skitch it! · #12 10-17-2010, 07:18 PM

Quote:

Originally Posted by tplyons

I wonder this all the time...

Depends on which 'Red' your drinking ; )

iamlowsound · #13 10-17-2010, 07:47 PM

As far as clocks go, I am not sure how they determined what one is correct -- the answer above seems good -- but the American atomic clock is the clock that most watch makers set their timing to. Or at least that is what my uncle says and he is a watch maker.

lowsound

fdeck · #14 10-17-2010, 07:52 PM

Quote:

Originally Posted by Thunderscreech

How do we know what colors are? Does the way I see Red differ from how someone else sees it?

It seems a safe bet to me that any explanation of color vision starts with knowing that there are four types of light receptor cells in the retina, and also probably has to do with evolved survival traits such as the ability to spot good food.

fdeck · #15 10-17-2010, 08:03 PM

Quote:

Originally Posted by iamlowsound

As far as clocks go, I am not sure how they determined what one is correct -- the answer above seems good -- but the American atomic clock is the clock that most watch makers set their timing to. Or at least that is what my uncle says and he is a watch maker.

lowsound

As I understand it, there is an international time standard that is agreed upon by treaty and maintained by a large number of clocks scattered all around the world. National time standards are based on international time. You can get the national time standard in a number of ways, for instance WWVB is a radio station whose broadcast frequency is synchronized to an atomic clock. There are also ways to get accurate time from the cell phone system, GPS, and the Internet. Each of these systems has its own pro's and con's of course, ranging from cost to absolute accuracy.

Thunderscreech · #16 10-17-2010, 08:05 PM

Quote:

Originally Posted by fdeck

It seems a safe bet to me that any explanation of color vision starts with knowing that there are four types of light receptor cells in the retina, and also probably has to do with evolved survival traits such as the ability to spot good food.

Yes, but is what I call "red" something else to someone else, like, say "dark orange" or "red orange"? I mean, the difference is in what we see vs. what we call what we see.

Or at least I think it is. I dunno, I quit knowing what I was talking about two sentences ago. What?

fdeck · #17 10-17-2010, 08:12 PM

Quote:

Originally Posted by Thunderscreech

Yes, but is what I call "red" something else to someone else, like, say "dark orange" or "red orange"? I mean, the difference is in what we see vs. what we call what we see.

That seems pretty likely. I suspect that we use whatever terminology makes sense for what we are talking about. We can say that a red light at a traffic intersection is red, with no ambiguity. Picking out different shades of red at a paint store might require more verbose description. And the machine at the paint store that can duplicate a paint color "sees" it as just a bunch of numbers.

DerHoggz · #18 10-17-2010, 08:19 PM

Quote:

Originally Posted by fdeck

That seems pretty likely. I suspect that we use whatever terminology makes sense for what we are talking about. We can say that a red light at a traffic intersection is red, with no ambiguity. Picking out different shades of red at a paint store might require more verbose description. And the machine at the paint store that can duplicate a paint color "sees" it as just a bunch of numbers.

I think Thunderscreech meant more along the lines of we call that color red, and so do other people, but are they seeing the same color that I am. I am a little red green colorblind, and my mom has a blue coat that everyone says is purple, I can't see the red in that specific instance.

coreyfyfe · #19 10-17-2010, 08:29 PM

Quote:

Originally Posted by Thunderscreech

How do we know what colors are? Does the way I see Red differ from how someone else sees it?

Ever put pressure on one of your eyes (like sleeping on top of your arm or something) then open both eyes and notice that one is slightly blue-shifted in relation to the other? Or one is red-shifted in relation to the other? I always feel like I'm wearing old-school 3D glasses when that happens.

On topic, colors correspond to specific wavelengths of light, so really, how you interpret it is irrelevant. We all just have to learn how to measure light and start referring to colors by their specific emission spectra.

fdeck · #20 10-17-2010, 08:31 PM

Quote:

Originally Posted by DerHoggz

I think Thunderscreech meant more along the lines of we call that color red, and so do other people, but are they seeing the same color that I am. I am a little red green colorblind, and my mom has a blue coat that everyone says is purple, I can't see the red in that specific instance.

Amusingly, I have a friend who managed a project to develop one of the first color matching systems for paint stores, and he's colorblind. Also, I work with another friend in a laser lab, and while he is not considered to be colorblind, there are longer wavelengths (780 nanometers) that I can see, but he can't.

I think the same "stuff" is coming into our eyeballs. But there are certainly genetic variations in how we sense that stuff, e.g., forms of colorblindness, and probably in how our brains categorize and process the information.