MNorman


Just to complete this, 20 micropascals = .0002 micro bars = about 2.9 billionths of a psi

A programming language used to describe tiny a pie bar?

Karyn, go pick up a cheap SPL meter for around $30. Your daughter will have fun going around measuring sound levels and afterward you can use it to calibrate your studio monitors.

This one's pretty good, if a little pricey:

http://www.radioshack.com/product/index.jsp?productId=2103667

MNorman


This one's pretty good, if a little pricey:

http://www.radioshack.com/product/index.jsp?productId=2103667

I have that one.

Yeah, me too.  Gets the job done.  And it has a hold for a tripod.

Karyn


I should have said that the advantage of decibels is that you can simply add/subtract them to convert between different scales.

So taking a few examples from Wikipedia

Vuvuzela  +120
Jack hammer +100
Passenger car @ 10m  +70
Washing machine +50
Whispering  +25
Leaves rustling +10

Now record your own Vuvuzela (you do have one don't you?) and set gain to read Full Scale.  0bDFS
The other items would show as
Jack Hammer -20
Passenger car @ 10m  -50
Washing machine -70
Whispering  -95
Leaves rustling -110

This really puts it into perspective and helps alot.  Thanks.
 
<< dBFS = how much quieter a sound is compaired to a sound that would make your equipment read full scale. >>
 
Does this mean "Jack Hammer -20dB" in the example above could be different perceived volume if recorded on or played back on different equipment?  Does this scale (dBFS) only refer to recorded sound? (ie. "... your equipment")
 
 

SH

 
<< dBFS = how much quieter a sound is compaired to a sound that would make your equipment read full scale. >>
 
Does this mean "Jack Hammer -20dB" in the example above could be different perceived volume if recorded on or played back on different equipment?  Does this scale (dBFS) only refer to recorded sound? (ie. "... your equipment")
 
 

The perceived volume on playback would depend on the size of amplifier you play it through...   The recording level will be determind by the gain of your input amp.  This is where calibration is important.
 
If you buy an expensive (or cheap) sound level meter then you're paying for the calibration of its mic amp to be accurate.
 
 
dBFS (Full Scale) is simply a level that makes your meters hit Full Scale.  It is a good choice to use because it is very easy to calibrate. You simply choose the loudest sound you want to record and adjust the input gain untill the meters read Full Scale.

If you have two or three or more recorders, perform the same calibration on them with the same sound source at the same distance and all your equipment will give you the same readings.
 
Use a table of known levels from Wiki to convert your dBFS readings to dBspl if you wish as I showed you before.

What is the source of the sound? If you're trying use a meter to calibrate  or compare you need a steady state sine wave. 1 Khz sine is a typical reference for normal hearing.

Just when I think there's nothing to learn in the Coffeehouse.... :D

Rbh


What is the source of the sound? If you're trying use a meter to calibrate  or compare you need a steady state sine wave. 1 Khz sine is a typical reference for normal hearing.

Read the OP,  "My daughter is using Sonar for a science experiment to measure the relative volume of different sounds."
 
All she needs do is set the input gain so that the loudest sound she's testing reads Full Scale (0dBFS) then all the other sounds will be x y z dB quieter than that.   As long as the input gain is not changed (I sujested gaffer tape on the knob) then there is no further calibration to do.
 
 
Example:
 
She records the household washing machine from 1m distance. Sonar shows a level of -60dBFS.   She goes to Wikipedia and finds the SPL for the average washing machine is around +50dBspl  so she has a reference.
 
Now she records a guitar amp with her kid sister/brother/family pet bashing away on the strings.  Sonar gives a level of -30dBFS.
Straight away she has fullfilled the aim of the school project.  The guitar is 30dB louder than the washing machine. 
 
Further, she can take her reference sound from Wiki (Washing machine +50dBspl) add 30dB and say the guitar was playing at +80dBspl.
 
As long as the input gain is not touched that will work all day long with no further calibration.