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View Full Version : App to find average db? - soundbooth?




LERsince1991
Mar 21, 2010, 06:57 AM
Hi, im looking to do some analysis work on a location and want to take readings to see how loud it is in various places today.

So I'm trying to record or take readings using an app, not sure what to use but I've looked at soundbooth, and I can record stuff but not sure how to find out the average db amplitude for each recording? anyone help?

Cheers,
luke.

edit: I believe I'm looking to find the RMS values of a recording?



ChrisA
Mar 21, 2010, 11:18 AM
Hi, im looking to do some analysis work on a location and want to take readings to see how loud it is in various places today.


You mean you want to take an absolute measurement? Not a relative one.

Software (any software) can only tell you the fraction of full scale. For examlle it can tell you the files is recorded at "-3db" but that tells you noting about how loud the actualy sound was.

For that you need a calibrated meter like this
http://www.radioshack.com/product/index.jsp?productId=2103667

OK, you can calibrate you mic, preamp and recording setup but you'd need a meter to preform the calibration.
Surprizingly these "rat shack" meters have become a kind of standard

Luap
Mar 21, 2010, 11:26 AM
For loudness readings within an existing recording, I use AudioLeak.
http://www.apple.com/downloads/macosx/audio/audioleak.html

LERsince1991
Mar 21, 2010, 12:47 PM
Thanks for the replies!

ok well I don't fancy buying anything, the measurements don't need to be very accurate but they do need to be relative. I want to compare the loudness between 10 locations for an analysis.

I've just done it, not sure how good it is but its alright for now. Basically I took my laptop, recorded 2 minutes in each location and used soundbooth to analyse the recordings to show the average volume, the average perceived volume and the peak volume. then made a graph from these, I can also see what the main frequencies in each area are.

However! - I will be doing this again soon as I want better data for my final submission so any more comments would be very helpful!

I would like to know would using a better microphone (the ones with the furry covers on) so that wind doesn't void my results. I ask this because today in my current recordings the wind seemed to 'spike' my macbook's mic and create peaks in my samples.

Thanks again everyone!
Luke.

ChrisA
Mar 22, 2010, 12:29 PM
T..the measurements don't need to be very accurate but they do need to be relative.

I would like to know would using a better microphone (the ones with the furry covers on) ..

Yes, "relative" is easy to do, as you found out.

One thing to watch out for is the frequency response of the microphone. Your relative loudness is being measured only within the freq. limits of the mic. For example your Macbook's built in mic might be ignoring a loud kick drum or more likely under-measuring it.

There are industry standard frequency response curves used for measuring sound volume. If you want to publish your work and have have others understand it you need to worry about this.

You could use a basic mic like the Shure SM58 with a wind screen. But as much as I hate to recommend that "B" brand name they do make a nice inexpensive Mic just for your purpose. Some people make these DIY. You can buy the parts for cheap and mount them inside a length of PVC pipe. There are some on-line writeups about this. But for $49 it is hardy worth the effort. Put this or any mic inside a wind screen and you are good to go.



http://www.zzounds.com/item--BEHECM8000

Lots of windscreens here
http://www.sweetwater.com/c379--Windscreens/low2high/all

LERsince1991
Mar 22, 2010, 01:57 PM
Very informative reply thank you !

So just to make sure,
If I can get a good mic from the media department at my uni to borrow with a wind screen I can pretty much do as I have done, record to my macbook and analyse in soundbooth?

Its pretty hard to get good readings with a laptop in my hand, would anyone happen to have any good ideas of other ways to record without loosing quality?

hakukani
Mar 22, 2010, 07:09 PM
I'd go with the SPL meter from radio shack above. It has an internal mic, and gives fairly accurate readings. It's certainly less than a textbook.

Maybe someone at your uni has an SPL meter??