IainL
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| posted on 18/5/13 at 08:12 PM |
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Noise Meter Apps
How accurate are noise meter apps on the iPhone?
Just thought I would check to see how loud my car was after fitting a new airbox & the "How Loud" app registered between 98-99
decibels @ 7500rpm
How confident would you be going to a track with a 100 decibel limit after that?
Cheers
Iain
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snapper
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| posted on 18/5/13 at 08:29 PM |
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Not very
The mic on an iPhone is very basic and the software not calibrated
It's a guide only
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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scottfraser
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| posted on 18/5/13 at 08:43 PM |
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Some are pretty accurate. I'm an audio professional, and use JL Audio's app that has an SPL meter, it tracks my standard SPL meters quite
well. I've also got a computer program called SMAART that I use to monitor various gigs I do, and the JL Audio is normally within a dB of what I
measure with the whole SMAART rig.
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rb968
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| posted on 18/5/13 at 08:47 PM |
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I borrowed a calibrated meter recently and compared it to my iPhone 4 app. At normal office levels it was out by about 12%.
So not very accurate unfortunately.
Rich
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coyoteboy
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| posted on 19/5/13 at 08:54 AM |
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I've seen 3 different phones running the same app say next to each other reading totally different values. Never compared them to a calibrated
meter but 2 out of the 3 would have to be out. So not very.
[Edited on 19/5/13 by coyoteboy]
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craig1410
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| posted on 19/5/13 at 10:51 AM |
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I found my iPhone sound level app (SPL Meter) was spot on but you need to ensure you use a very similar distance and angle to the exhaust pipe as will
happen in the real test. You also need to ensure that the exhaust gases are not "blowing" into the mic so you might need a muffler on the
microphone. Remember to test the car at the correct RPM as well.
Let's put it this way, it's a lot more accurate than the typical human ear so should be better than nothing. If you want greater accuracy
then you might need to use a larger, more accurate microphone which you can do. Some sound level apps even have settings to accommodate some of the
popular external mics.
C.
[Edited on 19/5/2013 by craig1410]
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Confused but excited.
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| posted on 19/5/13 at 01:20 PM |
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quote:
Originally posted by scottfraser
Some are pretty accurate. I'm an audio professional, and use JL Audio's app that has an SPL meter, it tracks my standard SPL meters quite
well. I've also got a computer program called SMAART that I use to monitor various gigs I do, and the JL Audio is normally within a dB of what I
measure with the whole SMAART rig.
As db is measured on a logrithmic scale, within 1db isn't that accurate. A difference of 3db is a difference of 10 times in noise level.
Never really thought about it with regard to track levels, but is it also A loaded when they measure it, same as when it's measured in a working
environment?
Tell them about the bent treacle edges!
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enginearin
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| posted on 19/5/13 at 01:56 PM |
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quote:
Originally posted by Confused but excited.
quote:
Originally posted by scottfraser
Some are pretty accurate. I'm an audio professional, and use JL Audio's app that has an SPL meter, it tracks my standard SPL meters quite
well. I've also got a computer program called SMAART that I use to monitor various gigs I do, and the JL Audio is normally within a dB of what I
measure with the whole SMAART rig.
As db is measured on a logrithmic scale, within 1db isn't that accurate. A difference of 3db is a difference of 10 times in noise level.
Never really thought about it with regard to track levels, but is it also A loaded when they measure it, same as when it's measured in a working
environment?
If Scott uses SMAART for a living i think he's aware of the log scale. 3dB is a doubling of sound power i.e. 96dB has double the sound power of
93dB. An arbitrary 10x multiplier has no relation to anything in dB's and what is noise level? 
I'm also surprised that multiple iphones are very different to each other as per coyoteboy's previous post. The reason that they are so
good for audio apps is that the signal path is consistent between devices, hence APP developers can guarantee the app performance. Generally i would
expect the same app on different physical iphones (of the same series 3, 4, 4s, etc.) would give consistent results for the reasons above, whether
this is ultimately the correct value is something that only testing can verify.
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Ivan
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| posted on 19/5/13 at 01:58 PM |
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quote:
Originally posted by Confused but excited.
quote:
Originally posted by scottfraser
As db is measured on a logrithmic scale, within 1db isn't that accurate. A difference of 3db is a difference of 10 times in noise level.
Never really thought about it with regard to track levels, but is it also A loaded when they measure it, same as when it's measured in a working
environment?
I thought that a 3db difference was roughly twice or half the noise level depending on which way you are looking at it.
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MikeRJ
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| posted on 19/5/13 at 02:11 PM |
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quote:
Originally posted by Ivan
quote:
Originally posted by Confused but excited.
quote:
Originally posted by scottfraser
As db is measured on a logrithmic scale, within 1db isn't that accurate. A difference of 3db is a difference of 10 times in noise level.
Never really thought about it with regard to track levels, but is it also A loaded when they measure it, same as when it's measured in a working
environment?
I thought that a 3db difference was roughly twice or half the noise level depending on which way you are looking at it.
3dB gives you a doubling (or halving) of sound power.
6dB gives you a doubling (or halving) of sound pressure level.
However, since the human ear has a logarithmic response to SPL, it actually takes an SPL change of approximately 10dB for a perceived doubling (or
halving) of volume level.
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MikeRJ
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| posted on 19/5/13 at 02:15 PM |
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quote:
Originally posted by enginearin
The reason that they are so good for audio apps is that the signal path is consistent between devices, hence APP developers can guarantee the app
performance.
I very much doubt the iPhone was ever designed to have a particularly close tolerance on the gain of the signal path. It would mean high precision
resistors and capacitors would be required, coupled with a calibrated microphone which would add a lot of unnecessary expense.
[Edited on 19/5/13 by MikeRJ]
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craig1410
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| posted on 19/5/13 at 04:02 PM |
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Some useful info here on iPhone Mic performance from the company who produce SPL Meter (the one I use):
http://www.studiosixdigital.com/iphone_hardware/iphone_3gs_microphone.html
Note what they say about iOS versions prior to iOS 6 having a low pass filter which can now be switched off by the application for iOS6 upwards. This
is probably quite important for measuring sound level of a car engine which will have some low frequency sounds for sure. If you have access to a
calibrated SPL meter then you can also calibrate this app.
Also some good info on an external fully digital interface Mic here:
http://www.studiosixdigital.com/itestmic/itestmic.html
"When you plug iTestMic into any iOS device running AudioTools, the factory calibration values are read and applied, giving you an instantly
available accurate SPL measurement tool calibrated to +/-0.1 dB, no matter what iOS device you are using." - Sounds like a bold but confident
claim. If you read some of the stuff on this website it certainly sounds like these guys know what they are doing and the app is aimed at audio
professionals and has good reviews so maybe it works pretty well.
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