

How Accurate Are These Smartphone Sound Measurement Apps? - liyanage
http://blogs.cdc.gov/niosh-science-blog/2014/04/09/sound-apps/

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SwellJoe
That's better than I would have thought, and in some cases on par with very
low cost (sub-$50) dedicated SPL meters.

I have a side business that does audiovisual services, and I've been meaning
to get the other folks in the crew to test their phone with one of these apps
against my SPL meter (which is a ~$80 unit that I believe is pretty accurate
in most circumstances), so they'd have a ballpark idea of how loud they're
running the gear (there are noise ordinances that we sometimes have to take
responsibility for following).

I'd be curious how well a phone could act as an RTA, as well. I used to use my
Amiga to do analysis (non-realtime, but reasonably useful in a time when
having a high resolution spectrum analyzer was amazing), and standard PCs have
been able to act as RTAs for at least 15 years, so I'm absolutely certain the
processing power needed is there in modern phones and tablets, but the mic and
audio interface would be a limiting factor.

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thisjepisje
Maybe you could get an idea of the accuracy by e.g. feeding white noise to the
phone and seeing how flat the spectrum is? And though I've never used them
personally, I hear there are some pretty good clip-on microphones for
smartphones on the market.

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baldfat
AS a former Sound Engineer and Studio owner I am blown away at what a phone
can do now a days. It really is asy to have someone down load an app and talk
them through live sound and EQ with the visual (accurate or not) to show what
happens with sound when they play with cheap EQ (AKA cheap EQ is always for
REDUCTION and never amplification)

I think if I was doing any sound work anymore I would quickly pick up an
external mic and just always use pink noise and the meter to rough in a
system.

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BuildTheRobots
out of curiosity, what app(s) do you have them download?

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baldfat
I don't have an answer, sorry.

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jwr
I've been using SPLnFFT for a while now, with consistent results and I'm happy
to see a formal evaluation.

The problem that remains is that there are differences in microphones between
iOS devices. SPLnFFT author should probably calibrate the app on every device
that is out there on the market. I'm not sure if that's at all feasible.

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jimsandy67
They're now running a similar study with external mics (MicW i436)

[https://twitter.com/NIOSHNoise/status/522456711882629120](https://twitter.com/NIOSHNoise/status/522456711882629120)

I expect apps would be even more accurate with external mics

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Anechoic
It's not surprising that a device around a mobile device can produce decent
results. The Bruel and Kjaer 2250 [0] and 2270 sound meters (probably
considered to be the highest-end sound meter on the market) is built around
Windows CE.

That said, the JASA paper give this very huge caveat near the end:
_Furthermore, this study examined these apps in a controlled noise
environment. Field measurement results may vary greatly due to the effect of
temperature, humidity, long-term use, object interference, and overall
stability of the microphone and electronics in these devices._

Furthermore, they tested the devices with relatively high SPL signals (65 to
95 dB), the only tested overall noise levels (no frequency response testing)
and in a reverberant field so these results may not be applicable to many
other situations (temperature extremes, lower sound levels, etc)

The week point of using a smartphone as a sound meter is going to be the
microphone. If you can pair the smartphone with a precision microphone (using
something like Studio Six Digitals iAudiointerface [1] for example) you can
have the equivalent of a IEC Class 1/ANSI Type 1 microphone (I and colleagues
have used this setup for sound measurement projects involving litigation). But
if you're depending on the device's internal microphone, be very careful at
how you apply those results, especially given the vacates listed in the paper.

That said a smartphone sound meter apps will get you in the right ball park,
and as alluded to by SwellJoe they can be at least as accurate (if not more
accurate) than some of the $50-$100 Type 2 meters on the market. Just don't
rush to any conclusions based solely on data obtained from those setups.

[0] [http://www.bksv.com/Products/handheld-instruments/sound-
leve...](http://www.bksv.com/Products/handheld-instruments/sound-level-
meters/sound-level-meters/type-2250.aspx)

[1] [http://www.studiosixdigital.com/audio-
hardware/iaudiointerfa...](http://www.studiosixdigital.com/audio-
hardware/iaudiointerface2/)

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ADent
From a comment at the link:

"NIOSH does not recommend nor endorse a particular commercial product. The
data from our study “Evaluation of smartphone sound measurement applications”
is available in the journal article referenced at
[http://scitation.aip.org/content/asa/journal/jasa/135/4/10.1...](http://scitation.aip.org/content/asa/journal/jasa/135/4/10.1121/1.4865269)
. The discussion section (page 189) highlights two apps — SoundMeter and
SPLnFFT — that had the best accuracy over our testing range. There were two
other apps — Noise Hunter and NoiSee — that were within ± 2dB of the reference
sound source. Once again, note that the data results in the study do not
constitute as NIOSH endorsement of any of these products."

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vdnkh
I'd like to have seen a few tests with Windows Phone (somebody must care about
us!). My Lumia Icon has 4 "high def" microphones with great claims of accuracy
and background noise reduction from Nokia. In my experience they've worked
well but I don't have an SPL to compare it against.

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72deluxe
Pity it only mentions iOS apps and not the ones I use on Android. I use two
apps and they read radically different values (unless I am reading them wrong
- that might be the case).

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ISL
Read their paper (
[http://scitation.aip.org/content/asa/journal/jasa/135/4/10.1...](http://scitation.aip.org/content/asa/journal/jasa/135/4/10.1121/1.4865269)
) , it's free to read the PDF.

The hardware is at least as important as the software (I'm amazed to see so
much scatter between apps), so the homogeneity of the iOS ecosystem is a boon
to this sort of measurement. Figure three in their paper shows that the Apple
hardware is quite consistent across all models tested.

They did test Android phones and apps; the final paragraph from their results
section makes a general statement:

 _A similar examination of Android apps and devices was not performed because
of the low number of apps with similar functionality, and the lack of
conformity of fea- tures between devices. Testing conducted with the four
Android smartphones also revealed a high variance in measurements of similar
apps between different devices._

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72deluxe
Apologies - I did go and take a look at the paper but examined the graphs and
scanned the last paragraph but saw iOS everywhere; a more concentrated reading
would have stopped me making a fool of myself.

Thanks for pointing the paragraphs out.

