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Mobile phone SPL meter: 110 dB range?

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schmitt trigger

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Please look at the attached image: it is a screenshot of sound level meter available for the IPhone 8.

My question is, look at the range, from 20dBC to 130 dBC. Really?
How can they get 110 dB dynamic range, from a mobile phone?

PD; I would not want to be exposed to a 130dBC SPL without some sort of ear protection.
 

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JimB

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JonSea

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Better break out the hearing protection way below 130 dB!

I would suspect that different gain settings are used to cover the 110 dB range.
 

schmitt trigger

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I believe that the beach is now closed after some tourists had some serious injuries.

Anyway, I have seen professional SPL meters with gain range change, but this seems to have a continuous range.

Doing the calculations, this would mean an ADC in excess of 18 bits. My skepticism is whether that was implemented on a phone.
 

JonSea

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The display shows a single number. That doesn't mean that a single range is used to get that number. Say each range has a dynamic range of 60 dB.

Start with maximum sensitivity.

Read value.
Is value maxed out?
YES - decrease sensitivity and measure again
NO - display value

It's not showing a spectrum where you can see a noise floor at 30 dB and peaks at 110 dB. Displaying a single value provides no clue what the dynamic range of the measurement is.
 

ronsimpson

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Doing the calculations, this would mean an ADC in excess of 18 bits. My skepticism is whether that was implemented on a phone.
I have worked on a phone project once.
A low end audio ADC is 16 bit. If it was a separate IC in the phone.
It most likely is in side a large IC so the noise level might be 18 bits on a 16 bit ADC. (or worse because who cares)
I am certain there is Automatic Gain Control.
With hardware AGC a very bad ADC could have a very large range. Add 40db of variable gain in the input of the ADC .....
It could have a good ADC and the AGC is in software. Who knows.

I have some very old audio ADCs here in recorders. 16 bit is the smallest I have.
 

tomizett

Active Member
Regardless of how the the preamp and ADC are implemented, it still implies that the microphone will handle 130dB SPL linearly... which seems pretty unlikely!
 

ronsimpson

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seems pretty unlikely!
A quick look at Digikey.com (small microphones) Some show noise level and clipping level. The ones I found have 91 to 96 db range. Phones likely don't have full bandwidth which will help a little. So I agree.
 

schmitt trigger

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That is exactly my question......I would be difficult to find a transducer with such a wide dynamic range. Probably on a professional instrument, not on a mobile phone.
 

audioguru

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A cheap electret mic can have a much wider sound level range, especially much more range for louder sounds when it has the 3-wires Linkwitz modification where the common-source 2-wires Jfet inside it is converted to a 3-wires common-drain follower as is shown in this video:

 

tomizett

Active Member
That's interesting AG... thanks for posting.
The audio quality of modern phones (especially with respect to noise canceling etc) it truly impressive - don't get me wrong. It's just hard to believe that a device optimised for voice quality would give this dynamic range (especially 130dB at the top end).
Seems more likely that the progammer just read an 18-bit number and scaled it into dB's without too much considderation of how legitimate the result would be.
A bit like reading 010V on your 1% accurate multimeter and interpreting it as 10.000000V.

Real sound level meters are, of course, calibrated - there's no real way of doing that on a mobile phone. That said, I know audio professionals who use such apps (especially spectrum analysers) as very useful tools.
 

ronsimpson

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I have two sound level meters.
The analog one has a switch that sets the middle of the meter to read at: 120db, 110, 100, 90, 80, 70, 60db
The analog meter range is -6db through +6db.
I think the range is +126db to 54db
AND
I have a digital sound level meter.
The range is 130db to 40db.

OK these are not high end meters, but they are OK.
 
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