16
\$\begingroup\$

I have a project in which I am considering using the microphone from a smartphone for the reception of inaudible signals (> 15khz).

What is the frequency range that such a microphone of receive sound? And what is the maximum frequency ?

\$\endgroup\$
  • \$\begingroup\$ Brand and model of cell phone please! \$\endgroup\$ – placeholder Feb 26 '13 at 2:35
  • 1
    \$\begingroup\$ In actuality for most modern phones, you are likely to see the lowpass filter in the ADC and related signal chain, often at around .45 FS rather than the microphone. \$\endgroup\$ – Chris Stratton Feb 26 '13 at 13:11
  • 5
    \$\begingroup\$ 15kHz isn't inaudible. \$\endgroup\$ – Marquis of Lorne Nov 1 '14 at 22:05
  • \$\begingroup\$ I would be quite impressed if a smartphone microphone did even 10kHz or 12kHz. \$\endgroup\$ – DKNguyen Oct 9 '19 at 18:54
24
\$\begingroup\$

The best idea is to ignore what everyone says, and test it yourself. Install an app like "SpectralPro Analyzer", and either generate some high frequency sounds using PC programming (easy) or download some high-frequency MP3's from web sites.

I've done all of the above on many different phones - I find that I get excellent results for a very long way off the top of my hearing range, at least as high as 21kHz (the limit for those apps). The interesting thing about this is:
a) everyone who said PC speakers can't do 21kHz was wrong, and
b) everyone who said smartphone microphones can't pick up high frequencies was wrong too.

Bottom line - almost everyone who's never tried this stuff makes a guess. Good intentions don't make their guessing relevant though :-(

Best of luck with your project!

Here's a Samsung Galaxy Note-1 recording a Macbook Pro signal which went from 9kHz to 21kHz:

spectograph recording

(Image source)

| improve this answer | |
\$\endgroup\$
  • 3
    \$\begingroup\$ it's not a binary statement though. That is the microphone may catch high frequency but with more attenuation than other frequencies. The mic has a resonance frequency where it has the maximum sensitivity and also there are circuits that deliberately attenuate inaudible frequencies. Anyway many modern MEMS mics have a flattened response curve (gain as a function of applied frequency) so the test suggested here is the only way to be 100% sure. \$\endgroup\$ – fhlb Jul 14 '16 at 17:11
4
\$\begingroup\$

This is likely to be different for each manufacturer / model and something you'll either need to test yourself or do some searching of manufacturer specifications and/or tests that other have performed. For example here's an iPhone microphone frequency response comparison:

http://blog.faberacoustical.com/2009/ios/iphone/iphone-microphone-frequency-response-comparison/

Also note that many people, especially the young, can hear up to 20 kHz and sometimes beyond so what you're trying to achieve probably won't be possible on most phones.

| improve this answer | |
\$\endgroup\$
4
\$\begingroup\$

Apparently it is possible for a smartphone microphone to pick up on sounds that most people can't hear, because:

"Narrate's Zoosh software leverages smartphones' speakers and microphones to enable the same data communications between devices that today's NFC provides, but with ultrasonics frequencies that are inaudible to humans." -- Eweek, Slashdot.

| improve this answer | |
\$\endgroup\$
3
\$\begingroup\$

It depends entirely on the phone, they will all use different microphones/circuits.
Generally, an audio mic will be within a range of 20Hz - 20kHz. Many cheaper mics ( or intended for voice only) will have a lower cutoff frequency of 15kHz or less. The circuit the mic is attached to may intentionally roll off the frequency - various DSP techniques are used to minimise background noise and feedback, adjust compression, etc - so the software processing is quite sophisticated and dynamic on a modern mobile phone.

At a guess, you should be able to rely on at least 100Hz - 10kHz.

For a particular model, have a look at the specs, it should give at least some basic detail on the microphone input range. Or do some testing with a function generator and some recording app on the phone.

| improve this answer | |
\$\endgroup\$
1
\$\begingroup\$

As a first time iPhone user (and trained BBC recordist) I am beyond impressed by the audio. Spectrum analyser app (Octave RTA) registers down to 16 Hz and up to 20 kHz on my iPhone 7. Live concert organ is very well recorded, pedals and all, albeit mono. The 19kHz pilot tone leakage from an FM radio speaker is perfectly visible.
I have no way to confirm flatness of response, though a natural white noise source such as a waterfall is displayed without evident peaks or banding. Recording speeach alongside a good studio condenser mic there's really not a lot of difference, just a bit bass light and mid-treble bright, easily EQ'd. Hope Apple never change the mic or input. Or maybe they did later?

| improve this answer | |
\$\endgroup\$
1
\$\begingroup\$

The best way to tell would be to locate which MEMS mic is in your phone and finding the data sheet.

Testing it yourself without lab quality equipment will have many problems, including:

1) other posts have recommended just playing a frequency sweep on your speakers. The issue here is your speakers (with enclosures) themselves have a frequency response that is not flat, so you're introducing a frequency sweep that is already transformed by the frequency response of the speaker dynamical system.

2) You do not have a reference lab quality microphone with flat frequency response to compensate for 1.

3) The fact that the microphone is enclosed in your cell phone case will change the frequency response due to the effect of the microphone inlet geometry, see articles on Helmholtz resonance and audio design.

Outside of a lab environment, it will be really difficult to get a meaningful frequency response.

| improve this answer | |
\$\endgroup\$
0
\$\begingroup\$

Just a note: The maximum frequency you can get from your microphone is half the sampling speed of the AD converter. So half the sampling frequency.(nyquist freq?) (you need two samples to make a minimal "wave")

I've read that an electret microphone (if that is what is used) should be able to detect frequencies in up to 30kHz. If you would want to detect this signal you'd have to sample at 60kHz , i have no idea if you can change your microphone input sample freq, on smartphones .

| improve this answer | |
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.