With the advent of sound level meter apps for the iPhone OS (of which SoundMeter was the first) people began to ask, “How flat is the frequency response of the iPhone’s microphone?” Early testing indicated that the built-in microphone of the original iPhone was not a good candidate for sound level measurements, but that the iPhone’s headset microphone enjoyed a fairly flat response. Since then, additional iPhone models have arrived on the scene, each with its own set of weaknesses with respect to microphone frequency response. Additional Apple and third party headset microphones have also been introduced.
At long last, some relevant frequency response measurements are presented here for the benefit of those who would really like to “see” how flat a particular microphone is. These results have implications on the use of certain microphones for making sound level measurements, as well as on the use of these microphones for spectral analysis in which relative amplitudes need to be determined with some degree of accuracy.
The following measurements were made relative to a Type 1 precision microphone in a fairly quiet room. These measurements were not made in an anechoic chamber and although the coherence was very good across the audio band, the measurement error is non-negligible at high frequencies, because of diffraction effects.
Built-in Microphones
Built-in iPhone Microphone Frequency Response Comparison
As I have often said, “The built-in microphone of the original iPhone is not recommended for sound level measurements.” Now, you can really see what I mean. Interestingly, the built-in microphone of the iPhone 3GS isn’t recommended, either, unless you don’t care about frequency content below 200 Hz. This behavior is consistent with the headset input frequency response of the iPhone 3GS (I suspect that the built-in microphone signal goes through the same high-pass filter that gets applied to the headset input). The iPhone 3G microphone’s response is clearly the best of the bunch, but its low end rolls off by 15 dB or more at 20 Hz. Not surprisingly, none of the iPhone models rivals a lab-grade sound level meter with its built-in microphone, but either of the 3G models can potentially give you a decent ball-park estimate of the current sound level, although the low frequencies will be de-emphasized.
Headset Microphones
The goal, here was not to measure every headset microphone on the market, but to take a look at some of the more common options. These measurements were made of each microphone’s electrical output, so they do not include the response of any iPhone input or output circuitry. The microphones included in these measurements are:
- SwitchEasy ThumbTacks microphone
- USBFever Mini Microphone
- iPhone Headset Microphone (included with each iPhone)
- Apple Earphones with Remote and Mic
- Apple In-ear Headphones with Remote and Mic
iPhone Headset Microphone Frequency Response Comparison
In the world of headset microphones (at least those that are presented, here), the official iPhone headset microphone and the SwitchEasy ThumbTacks microphone win the day. The USBFever microphone also exhibits a flat response between 20 Hz and 2 kHz, although its response appears to break up more severely by the time it gets up to 10 kHz. In light of recent headset input frequency response measurements, the best case scenario for inexpensive sound level measurement might be to use the ThumbTacks microphone with the original iPhone.
These results are also interesting, in that they strongly suggest that the newer Apple headsets, which are designed primarily for iPods, shouldn’t be used for sound level measurements, either. Their response certainly seems to follow an apparent trend with Apple’s microphone-related circuitry to de-emphasize low frequencies.
It may be important to keep in mind that the goal, here, is to see what makes sense in terms of using iPhone OS devices as inexpensive, portable sound level and spectrum analysis tools. Obviously, there was never an expectation that the iPhone’s inexpensive microphones would perform in a manner consistent with precision measurement mics that are (justafiably) much more expensive. It is possible to connect such high-end microphones to an iPhone, though (via the dock connector)–more on that, later…
Hi,
An interesting article!
I notice on the graphs, they all appear to hit a wall at 20kHz – is this where the app stops measuring, or does the iPhone cut off frequencies above 20kHz ?
Thanks,
Darren
Darren,
The sample rate was set to 48 kHz, so the displays go up to 24 kHz. To be effective, the anti-aliasing filters of the iPhone’s analog input circuitry need to filter out frequencies above 24 kHz. What you see is the effect of the anti-aliasing filters that begin to roll off the high frequencies somewhere between 20 kHz and 24 kHz.
Ben
Do you know if the hi-pass filter on the 3GS is also active for video recording? Seems to me it would be pretty poor if it were. I hate it when they take stuff way, I’m not looking forward so much to trading up my 3G now. Why did they have to take my bass away?!
Hi-pass on the 3GS is for “wind noise”? – yeh, right – well, maybe, but I suspect it’s more intended to cripple the iPhone for live music recording. This is a really annoying move by Apple. That rolloff is so steep that it’s hard to imagine even being able to recover the bass after transferring it to a computer.
So the only way to get full-bandwidth audio into the iPhone for recording is via the dock connector and that in turn means buying an audio adapter. These are extremely hard to find and extremely expensive when you do find them. I suppose Apple is trying to reinforce those guys’ value props by crippling the main mic and forcing people to get the expensive (and VERY bulky) adapter.
Does anyone know if apps can turn off, or compensate, the bass rolloff. (I strongly suppose not but I thought I’d ask).
Does anyone know the cheapest way to get audio into the dock’s line-in connector?
Has anyone figured out a chip way to get the input through the dock connector? Does this require an authentication chip (or a particular setting on the accessory pin 21 will do the trick)?
Sign up for the Made for iPod program: http://developer.apple.com/ipod
I would be interested to see the same comparison for the speaker. Do you have this or could you generate this?
i don’t have a comparison of various iphones, however i have measured the iphone 3G speaker using CLIO. the 3G speaker rolls off at about 12 dB/octave below 1 kHz. between 1 kHz and 3 kHz, it’s about +/- 1.5 dB, followed by a broad +6 dB peak centered around 4 kHz. There is a dip around 10 kHz followed by another peak around 16 kHz. i feel the midrange sounds quite natural on the iphone 3G and this seems to be reflected in the mostly-flat 1 ~ 3 kHz measurement.
Interested in recording bird sounds from various distances (10 ft to 50ft..will the iphone do it? What about attached microphones(inexpensive hopefully)??
My friend says that if you blow too hard in the iphone mic it will break… this isnt true right?
I’m sure the mic isn’t indestructible, but I don’t know what it would take to damage it.
Just curious if you guys could do a similar test with the different dock connected microphones with the ipod touch. not sure if this would even be possible given that they only work with ipods, but if you were to send a signal out of a speaker you know is flat (or at least know how much it’s off by) and measure the response on a prof studio flat mic, with the itouch right next to it and see the difference we might gain a better idea of actual world performance. The thing is I’m getting a touch and trying to decide which dock connect mic I should use (because I’m assuming they’d work better)
Has anyone developed an inverse frequency response to the 3Gs microphone so I can apply it during mixing to yield a ‘flatter’ outcome?
One problem with that approach is that the signal to noise ratio (SNR) deteriorates rapidly below 200 Hz. Amplifying those frequencies (by applying an inverse filter) will not improve the SNR and will leave you with a very noisy result.
Yes Thanks, I understand. Just that I have one recording I am desperately trying to make the most out of it… even if it means the inverse EQ of the responses above 1Khz will be much appreciated.
Are iPhone apps able to detect whether the signal source is the built-in, a headset, or a dock? If so, do Faber s/w products adjust freq. responses for the built-ins or allow users the option of adjusting for other response curves?
“Inquiring Minds Want to Know!”
Yes.
No. (See previous comments.)
Do you have a Griffin SmartTalk that you can test? I’d like to see how its microphone compares to the rest.
Do you have a bigger resolution graph or some raw data for the frequency response of the 3GS microphone in the +18kHz range?
That seems like a peculiar request–what are you looking for?
Im currently dreaming about connecting a phantom powered shotgunmicrophone to a ipod touch 3G for recording my lectures. Like the type of microphones you use for booming in movies.
Is it possible ?
I need to do aproximately 2 hours recording a day, so i will probably need external batteries for the ipod. . .
But has anyone done it?
Best regards from
Copenhagen
You might want to check out the Alesis ProTrack. It uses its own batteries and supplies phantom power.
Has anyone tried the Mikey dock-microfon from Blue Microfones on the iPhone? Looks like an interesting proposition, but I would love some first hand reports and certainly some measurements on the Mikeys freq. response. Anyone?
http://www.bluemic.com/mikey/
Hi, I just purchased signalscope for a new iphone 3gs and I am getting a response near 15 kHz that has to be internal because it happens everywhere. It is actually very narrowband spikes separated by 60 Hz so it looks like modulation of a clock with AC power but is it truly microphonic or say capacitive. It goes away using the iphone headset mic.
Hello Guys,
Sorry to be ignorant but why is the Airplane Mode mentioned in the Mikey Blue information on Lasse’s link above? Will it not function normally with a 3GS as I am looking for the best quality portable mic.
Thanks and happy 2010!
Existing dock connector input devices were designed under Apple’s Made for iPod program, which did not account for the iPhone. The iPhone is a mobile phone, which produces noise that can interfere with audio signals, and it can also be affected by the presence of accessories that were not specifically designed to be operated with a mobile phone. So, the iPhone OS gives you the option to switch to Airplane Mode, so you can operate your iPhone essentially as an iPod to avoid any interference concerns (for the phone or for the audio signals). You can still use the accessory, whether or not you choose to switch to Airplane mode.
To everybody,
what to do to make good measurements using the iPhone 3GS?
which external device(s) do I need?
(I have bought all the Faber apps and a thumbtrack microphone)
I want to use them professionally in a live sound environment.
Dear Ben,
I recently bought the new iPhone 3GS and am wondering what to do to get good measurements.
My 3G got stolen and I already owned a Thumbtacks microphone.
I want to use the software as a professional in a live sound environment.
I own all the apps and looked at the possibilities.
As the bluemic works with the 3GS but only in airplane mode and the external mic input still has the 200Hz cutoff on the 3GS I tend to opt for a Ipod touch as a second device. Has this Ipod touch the same problem with low cut frequencies?? otherwise i could use the Thumbtracks as a mic input and the bluemic or ProTrack as a line input (the Tunewear is no longer available).
Bonus: less worries when it gets stolen again.
gr. KlaasJan
The low frequency rolloff will always be a problem, unless you use an external microphone connected to the dock connector. (You could avoid the low-frequency rolloff on the headset input, by using the Thumbtacks mic with a 1st gen iPhone, however.)
The ProTrack is not highly portable (it’s big) and you have to find a way to secure your iPhone to it, but it does offer phantom power for higher quality external measurement microphones. Alternatively, if you have an existing measurement microphone and a suitable power supply for it, you can use the line-input feature of either the ProTrack or the Belkin TuneTalk. Again, it’s not super portable, but there is no existing pro-level measurement microphone solution that is.
Do i understand you correctly that the Ipod touch has the same rolloff as the 3GS??
An iPod touch with a thumbtrack mic would be small and easy to use.
your solution is to use an external mic trough a doc connector on your 3GS.
(the bleumic has no external inputs BTW),
Maybe the apple iSlate could be an interesting new option….
HAVE YOU TESTED THE FREQUENCY RESPONSE OF THIS USB FEVER MICROPHONE? IT APPEARS TO BE A USB INPUT AND IS LIKELY TO BE AN ELECTRET MIC LIKE THEIR USB FEVER MINI MIC. SINCE ELECTRETS USUALLY HAVE EXCELLENT LOW FREQUENCY RESPONSE, THIS MAY BE GOOD FOR 2G, 3G, ETC IPHONES AND IPOD TOUCHES.
HERE’S THE LINK:
http://www.usbfever.com/index_eproduct_view.php?products_id=1324