iPhone Microphone Frequency Response Comparison

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

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:

iPhone Headset Microphone Frequency Response Comparison

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…

59 comments

  • Darren

    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

    • ben

      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

      • Kshitij

        Ben,

        When you say 48 kHz, you mean the DAC clock frequency ? Do you have any reference which mentions this number. Have been looking for this for a while..trying to emit 40 kHz ultrasound using iphone.

        Best,
        K

        • ben

          K,

          The sample rate is 48 kHz. To generate a 40 kHz tone with an audio device, you would need a sample rate of 88.2 kHz or 96 kHz (or higher). The iPhone’s audio hardware may be capable of operating at those sample rates, but our apps don’t currently support that.

          Ben

  • Howard

    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?

  • Frédéric

    I would be interested to see the same comparison for the speaker. Do you have this or could you generate this?

    • Daisuke

      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.

  • Jerry Bortman

    Interested in recording bird sounds from various distances (10 ft to 50ft..will the iphone do it? What about attached microphones(inexpensive hopefully)??

  • Nintendogs 2

    My friend says that if you blow too hard in the iphone mic it will break… this isnt true right?

  • Nicholas Finn

    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)

  • solo

    Has anyone developed an inverse frequency response to the 3Gs microphone so I can apply it during mixing to yield a ‘flatter’ outcome?

    • ben

      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.

      • solo

        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.

  • Walt

    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!”

    • ben

      Are iPhone apps able to detect whether the signal source is the built-in, a headset, or a dock?

      Yes.

      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?

      No. (See previous comments.)

  • Eric

    Do you have a Griffin SmartTalk that you can test? I’d like to see how its microphone compares to the rest.

  • Will

    Do you have a bigger resolution graph or some raw data for the frequency response of the 3GS microphone in the +18kHz range?

    • ben

      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?

  • Mads

    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

    • ben

      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?

      You might want to check out the Alesis ProTrack. It uses its own batteries and supplies phantom power.

  • Lasse

    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/

  • Bob

    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.

  • Bonnie

    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!

    • ben

      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.

  • KlaasJan

    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.

  • KlaasJan

    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

    • ben

      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.

      • KlaasJan

        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….

  • FERGUS SMITH

    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.

  • Jeff

    Any microphone response testing done with the new iPhone 4 to see how it compares?

    Have you tested Signalscope Pro on an iphone 4 with OS 4.1 to check compatibility?

    Thanks.

    • ben

      Any microphone response testing done with the new iPhone 4 to see how it compares?

      Yep.

      Have you tested Signalscope Pro on an iphone 4 with OS 4.1 to check compatibility?

      Yep.

  • Peter Green

    Could you tell me what is the highest frequency that the 3GS & iPhone can receive, please?

    • ben

      Our apps operate the I/O at 48 kHz, which yields a theoretical upper bound of 24 kHz. Frequencies close to 24 kHz will suffer greater attenuation due to the antialias filters in the audio codec.

  • Bilal

    Hi,

    Very interesting article. Please could you confirm whether you tested the lower frequencies, i.e less than 20 Hz, or is it just an extrapolation. Also, I would be grateful if you could explain the y-axis notation i.e.dBFS/FS. I am only familiar with dB

  • Sharron Clemons

    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.

  • Simon Logan

    Hi Ben,

    How did you get the nice smooth graphs you show above? When I measure a sweep or white noise (generated from SignalScope Pro) in the FFT analyser, the graph is much more spiky across the entire frequency range.

    Thanks,
    Simon

    • ben

      Simon,
      Measuring microphone response is not a trivial task. Also, the measurements shown above were all made relative to a lab-grade microphone that meets or exceeds the specifications for a Type 1 sound level meter.
      Ben

  • Simon Logan

    Thanks Ben. I’ll need to do some more playing around with this.
    Simon

  • Pingback: iPhone Microphone Frequency Response Comparison « twenty thousand hertz

  • Pingback: Tomlinson Holman To Head Up Apple Audio? | The Sonic Spread

  • Oliver Tangen

    Hi Ben

    Do you know if the mic on the headset that goes along with the iPhone 4 is any better? Could you do a test on the built in mic on iPhone4 and the headset?

    I’m trying to find the best way to tune a piano with a good tuner, but the tuner I currently use seems to have problems knowing what octave/frequency I’m playing. Ex. it mixes up a A3(220Hz) and A4(440Hz). Any suggestions? And yes, I’m actually tuning pianos with my iPhone and it works! 😉 But the built in mic on a HTC Desire I tried was so incredibly accurate so I’m considering switching over to that one..

    • ben

      Oliver,
      Check out the iPhone 4 article in the iPhone category.
      Regarding your tuner, the low frequency attenuation of the iPhone 4 may affect the lowest octaves, but you also need to consider the quality of the tuner software.
      Ben

  • Pingback: Tick Talk » Kello Featured in iW Magazine

  • Tai

    Good day!

    You mentioned about the anti-aliasing filters that begin to roll off the high frequencies somewhere between 20 kHz and 24 kHz. So will the phone still be able to receive frequencies above the 24 kHz range? I read somewhere about it being able to detect to as high as 48 kHz. True?

    What will be the frequencies accuracy range?

    Thank you.

    Thanks alot!

  • Mike

    Hi ben,

    At this time with iOS 5.x and the 4S, is there any way in the iOS SDK to internally turn off or alter the internal mic HPF to extend the low frequency response for your measurement programs?

    Just curious.

    Thanks,
    Mike

    • ben

      Mike,

      I wish there were. We need more people to tell Apple how important this is to them.

      Ben

      • Mike

        ben – thanks for the reply. I will let apple know my feelings, for what that is worth.

        it would be nice if developers could tweak the mic for full range response in their apps for whatever they desired. i dont understand why apple would restrict this if it is a software filter.

        do you know for sure if the HPF is in software or is it in hardware on the PCB?

        thanks again,
        mike

  • Mike

    hi –

    Is there any way to alter/acess the HPF for the iphone microphone in the iOS5 SDK?

    Im curious if the bass response for your sound meter apps can work at an extended bass range.

    Thanks!
    Mike

  • Henrik

    Hi

    Does anybody have experience with the micW i436?

    Thanks

  • Stijn Willems

    Super posts. Do you happen to have the respons for the 4 family (4 and 4s).

    Dreadfull to hear that bandwidth is restricted in the lower erea’s. Would also find it very usefull to be able to experiment with that frequency range.

  • Dick

    Great posting, it finslly explains why my iphone 3g is great for voiceover stuff, very rich bass tones. Funny you have to go backwards to get the quality you need.

  • Pingback: Apps para sonidistas | PandaSonora

  • Pingback: Ultrasound iphone (Shopkick signal technology) | BlogoSfera

  • Pingback: Твоят iPhone се подслушва! | Глас народен

Leave a Reply

Your email address will not be published. Required fields are marked *