iPhone Headset Input Options
One of the most obvious ways to get analog signals into an iPhone or 2nd generation iPod touch is through the headset connector. Several options exist for getting acoustic or electric signals into the headset input, which are discussed below. Any of these options will work with the iPhone, iPhone 3G, or iPod touch 2G. The original iPod touch does not have a headset connector with a mic input channel, so it is left out of this discussion.
When making a decision about what to use the headset input for, or what to connect to it, you may want to take a look at the frequency response measurements of the various iPhone OS devices.
Acoustic Signals
Acquiring acoustic signals requires some type of microphone. Several off-the-shelf options exist for attaching a microphone to the headset jack, as listed here:
- Apple iPhone headset–included with every new iPhone
- Apple earphones with remote and mic (MB770G)
- Apple in-ear headphones with remote and mic (MA850)
- SwitchEasy ThumbTacks microphone
- USBFever mini microphone
Standard iPhone headsets can be used for basic sound level estimates with SignalScope Pro, SoundMeter or dB, without any further calibration. Using any other microphone (besides the iPhone’s built-in microphone) will require calibration before meaningful sound level measurements can be made. (dB does not support microphone calibration.)
Original iPhone users will be glad to know that the SwitchEasy ThumbTacks microphone will fit into the iPhone’s recessed headset jack. This is not true of the USBFever mic, however, so an adapter cable will be required for that mic. Another benefit that the original iPhone gains from using these mics is that the full audio sample rate will be available rather than being limited to 8 kHz, as it is with the built-in microphone.
Connecting either of the SwitchEasy and USBFever microphones will preclude the use of headphones, unless some special adapter cable is used (I’m not currently aware of an off-the-shelf solution).
Frequency response measurements of these microphones can be found here.
Electric Signals
Acquiring signals from some other source can be a little tricky for the following reasons:
- The headset microphone input is very sensitive (it expects a low-level microphone signal).
- A bias voltage is present on the headset input to power electret condenser microphone capsules (used by the afore-mentioned microphone accessories).
- The headset input expects to see a particular load in order to signal the OS that an external microphone is present.
Of the three issues, the third one is perhaps the most difficult. To be sure the iPhone OS will select your input signal, you can place a suitable resistor in parallel with your input. One user reported that a 3.3 kOhm resistor dropped the bias voltage from 2.7 to 1.9 VDC. When connecting the headphone output directly to the headset input for some basic frequency response measurements, I have had good success with a 670 Ohm resistor. I have also had success connecting external measurement microphones and accelerometers, using a constant-current power supply, without using an additional resistor.
The best adapter cable I have found for connecting to the headset input is a standard A/V cable, which has a four-conductor mini-plug on one end (for connecting to the iPhone) and three RCA plugs on the other end. To work with the original iPhone, the A/V adapter cable needs to have some of the plastic carved off around the mini-plug, or another adapter cable is required to fit the iPhone’s recessed headset jack.
Sometimes, connecting external signals to the iPhone’s headset jack is the most convenient, portable solution. However, working with dock connector input devices allows for up to two input signals without the complicating issues of the headset input.
It should also be noted that the iPhone 3G rolls off the low frequency response of it’s headset input below 100 Hz.
Hi Ben,
This is a super help – thanks so much for all your work with this. I wanted to ask a related question. I’m shooting video/audio for a music festival next week and will be doing interviews as well as on-site shots of concerts. So as to be as portable and unencumbered as possible, I’m going to try to do all the video and audio work on the iphone 3gs.
If I pick up a decent all-around dynamic omni mic – say an Audiotechnica ATR-50 – and plug it into the iphone via a coupler to the A/V 4-conductor mini-plug you mentioned, will this record ok? Or will I need to put something (a line attenuator?) in between mic and iphone to modify the input signal such that it will record. problem of course is that ill be on location and so wont really have ability to have extra equipment along with me – was hoping to do this with just the iphone and an external mic.
what do you think? possible at all? would appreciate any thoughts on the situation, as am feeling a bit lost in the little writing that’s been done on the audio recording capabilities of the new 3gs.
thanks in advance for any advice…
best
Roger
Roger,
A “decent” dynamic mic may still not be as good as the electret condenser mic in the headset that came with your iPhone (and the ATR50 is not an omnidirectional microphone).
Also, with the iPhone 3GS, unless you use the dock connector for audio input, the low frequencies will be significantly attenuated below 200 Hz. Take a look at the the frequency response plots in related blog posts.
Ben
Hey Ben,
Thanks again for your follow-up advice. I see what you mean about a dynamic mic not being as good as the electric condenser in the iphone, but I’m hoping to get an external more to shove in ppls faces to interview while I’m filming video on the iphone. Otherwise, I would probably just use the internal mic, whose quality is actually quite good.
I went down to J&R Music World in New York this morning to test out some options. I tried out the the ATR50 and had an interesting discovery. The mic plugged into the iphone via the A/V four-conductor miniplug did actually record sound at a decent level, *but* the recording was accompanied by a strange regular metronomic clicking sound. This sounded like some sort of power loop. I’ve uploaded a copy of the recording here – www.norums.com/Memo.m4a.
Any idea what this is and/or if there is any way to get rid of it? Or do you think I am fighting a losing battle?
BTW I just had confirmation from Touchmic and Blue (Mikey) that their microphone products are compatible with the 3GS.
Cheers,
Roger
When connecting external signals to the iPhone’s headset jack, your best bet will generally be to work with devices that were developed under Apple’s Made for iPod program. Anything else can be problematic (and you may not want to risk damaging your iPhone). If the headset mic won’t work for you, another option (though less portable) would be to check out options for dock connector input. The Alesis ProTrack offers XLR inputs and phantom power, but it may not be as portable as you would like.
Sorry, made a mistake. The mic I tested it with this morning to get that clicking sound was the Audio Technica ATR-25 – stereo condenser. The recorded actually didn’t pick up anything fro the ATR-50 – it didn’t even produce enough input to shut off the internal mic…
http://catalog.belkin.com/IWCatProductPage.process?Product_Id=277661 the belkin voice recorder connected to an ipod would work for what you are trying to do. The sound is great and it’s much less expensive. I’m trying to do the same thing, but I want to attach a lapel mic to an iphone 3gs and use the built in voice memo app to record– any ideas on how to do this. I tried a standard 4 connector 3.5 mm av to three RCA cable with an RCA to mono 3.5 adapter and plugged the mic into that with no results. Does the apple av dock cable have any audio in?
++1 again, I would like to do the same as Roger and Isaac.
(sorry its not much of a contribution. Just want to commiserate.)
I’m not exactly versed in audio matters, but as I understand it, recording a signal through the headset input of the iphone 3gs requires a different connector than a standard line-in plug?
Does this mean that a standard unpowered microphone (in particular, this one: http://www.olympus.co.uk/consumer/2587_TP-7_Telephone_Pick-up.htm) will not work when connected to the headset jack of the iphone 3gs? Or perhaps it would work if I use an adaptor cable?
My confusion has reached a new threshold on this topic. Any help would be much appreciated.
The headset input uses a special 4-conductor mini-jack. Your safest option is to use a headset microphone that was developed under the Made for iPod program.
I need a double-sided jack that plugs into the iPhone that has the same 3.5mm plug on BOTH ENDS (with the 3 “stripes”) Any ideas where I might find this?
Try this, Alan: http://www.wiredco.com/3ring-cond-35mm-miniplug-35mm-male-cable-p-348.html
“The headset microphone input is very sensitive (it expects a low-level microphone signal).”
Do you have any specs for this? I’m connecting an externally-powered sensor and want a decent SNR without blowing the input.
“The headset input expects to see a particular load in order to signal the OS that an external microphone is present.”
Have you determined just what this load is?
Thanks!
You can get official specifications by joining the Made for iPod program.
I need to line-in recording using the iphone headphone input, any ways to do that?
The headset jack does not support line-level input. Your input levels will be limited to around 10-15 mV (peak).
@ Isaac, Roger, and Chapito
I used a TRRS breakout cable from http://www.kvconnection.com that takes the iphone headphone jack and breaks it into two TRS plugs. One wired for stereo headphone output and the other wired for mono microphone input. They have the adapter that is the reverse as well so make sure you choose the correct one.
I then connected a microphone that was purchased from http://www.soundprofessionals.com to the microphone input and attached my sennheiser headphones to the headphone output. The mic was an AT831-SP cardiod lapel mic made by audio technica. I believe this mic was made for voice so the frequency response is probably not flat but more tailored for human speech. It was terminated for mono recorders with a TRS plug wired for mono. Works great. Good sound levels in my recording apps (used for voice recording), using the iphone as a phone, and using skype as well. Very loud sounds may overdrive it since there is no built in attenuation. You could add a simple inline attenuator or “volume control” if needed. I have not needed to in the environments I have been using it in. Sound has been excellent!
Great solution so far. I also use it with my new sony m10 which will record sounds below 200hz. Too bad about the iphone 3gs mic input roll off for recording but I am sure it helps with mic input for voice apps.
I am sure other similar quality lapel mics would work as well. I have an AT-943 wired the same way I will try next. It is an omni capsule with a flatter freq response.
Can’t wait till someone comes out with a line in device that allows us to use our own clean preamps and doesn’t roll off the low freqs. Maybe someday.
Hi there, hopefully this isn’t a dead forum.. I’m trying to create an affordable RTA system that I can use for the many different venues that I run sound in. It would be awesome to be able to use a DBX RTA-M real time analysis mic or even the output of my Radioshack Digital SPL meter to go into my 2nd generation iPod Touch. This “Bias Voltage” that you mention.. is that Phantom Power? Do you have any idea about the loads that these sources may present to the touch’s inputs? Do you think that the frequency response would be accurate enough for my line of work? I’m willing to sacrifice some accuracy for the sake of mobility Thanks!
You might want to check out the Alesis ProTrack for phantom power. That would allow you to use your DBX mic (plug it right into the ProTrack).
No.
If you use the ProTrack with your DBX mic, that will probably meet your needs. The ProTrack isn’t the most portable solution, but it’s arguably the best one for phantom power.
I was hoping to setup my JVC digital video camera and take the composite video output and display it on my Iphone screen. Is it possible to plug the video output from the camera into the headphone jack adn display the video on the iPhone? Would it have to go in thru the sync cable? Would it require any additional software?
Let me know if you think it is possible. Thanks
There is no video input on the iPhone.
Hi Ben
do you know if its possible to plug a sony ECM-DS70P electret condenser microphone into the headphone jack of the iphone. Its a great mike that I used with minidisc, but it only has 3 conductors not 4 – do you know if there an adapter to make this work or not?
Jonathan
I don’t know of an existing adapter. You might want to see if it’s worth your time to acquire the components and make your own adapter. I can’t say for sure whether it would work, but if you want it badly enough, it might be worth a try.
Are you part of the “Made for iPod” “Works for iPhone” program? I’ve applied and been denied, any idea where I could find the info needed to use the dock line-in? If your answer is to join the made for iPod program, any hints on getting approval? It’s hard to show them a product when you can’t get the specifications needed to make one for them that works.
The Made for iPod program is the only official way I know of to get access to iPhone/iPod dock connector specifications. You might want to contact the MFI folks directly to get a better feel for why your application was denied.
Ben, I have a real nice fm portable receiver. How can I get the signal coming from the earphone jack into my iphone six plus mike jack without blowing my phonw up. I want to record the output. Can this be done?
Thanks for a really great article.
I’d like to know at what SPL does the original iPhone mike input clip–How loud a sound is needed to drive the iPhone preamplifier into clipping?
As ben stated, the mic inputs are built to power electret mic
capsules directly (they use about 500uA). When the microphone
powers up and “pulls” the mic line voltage partially toward common, the unit senses it “has” an external mic connected. The function switch(es) on a headset short this connection directly or through series resistors to common to signal the unit that a switch is pressed, and upon releasing the switch, they allow the mic capsule to power back up and work again. Use of other mic types externally means you have to simulate the electret capsule load on the mic input AND AC couple your microphone so as to not run current through a dynamic mic or a coupling transformer inside of your external microphone.
I have found electrets rated at -64db tend not to overload the
input whereas the venerable WM-61A and others rated more sensitive
will.
All in all it’s a great little mic input from Apple but is not a
good prospect to make line level or pro caliber inputs possible which is why Apple designed in better options.
I suppose it is human nature for us to attempt to see just how
much we can get out of such a cool gadget…
Hi,
I bought Riotfx and followed the instructions on the app company’s website to create a cable that can connect my bass guitar to the iPhone.
However whether I’m plugging the yellow, red or even white RCA to my bass, I can never get any input from
the bass to the iPhone.
I have emailed Riotfx for help, but would like to try my luck here and ask if anyone might be able to suggest Amy possibly solution toy problem?
Thanks in advance
Wendy
Wendy,
As indicated in the article, above, the iPhone needs to see the right load on the headset mic input, before it will select it as the active audio input for your apps. It looks like you would have a similar problem with the PRS Guitarbud cable, since that cable does not look like it was developed under the MFI program (Made for iPod) either. Sometimes, you can get the iPhone OS to select your headset input cable, by plugging it in very slowly, but that can get frustrating since it often doesn’t work.
Another issue you may want to consider is that the headset input rolls off the low frequencies of your input signal, which would be particularly troubling for a bass guitar. (There is some discussion of the low-frequency rolloff elsewhere in the iPhone section of this blog.) Your best bet might be to work with a line-input accessory connected to the dock connector (like the Belkin TuneTalk, or similar, which is also discussed in other posts within this blog).
Ben
Thanks for the fast response Ben!
I tried connecting both my bass and guitar but neither worked so I don’t think the missing input is related to the roll-off of lower frequencies.
Did u mean that I need to get a cable that’s created under MFI so that I can be sure it’ll work?
I’m considering placing order for Protrack since I can’t get it in Singapore, but is there a cheaper alternative that can work like Protrack?
Thanks,
Wendy
Yes. You can get a custom cable to work, but you have to know enough about the iPhone’s headset jack behavior (Apple makes the relevant specifications available via the MFI program).
You could get a Belkin TuneTalk, or similar iPod microphone with line input, for considerably less than a ProTrack. You’ll also need a cable with a mini-plug on one end and a 1/4″ plug on the other end for your bass.
Hello,
i’m reading this article with great interest. i’ve been thinking about doing something for my iPhone, and i have posted at various places already, with no luck … Basically, i’d like to be able to plug my guitar on the iPhone, and in the voice recorder record it, for example, instead of using the internal microphone.
But the big problem is that i’ve opened a senheiser handsfree kit, sadly my electronics skills aren’t sufficient for me to understand what would be the required circuitry for this to successfully work…
So far, i have bought 4-contact 3.5mm male jack (To go into the iPhone slot), and then one 3.5mm jack female stereo (For my headset) and a 6.5mm female jack mono (For my guitar). I’ve soldered directly everything together using common-sense logic, and i’m actually only having the headset working… But the iPhone doesn’t actually seem to “detect” that there is a mic on my circuit, and keeps using the internal mic… i believe the 3 very small components on the senheiser PCB were designed to allow the iPhone to “know” there’s a mic here.
Can anyone please help me with such project? i’d be glad to help myself anyone willing to do so, by offering beer, coffee, or similar help in my skill domain 🙂
Thanks a lot,
Pierre.
Note: i’m very sorry if i’m making some typos or mistakes, i’m not an english native-speaker.
Hi Ben,
Thanks for your feedback. Actually what I want to do is to use the iPhone/iPod touch audio input to interface an external sensor (e.g. temperature,cardiac signal). I was wondering if you can provide me with electrical characteristics of the audio input such as max/min input voltages and currents,offset(bias) voltage etc. If you don’t have this information, I would be very grateful if you kindly let me know where to find it.
Thanks in advance
Hi,
I have an I phone 4 for which I am currently designing a headphones cable (3.5 4pole jack on one end, two RCA (left & right) for the headphone cups, and one sub-miniature electret microphone connected to ring 3 and sleeve of the 4 pole Jack). Now the problem is that even though the electret moicrophone gets recognised (particular load requirement’s met to signal the OS that a microphone is connected), I get weird clicking/ cracking noises in my recordings, pretty similar to an old vinyl. They are similar to the rhythm of a heart beat, going CLICK.click….CLICK.click….CLICK.click…. Any ideas why that is? I can hear the stuff I am recording but as I said these are accompanied by these load annoying noises. The mic needs a 2-10V power supply for its internal pre-amp, so, considering the bias voltage delivers 2.7V then that should be sound (excuse the pun), or not? Another electret lapel mic that (one without external power supply) I bought of ebay worked absolutely fine. It was advertised as working with the Iphone, Ipod etc. I opened it and found the FET, and three resistors (1 bigger and 2 smaller ones). I know that there needs to be at least one resistor in those mic circuits (often a 2.2k resistor) to set the output impedance, but what are the other 2 smaller ones for? Does apple have resistor coding for the headphone jack too? I know that the dock connector uses resistors on pin 21 for identifying different accessories (e.g. 1MOhm for belkin auto adapter). I am very confused about these clicking noises. I would really appreciate if someone could help as I am not able to find any more information on the internet.
Thanks in advance!
Philipp,
Your best bet for developing iPhone accessories, including for the headset jack, is to join Apple’s MFi program.
Ben
Sorry
I forgot to mention the microphone’s specifications:
# Sensitivity: -44 dB (+/- 3 dB)
# Output impedance: <2.2 kΩ
# Directivity: Omnidirectional
# Current consumption: 60 dB
# Nominal operation voltage: 2V
# Max operation voltage: 10V
To me they look like it should work no? just not sure, whether the level is low enough?
Is the clicking noise I hear what JB Tompton refers to as preamp clipping? and is that happening, because the sensitivity is not low enough (lower than -64db better)?
Thanks in advance!
Ben,
I am hoping to use my ipod touch 4G and your app signal scope pro
to take some readings on rotating machines with an external accelerometer. Could you describe in detail or with pictures what I would need to make this work.
Thanks
Mark
Hi, i need some help, i need to conect a video signal, from a cctv camera in order to analize the signal, if have noise, etc. What can i do? Is there something i can do? Thanks.
hi, i need to analize a video signal, 1 Vpp, what options do i have with the iphone? thanks.
I’m not aware of any options for analyzing video signals.
I’ve constructed a scope probe of sorts, using back to back diodes to ground (limits the input to 1.4v), then two 10K resistors as a voltage divider (limits the output to 0.7v). In addition, you can pad down the input with another resistor (experiment to find a value that appropriately attenuates for your need) so you don’t see the clipping action of the diodes and keep a nice clean signal.
You can then test the cable against a known signal level and label it with it’s known attenuation.
The iphone seems to be fine with this circuitry and sees that an external mic is connected.
Hi Jerry,
Do you have a picture of you probe setup? I’ve been trying to make a probe to measure rotating objects using Rise and fall of a magnetic field. Have had some luck but am getting a lot of noise through – assume it is from the bias voltage?
Thanks for your help
Mark
I have what may be a simple 3.5mm jack question, but relative to my 2009 BMW 328i. The car ‘does not’ come with a USB connection (which is a $400 add on) but I’m wondering (wanting) to play my music from my iPhone 4 through the speaker system. The car does have a 3.5mm AUX jack in the console, so if I do a male to male 3.5 between my phone and the AUX connection, can I play back through the internal speakers? I’m not looking for control on the radio system, I’m okay with just play back through the speakers. Words of wisdom please.
Hi
I want to ask about the maximum voltage and current that is allowed for the headset input.
Cheers
What’s the current position for analogue input through the mic port on the iPhone6…?