This page contains information that we have learned about iPhone and iPod Touch hardware and accessory input devices. If you have any knowledge that you would like to share, email it to us and we will add it to this page.
*** iPhone 3GS users: Special iPhone 3GS Note Here ***
iPhone Models
There are two iPhone models, the original (we will call it "first gen") and the more recent 3G model. They are very similar, but there are differences when it comes to audio.
The main difference is that the first gen iPhone's built-in microphone works at a maximum sample rate of 8000 Hz, while the 3G built-in mic can run at 48000 Hz. The microphone connector on the top of either model can operate at up to the iPhone system maximum of 48000 Hz. The output cannot run at a different sample rate than the input, so any time that the built-in mic is selected on the first gen iPhone, the output is also running at 8k. This would happen when you are recording, talking on the phone, or running any of our apps that process incoming audio, if you have nothing plugged into the headset jack.
Our apps try to handle this as best a possible, but we recommend using a headset mic (or another line input device) with the first gen iPhone, since an 8000 Hz sample has a maximum usable frequency below 4000 Hz.
We are currently working on updates to Generator, ETC, and FFT that will better accommodate the first gen iPhone.
*** New: Apple has announced the new iPhone 3Gs. It runs 50% faster than iPhone 3G, has double the RAM, and faster graphics. We don't know about sample rates, but we expect it to be similar to the 3G. It will be an excellent platform for our apps.
iPod Touch
We have not done extensive testing as of now, but we do know that the processor in the second generation iPod Touch is about 30% faster than the one in the 3G iPhone.
We have optimized our apps for use with the 2nd gen Touch, with faster sample rates and screen updates, where it has made sense to do this. Specifically, FFT and RTA both run significantly faster on the 2nd gen Touch.
Accessory Input Devices
We have tested a few models of accessories that can provide a line input to the iPhone, by plugging into the dock connector.
We will be releasing our own dock-connector audio interface, which includes a microphone, balanced line input, and line output (stereo or psuedo-balanced). This is the best option available for doing audio and acoustics work on the iPhone or Touch.
iSoniTalk
This is a nice way to break out the headphone feed. It has it's own mic, which appears similar to the iPhone internal mic, and it has a headphone jack that you can use as a line output for our apps. The mic is subject to the iPhone or Touch hi-pass filter, so always set out mic selector to "Internal" with this device.
Griffin iTalk
This unit has a built-in mic, which we have not tested for frequency response. We can say that the line inputs appear completely flat, although we have not tested the dynamic range or linearity. It is possible that limiting or clip-reduction is present in this unit.
Although it will work with an iPhone 3G, it was not designed for the 3G, and so you will get a warning message when you plug it in, asking you if you want to turn on airplane mode.
This unit is shown as discontinued on Griffin's web site.
Belkin TuneTalk Pro
This model has stereo mics, which we have not tested for response. They do appear to have significant low-frequency roll-off.
We have tested the line inputs, and have found significant low-frequency roll-off, starting at about 300Hz. It looks to be down more than 25dB at 32Hz. Also, the full input range of the iPhone line input is not available, as the TuneTalk starts to clip, or perhaps limit, more than 30dB below the clip level of the iPhone line inputs.
Belkin TuneStudio
Not sure if this device is still in production, but they seem to be available.
This device is like a small mixing console, and has several inputs, including microphone inputs with phantom power. It mostly seems to work with our apps as an input device, but not as an output device. Each channel has EQ which cannot be defeated, and of course there are not absolute level settings so it could not be used to hold cal.
Also, in our tests it does not work with iPhone OS 3.0 devices.
ThumbTack Mic
Extremely cute, and useful for iPod Touch users who do not have a headset. We have tested this device. It is very similar in range to the built-in iPhone mic, and also frequency response, although we do see more of a mid-range dip. Any mic that plugs into the headset jack will be subject to the very steep (6dB / octave, more for iPhone 3Gs) highpass filter, and so it should be used on the "Internal" setting with our apps.