All current iOS devices include built-in microphones. These mics tend to be very consistent from one unit to the next, and are wide-range. However, Apple does include a very steep high-pass filter (which cuts low frequencies), presumably as a wind and pop filter. The low-frequency roll-off for the internal mic in these devices is very steep, on the order of 24dB / octave starting at 250Hz.
However, with the advent of iOS 6, and AudioTools 4.7, we are able to turn off the low-frequency rolloff filter, thereby resulting in fairly flat response. Of course this is still basically a cell phone mic, and the performance is limited. Also, often we find that real-world mics get dirty or damaged in usage and performance degrades over time.
Also, in most of the later models, there is a limiter -- making SPL measurements, as well as more sophisticated measures such as Impulse Response difficult to make accurately. Again, we can disable this limiter (as of iOS 4.3), so we can work around this.
In iOS versions prior to iOS 6, we have compensated for these mics as much as possible, but given the physics of the situation, the usefulness of the low frequency information is limited. We therefore strongly recommend upgrading to at least iOS 6, and the most current AudioTools release.
You can also create your own microphone calibration file, if you would like to override the default compensation in AudioTools.
Also see our comments on MicW.
And, check out our iPad Audio Devices page.
Changes in iOS 5 and iOS 6
In iOS 5, Apple gave us an actual audio session category called "Measurement". This was a huge step forward, even to have Apple acknowledge that audio measurement is a viable subset of audio users.
When using this category, (which we have implemented starting in AudioTools 3.7), the limiter is disabled, and we also have for the first time the ability to control the input gain of the built-in mic. This is a huge benefit, and now we can measure dB SPL levels up to (and sometimes over) 120 dB SPL!
AudioTools now automatically senses whether or not input gain control is available on the device, and when available the input gain is adjusted, in two ranges that are present on the Input Select screen for each module.
Select Low Range for the best performance in the 30 - 90 dB SPL range, and select High Range for the best performance in the 45 - 120 dB SPL range. This does vary a bit by device, but in most cases works very well.
The one exception in the current Apple product line (based on our in-house testing) is iPad2, which does not support input gain control, at least for now.
Although the severe lo frequency cut off filter is still present in iOS 5, Apple has finally given us the control to turn off this filter, in iOS 6. So upgrading is definitely recommended.
As an aside, we had posted a bug report to Apple last year in iOS 5 requesting that the LF filter be disabled in measurement mode, and we did receive an email that this was "corrected" in iOS 6.
Using the Headset Output Signal
The headset connector is a 4-pin connector on the iOS device. The additional pin is for the mic input. If you want to use the output from the headset jack (for example as a pink noise source) while still using the internal mic, make sure your cable has a 3-conductor plug. This will tell the iOS device to leave the internal mic operational.
There are also splitters available, for example by SoniTalk, that provide a 3-pin headset output and also include a mic similar to the Apple mics.
Dock Input - Analog or Digital?
Apple provides audio input on the 30-pin connector. For iPhone 3GS, iPod touch 3, and older models, this input was analog.
Starting with iPhone 4, iPod touch 4, and iPad, these newer models provide only a digital audio input on this connector. This is a high-quality digital audio link, and provides and excellent signal path in and out of iOS devices. There is no analog input on any current iOS devices.
Analog Input Devices
Since the 30-pin dock connector no longer supports analog input, there are no modern analog audio interface devices that can connect to it.
Digital Audio Input Devices
Starting with iPhone 4, Apple implemented a digital audio link in the 30-pin connector, and also now in the Lightning connector. This provides a way to get high-quality professional audio into and out of iOS devices. All current iOS devices use this audio interface method.
Our new iAudioInterface2 connects to the iOS device using digital audio, and provides a phantom-power microphone input with up to 50dB of gain, a second balanced line input, a balanced line output, and a Toslink digital audio output. It includes a built-in li-ion battery system, and can charge the attached iOS devices when the charger is plugged in.
iAudioInterface2 also is tightly connected to our AudioTools app, providing gain control, mode control, and access to advanced features such as impedance measurement.
iTestMic uses the same digital audio link, and also avoids all Apple analog electronics.
Over time, more iOS digital audio devices will become available. We will update our iPad Audio Devices page as more devices become available.
Type 1 & 2 Microphones
See our Microphone Type 1 & 2 Certification page for information about ANSI and ISO specification compatibility.