The iPhone is capable of making remarkably good recordings, but its built-in microphone is not. One solution is the Mikey Digital, from Blue Microphones.
As the name implies, the Mikey is a digital microphone that attaches to an iPhone or iPad to add much higher recording quality. As some users have noted online, Mikey Digital will not work with an iPod Touch; that device requires Mikey for iPod, which is no longer made but can be found online.
The technical elements of the microphone are two pressure gradient condensers, a design that captures extra detail. A cardioid microphone, it captures sound in a vaguely heart-shaped pattern that picks up most of the sound from the front, and some from the sides.
The microphone has three gain settings - automatic, low and high. Automatic is for things like lectures, which have quiet passages for which the microphone can adjust; quiet is for distant sounds, like bird calls; and the loud setting will keep the sound from overloading at concerts. Three indicator lights flash red if the microphone is overloading.
The Mikey, which lists for $100, also has a 3.5-millimeter input so a midi instrument or guitar can be plugged in. This accommodates a higher quality recording, in stereo, but an instrument and voice cannot be recorded at the same time. A multitrack recording app, like Garage Band or the free app Jammit, is needed to mix instruments and vocals.
If there is one quibble from a test, it is that the microphone may be a little too sensitive. If I adjust my grip on the phone while recording, that comes through loud and clear. Also, recording outdoors, a breeze sounds like an explosion.
