Here's what Zoom say about the IQ7:
When you're ready to take your iOS audio to the next level, plug in a Zoom iQ7. This compact yet full-featured mid-side stereo condenser mic is perfect for capturing music as well as video with outstanding audio. With the iQ7, you can create great-sounding recordings on your iPhone, iPad and iPod Touch any time, any place.
The iQ7 offers advanced features that allow you to create extraordinary stereo recordings every time. A large front-facing MIC GAIN knob allows you to easily set the optimum input level, and three-segment LED level meters ensure clean, crisp sound with no signal overload.
In addition, a dedicated headphone jack—which doubles as a line output—allows you to monitor your audio during both recording and playback.
Mid-side is an advanced recording technique that allows the width of the stereo image to be varied, even in post-production.
The two microphone elements in the iQ7 include a directional "mid" mic that captures signal coming from directly in front of your iOS device, and a bidirectional "side" mic that captures the audio coming from both sides.
A three-way switch allows you to select between 90° (to focus on sounds coming from the center) and 120° (for a wider image that includes ambience and room signal). A third setting, labeled "M-S," enables you record the audio "raw" and adjust its stereo width afterwards, using Zoom's free downloadable Handy Recorder iOS app.