Good external microphones for the iPhone/iPad are expensive – not the kind of thing you want to buy and find out they are no good! Here’s a comparison of three external iPhone microphones: The Apogee MiC, Fostex AR-4i and Tascam iM2.
They were all tested on my iPhone 4s by recording into the FiRE iPhone recording app at full quality. On the microphones that had a volume adjustment, I adjusted it to be at the top of the green range in FiRE, quite conservative, no chance of clipping. I had the mic placed approx 20cm in front of my guitar sound-hole at the same height in all the tests. The Tascam doesn’t give any indication of levels, the Fostex has 4 LEDs on top to show the levels and the Apogee has a single LED on the front. The single LED on the Apogee seemed to give a better indication of input level than the three LED’s on the FOSTEX because the difference in brightness was easier to discern on the Apogee LED.