iFixIt has uncovered one of the secrets of the iPhone 4's excellent noise cancellation -- which might have flown under the radar because it was so good.
Apple built the iPhone 4 with two microphones for noise cancellation. Its second mic, located near the headphone jack, is for FaceTime calls and to suppress background noise.
iFixIt couldn't positively ID a 3 x 3mm chip (labeled simply "10C0" above) that it found during iPhone 4 teardown last summer, but almost a year later, part of the mystery has been solved. The chip's manufacturer has been identified as Audience -- the same company that built the A1026 voice processor found in the Nexus One (below).
Chipworks solved the mystery by "decapping" the chip which revealed an "AUDIENCE" die marking inside the chip, shown magnified below.