The program is very responsive and registers all notes exactly; I tested the tuner with my E tuning fork and it was perfect!
– Tom Pace
I love this app! Blows away any of the other tuners on the app store. Just as accurate as my inline Korg Pitchblack!
The tuner works with the built-in microphone on the iPhone, and with any audio that comes in from an external source, such as the microphone on a headset, on the iPhone and iPod touch second generation. The built-in pitch pipe lets you play a reference tone for tuning by ear.
For best results, plug in a headset with a microphone and position the mic close to the instrument. Then pluck a string with your finger. The level meter should light up when it detects a signal, and if the same pitch is held for long enough, the confidence meter will light up. The target ball should grow bigger, and when it is positioned in the center, your note is in tune. If you are too high or too sharp, the ball will show up towards the top of the screen, and if you are too low or flat, it will be near the bottom.
For guitars and other similar instruments, it is best to "Tighten up," which means you first loosen the string below the pitch you want, and then tighten the peg to the desired tuning.