I don't cover tuner apps very often, but this one looked interesting ...

But this one was Audiobus compliant so I thought it should get a mention ...

The Auto-Tune iOS app for vocal pitch correction is available on the Apple App store. Now Antares' world class Auto-Tune ® recording studio technology is available for the local performer to use live, on-stage, using an iPhone or iPad. Alpha Scorpii is pleased to partner with Antares Audio Technologies of Scotts Valley, CA to bring the Auto-Tune technology to the iOS platform.

“With more and more artists bringing iPads on stage for set lists, lyric viewers, and such, it is a great time to bring vocal pitch correction on stage too” says Sue Marvin of Alpha Scorpii. "Auto-Tune iOS is made with the local musician in mind. Whether you are singing lead or backup vocals, trying to reach a difficult high note, or just wanting to make sure you're on pitch, Auto-Tune iOS is a safety net to make sure everything in your performance is in-tune.”

The Auto-Tune iOS app works by connecting the iPhone / iPad between the microphone and the P.A. / sound system using a microphone audio interface device and the appropriate cords. General pitch correction is achieved easily with the default settings to make sure the vocalist is in tune, not singing sharp or flat. More precise pitch correction can be achieved by targeting specific melody notes and/or setting a specific key or scale of target pitches. Meters on the app indicate which note a vocalist is singing and whether they are singing sharp or flat.

In addition to natural sounding pitch correction, a vocalist can apply the iconic “Auto-Tune Effect” using the app, to create that robotic vocal effect popular in hip-hop and pop music. A bypass button on the screen can be used to easily and quickly apply or remove the effect.

Auto-Tune iOS brings professional pitch correction to the iOS platform. Auto-Tune iOS is Audiobus-compatible; it is positioned as a filter effect on the Audiobus; and so can be used in recording situations with other Audiobus iOS music apps.