TrapCode’s ProLoop is a looper for iOS that lets you work with up to 6 loops simultaneously.
In addition to changing a loop’s volume, each loop can also be pitched/transposed, reversed, muted, panned, ring/frequency/phase-modulated by any other loop, and
synchronized to a master loop.
Pitch can be smoothly adjusted or quantized to a musical unit such as octaves, semitones or a custom division of an octave. You can also put it in sync-mode to automatically fit the length of the chosen master loop.
The sync offset can be adjusted to have loops sync at other positions than their start, and the sync can be turned off individually to allow the loops to have different lengths to create layers of soundtextures.
There is also a Freeze FX that lets you temporarily “freeze” a loop with adjustable grain size and position.
You can control all the loops in real-time, and multi-touch will let you adjust several parameters simultaneously, for example crossfading by changing the volume of two loops at the same time.
ProLoop comes bundled with loops and demo sessions to get you started. But you can also record your own loops straight into ProLoop, upload soundfiles to ProLoop through your web-browser or paste audio into ProLoop.
ProLoop is $5.99 in the App Store.
Note: ProLoop has been around awhile, but this video intro is new.