ProLoop (App Store link) is a powerful and flexible loop player for the iPhone and iPod touch.

It can play up to 6 loops simultaneously and besides changing the volume each loop can also be pitched/transposed, reversed, muted, panned, ring/frequency/phase-modulated by any other loop, and synchronized to a masterloop.

Pitch can be smoothly adjusted or quantized to a musical unit such as octaves, semitones or a custom division of an octave. Or put it in sync-mode to automagically fit the length of the choosen masterloop.

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 ever-changing 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 that you can use and play around with, and demo sessions to get you started, but the real power comes by the fact that you can upload your own soundfiles to ProLoop through your web-browser.

ProLoop sells for $4.99.