AT3

AT3 is a sound format used in Persona 1 PSP. It was developed by Sony Computer Entertainment for the Sony PlayStation Portable. It is succeeded by AT9 on the PlayStation Vita. Usage ranges from non-looping sound effects and voices to looping background music. To make AT3's, you should use a sample rate of 44100 hz.

AT3 Tools
Tools to make AT3's using .BAT files. You can download them here.