An ADP file in the context of voice or audio typically refers to a compressed audio file format used on older systems or devices, such as early mobile phones or gaming consoles. It may contain ADPCM (Adaptive Differential Pulse Code Modulation) encoded audio, which is a method of compressing speech or sound data. If you encounter an ADP file, it usually means it's a voice or sound recording that needs specific software or codecs to play properly.