Dialogic ADPCM or VOX is an audio file format, optimized for storing digitized voice data at a low sampling rate. VOX files are most commonly found in telephony applications, as well as an occasional arcade redemption game. It uses a lossy compression algorithm, optimized for voice, not high fidelity. Dialogic ADPCM is an open file format. It matches ITU-T standard G.721, later superseded by G.726.