The GO:KEYS 3 IN can play back audio files stored in the SONG folder* on a USB flash drive. Audio files must be in WAV: 44.1 kHz, 16-bit linear format / MP3: 44.1 kHz, 64–320 kbps.
*When you format a USB flash drive or perform on the unit, the following folders are created. For details on formatting, see "What kind of USB flash drives can I use?".