The TD-25 can play stereo WAV files (8, 16, or 24 bit, 44.1kHz) and mp3 files (44.1kHz, 64kbps–320kbps). If a file matches these specifications but still will not play, it may contain embedded metadata ("tags") that prevents playback. This can happen with files exported from DAWs, other audio programs, or sample libraries.
Re-exporting the file as a new WAV or mp3 file using an audio converter (such as iTunes) typically strips this embedded metadata, allowing the file to play on the TD-25.
If the USB flash drive itself is not recognized or will not format, see [linked article on USB drive formatting] instead. For instructions on importing audio files, see How To Convert Audio Files for Importing.