You can also use it as a portable cassette player by inserting the batteries and connecting the earphones to the main unit. If you input AUX, you will not be able to check the voice with this product.Please check with the earphone terminal of the connected device. By using digital data, you can listen to audio sources from your computer or MP3 player without the need for a bokecase. Choose between MP3, WMA, and WAV formats.