AUTO is the default transparency setting. When listening to music and having the transparency set to AUTO, you will hear music only. Should you pause music, transparency effect will be activated and the surroundings will be heard, enabling you to have a conversation with a person without taking your earphones out of your ears.
If set to OFF, audio transparency effect will be off, and so surrounding noise will be kept out.
In ON mode, the noise from your surroundings will be heard through the earphones, also when listening to music.
In the Earin M2 app you are able to fine tune the audio and transparency settings to your liking. For example, to hear surrounding noise more clearly, take up transparency volume to maximum, as well as "far" setting to maximum.