A practice of listening. Use as a daily tuning exercise.
Listen to the environment you are in. Notice what sound reaches your right ear. Notice what reaches your left. Notice what is very near, very far, and in between. As you listen to every sound in your environment, try not to judge any sound as good or bad, as music or noise, as important or insignificant. Allow all sound an equality of value; aurally observe the existence of these sound in the field of spacetime where you are.