While talking on the telephone today, notice the qualities of each caller’s voice. Is their voice high or low pitched, loud or soft? Write down as many characteristics as you are able to discern and then compare the qualities of each caller (You can use this list of auditory submodalities to prompt you). If you find that you are only picking up a few auditory characteristics, stretch yourself to notice the more subtle, less obvious auditory qualities.
See if you can find other ways to sharpen your auditory acuity.