The invention generally pertains to a hand-held computing device. More particularly, the invention pertains to a computing device that is capable of controlling the speed of the music so as to affect the mood and behavior of the user during an activity such as exercise. By way of example, the speed of the music can be controlled to match the pace of the activity (synching the speed of the music to the activity of the user) or alternatively it can be controlled to drive the pace of the activity (increasing or decreasing the speed of the music to encourage a greater or lower pace). One aspect of the invention relates to adjusting the tempo (or some other attribute) of the music being outputted from the computing device. By way of example, a songs tempo may be increased or decreased before or during playing. Another aspect of the invention relates to selecting music for outputting based on tempo (or some other attribute). For example, the computing device may only play songs having a particular tempo. Yet another aspect of the invention relates to both selecting music based on tempo and adjusting the tempo of the music.