Music therapists often use music to facilitate changes in physiological functioning. In order to better inform the selection and creation of such music, this study explored the influence of tempo and dynamic range on heart rate variability. Two guitar improvisations were digitally recomposed to create fast and slow (90 and 60 beats per minute) as well as narrow and wide dynamic range conditions, while all other elements of the recordings were held constant. It was hypothesized that faster tempo and wider dynamic ranges would cause an increase in physiological arousal, indicated by decreased heart rate variability. It was also predicted that participants (N = 32) would perceive selections with slower tempos and smaller dynamic range as more relaxing. No significant differences were found in heart rate variability for either condition. The narrow dynamic range condition produced an elevation in average heart rate, contrary to expectations based upon previous clinical recommendations. Participants did not perceive any condition as more relaxing, but perception of relaxation level weakly correlated to increased heart rate variability. The results from this study suggest that wider dynamic range is not necessarily contraindicated for music for relaxation, and that participant input is important in choosing music for relaxation
