Six (6) of the sounds were developed by Dr. Jeffrey Thompson, one of the world’s leading experts on sound therapy. Dr. Thompsons’ sounds represent the most advanced approach to tinnitus therapy sounds that anyone has ever attempted with fixed pre-recorded sound tracks. Each sound track has multiple high range frequencies built right into the music so it is more palatable to play - during the day or to sleep with at night. Six (6) other sounds provide nature only" sounds for pleasant masking therapy and customized versions of white noise targeting specifi c and general tinnitus frequencies. Note: Sound Card only works with the S-650 model.