While a session is running, the session programming controls most of the operation of the system, although some features may be left to operator control. Sine wave sound refers to pure tones consisting of a single frequency. When you play a musical instrument, the notes have a fundamental frequency and many harmonics. The result is not a sine wave, but on most instruments the result sounds pleasing. Although nature sounds are not designed with certain frequencies in mind, the repetitive sound and light pattern are soothing and work well for quiet entertainment.
Tempered scale is the musical scale used in modern western music.
This approach has advantages in playing music in different keys, but does not make chords come out as well as they could. An interesting alternative is the Just scale used in some light and sound systems. Tone refers to the type of sound stimulation used. Pulsed surf - a surf sound pulsed at the selected frequency, with the selected duty cycle. Pulsed chord - a chord with controllable base pitch and tone separation, pulsed at the selected frequency and duty cycle.