The most basic rhythm is generated by taking a pencil and striking a hard surface. If you strike the surface 3 times a second you have created a rhythm of 3 Hz (where Hz is the scientific unit for cycles per second). This type of rhythm (example here) is not very useful for RAS. If instead you take a steady tone of say 300 Hz (300 Hz tone) and gently turn that on and off 3 times a second you will get a rhythm like this. This type of gently turning on and off the 300 Hz tone with the 3 Hz rhythm is called modulating the tone with the rhythm.
Modulating the tone by gently increasing and decreasing the volume is called amplitude modulation (AM - like the old radio stations). There are two other forms of modulation: frequency modulation (FM - like the newer radio stations) and phase modulation (PM - used in high frequency commercial applications). In FM rather than the tone getting louder or softer the frequency of the tone changes with time. In PM one hears the tone first in one ear and then the other. These three forms of modulation (AM, FM and PM) are methods of generating rhythms from a given tone that are useful for RAS.
One other method for creating rhythms from a given tone uses binaural beats (BB). If the left ear hears one tone and the right ear hears a slightly different tone the brain combines the two together and the brain detects the difference of the tones. An approximate example (you would have to listen to a stereo sample with headphones to actually hear the binaural beat effect) is here. The use of BB for RAS was first popularized by Robert Monroe of The Monroe Institute.
The only other factor affecting RAS is based upon whether or not one consciously hears the rhythm. At first this does not seem to make sense. Yet the pioneering work of Dr. Paul G. Swingle (Professor: University of Ottawa, Lecturer: Harvard Medical School) has clearly demonstrated that a sound can be covered or "masked" with a properly designed louder sound such that a person cannot consciously detect the underlying sound and yet the nervous system perceives it. Therefore, whether or not a rhythm is "masked" by a louder sound and the type of masking sound also influences the neurological response of RAS.
In conclusion, the variables influencing the audio-neurological coupling in RAS are the tone, amplitude and frequency of the rhythm, the method of modulation of the rhythm and the presence or absence of a masking sound, and if there is a masking sound, its structure. These appear to be all of the factors influencing RAS.
• Why investigate rhythmic audio stimulation?
• EEG data obtained while developing the RAS-1 CD.
• Information and listening directions for the RAS-1 CD.
• Information about the author.
Please note that I have NO training in the medical profession, that I make NO claims of medical competence and that I am TOTALLY incapable of rendering any medical opinion. I am trained as a scientific researcher, having worked predominantly with the growth, processing and characterization of thin films. My area of greatest expertise was in ultra-high vacuum surface spectroscopy. I approach the analysis of rhythmic audio stimulation in an analogous manner to my spectroscopic investigations.