Gnaural is a multi-platform programmable binaural-beat generator, implementing the principle of binaural beats as described in the October 1973 Scientific American article Auditory Beats in the Brain (Gerald Oster).
It can be used to synthesize sounds that affect the brain. Here’s a demo. It should be listened to using headphones:
The central theme of Oster’s article is that processing of auditory binaural beats within the brain bears distinct differences from that done for normal sound, emphasizing different neural pathways and highlighting different parameters of the sound stimulus.
Oster’s observations inspired a wave of research in to the ways in which binaural beats could affect the brain. One area of research explored how binaural beats could evoke a “frequency-following response” (also known as “brainwave entrainment”) in EEG measures. My personal interest in binaural beats has centered almost exclusively around exploring this entrainment potential as a means of facilitating meditative states. However, Gnaural was designed to be neutral with regard to any hypothesis or application, relying strictly on the fundamental findings as described in Oster’s 1973 overview.
Gnaural is an open source project. Versions are currently available for Windows & Linux, but not yet for Mac OS X.
What are auditory binaural beats?
In 1839, German experimenter Heinrich Wilhelm Dove discovered that illusory “beats” are perceived when pure tones of slightly different frequency are separately and simultaneously presented to each ear. Dove’s insight was to realize that since there is no acoustic mixing of the tones, the perceived beats must exist soley within the auditory system, specifically that part which processes binaural (e.g., “stereo”) sound.
While research in to binaural beats continued after that, the subject was largely viewed as no more than a scientific curiosity. Oster’s paper was landmark not so much for its laboratory findings, but in how it tied-together the isolated islands of research since Dove, in a way that gave the subject a renewed relevance to modern scientific questions.
In particular, Oster viewed binaural beats as a tool with cognitive and medical applications. Cognitively, he felt it could be used to explore neural pathways, and also to address higher-level questions, including how we spatially locate sounds in our environment, and our auditory system’s propensity for selective attention (e.g., the “cocktail party effect”).
Medically, Oster saw potential for binaural beats as a diagnostic tool, both for auditory impairments, and for a broad range of non-auditory subjects. Most notable was evidence Oster showed that a decreased ability to perceive binaural beats appeared to be a pre-onset indicator of Parkinson’s disease. He also presented corroborating data correlating subtle cyclical fluctuations of estrogen in women and their ability to perceive binaural beats.
Notable for Oster’s thesis (that binaural beats are processed in ways fundamentally different from normal hearing) was the fact that binaural beats are percieved even when one of the two frequencies is below the human frequency threshold, and also when both frequencies are below the human volume threshold. This, combined with the brain data available at that time, suggested to Oster that the processing of binaural beats followed different neural pathways in the brain from other auditory processing.
Broadly, the rhythmic influencing of brainwave activity is known as “driving.” And while binaural beats have no monopoly as an auditory driving stimulus, they do have the unusual property of being able to deliver direct auditory stimuli at sub-audible frequencies (below the range of human hearing), by virtue of the heterodyning being simulated within the auditory system.
The reason this is interesting in regard to FFR is that (generally speaking) the spectrum of perceivable acoustic frequencies is well above the frequency spectrum of brainwave activity. Thus, aside from binaural beats, the only means of presenting acoustic driving stimuli is by externally modulating sound (in to waves or pulses whose periodicity falls within the spectrum of brainwave frequencies).
Binaural beats, on the other hand, provide a direct means by which pure acoustic tones can be delivered to directly produce a driving stimulus within the range of brainwave activity. Perhaps even more important (in regard to driving) is that with binaural beats, the driving stimulus arises internally (within the auditory system). This suggests that binaural beats may more effectively induce driving than simple monaural modulation, if only for the fact that the resulting stimuli arises directly within neural pathways that can be measured in the course of gauging brainwave activity.
Gnaural is officially open source, released under the GNU General Public License.