Many an attempt has been made to clarify these fundamentals of AVS/entrainment. I’ve never made a stand-alone attempt – so here goes…
In music and physics these terms have well-defined meanings. In AVS they have become ambiguous.
The frequencies of primary interest for AVS/entrainment are below the range of typical human hearing, which is loosely defined as 20Hz to 20kHz.
FREQUENCY describes a beat, pitch or tone. The unit of frequency is the Hertz (Hz), from German physicist, Heinrich Hertz. Frequency is measured in cycles per second, where a cycle is the time from the beginning of one repetition of a waveform to the beginning of the next. 1Hz is equivalent to 1 cycle per second (think of a tap dripping once per second). Standard metric prefixes give kHz (1,000x), MHz (1,000,000x), GHz (1,000,000,000x) and beyond. Wavelength, significant when considering echoes and spacial relationships, is inversely proportional to frequency, dependent on speed in medium.
TONE is used as a generic term for any audible frequency or set of frequencies that can carry or form a beat. The tone is often referred to as a CARRIER for this reason. You will see reference to isochronic, monaural and binaural tones in entrainment applications such as Neuroprogrammer or Mind Workstation. A tone is just a tone until it is modulated or controlled, in which case it may become a beat. The sound of a drumbeat is an isochronic – the pitch is the resonance of the skin, modulated by the rate at which it is struck, the beat.
The PITCH is the frequency of the tone. Pitch may also be described in terms of musical notes. Middle A = 440Hz.
The BEAT is the brain rhythm frequency stimulus that is imposed on the tone. An isochronic beat takes a single frequency tone and modulates it (changes its volume) with the beat waveform. Monaural beats are formed when two single frequencies are mixed – the beat frequency is the difference between the frequencies of the two tones. Binaural beats are formed when the two different frequencies are applied to each ear instead of mixing externally – binaural beats do not exist in any measurable form – they are an internal construct.
The beat and tone/pitch can each have different waveforms, creating interesting complex waveforms (Mind Workstation supports this option).
The point to all of this is that you cannot use a simple tone as stimulus at brain rhythm frequencies, below 20Hz. By using any one of the many methods of modulating a higher frequency carrier with the lower frequency beat, this limitation can be bypassed using ordinary audio equipment.
I have seen quite a few guidelines for binaurals scattered around the web – I can neither confirm nor deny their usefulness, but overall I have the impression that they are fanciful in their level of detail. If you can hear the beat form, then it will be doing its thing (which is something other than true entrainment).
For isochronic and monaural, any pitch in hearing range above the Nyquist limit (twice beat frequency) is fine – aesthetics and psychological correspondence to the session’s intent are all that matters. Psychological correspondence? It’s very hard to relax to a siren-pitched beat!
An isochronic beat does not require a tone at all. Amplitude entrainment of a noise track forms an isochronic beat “filled” with noise instead of “tone”.
Fortunately you need to know almost nothing of this to write perfectly excellent sessions, simple or complex. Using the sample sessions in NP3 or MWS as templates, experiment with different pitches and waveforms and see how you respond to them. Add extra tracks. See what you can do with the special effects – hint… echo and reverb in MWS allow you to set times – match periods to significant beat frequencies. If you’re not selling your material, then what works for you is of vastly more importance than any technical or consensus justification/”proof”.
If you decide to write complex sessions for more general consumption then a look at basic audio engineering texts will be worthwhile - waveforms do very strange things when mixed. Taking the very basic “rules” of what beats are good for what and creating distinctive, engaging and effective sessions requires a reasonable overview of neuroscience, physiology, audiovisual engineering, psychology and philosophy. Complex sessions engage the higher processes of the mind/brain in ways that are only just beginning to become evident as repeatable. Complex sessions begin to make possible the highly specific intent implied in much current “hype” marketing. Lucid dreaming, out-of-body and suchlike experiences are made much more accessible. Meditative and contemplative practices can be structured with precision. Side effects like mild headache, anxiety or nausea are considered a small price. “Liking” the session is of no consequence – taking it like straight whisky, just for the effect. But of course it’s not all hard-core – some’s just plain trippy! I’m not aware of anyone else working with session architectures like mine, but I must assume that there are others doing original and creative things and coming up with useful results – I mean to say, we’ve got an almost virgin field in which to stumble upon all manner of remarkable things!
Of course, there’s nothing wrong with simple sessions. They are often more plainly enjoyable than their complex counterparts. For therapeutic purposes and relaxation they are unsurpassed. Simple sessions are ideal with musical or ambient backgrounds, which create many problems for complex sessions.
Happy session building!