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• Beats are the amplitude variations that occur when pure tones close to each other in pitch are mixed. When tone pitches are far enough apart, the result of mixing tones is consonance (sounds OK). As the mixed tones get within an octave of each other, they sound good only if the tones form good chords. When they get still closer, the effect shifts to beats. A trigonometric formula, long since forgotten by most of us, expresses the addition of two pure tones as:
  sin(a) + sin(b) = 2*(sin((a+b)/2)*cos((a-b)/2)).
  Interpreting the formula, beats are perceived as the average pitch (a+b)/2 modulated (pulsed) at the difference frequency (a-b). If you are paying close attention and noticed the disappearing 1/2, cos(a-b)/2 has two amplitude peaks per cycle, so the modulation is perceived to be at frequency (a-b) not (a-b)/2. When you listen to a mixture of slowly changing tones on a dual binaural beat instrument, fascinating beat effects are heard.
  
• Binaural beats result when pure tones at slightly different pitches are heard by the two ears. The effect is different from a mixed tone beat phenomenon, because the tones are heard and processed separately by the auditory apparatus. Our mechanism for localizing the source of a sound depends on detecting differences of arrival times of the sound waveform -- two tones of the same pitch but at different phases will be perceived as being inside the head, closer to the ear in which the sine wave peaks first. Tones of slightly different pitches appear to have constantly shifting phase, and the source appears to move back and forth within the head at the rate of the difference of the pitches. This is commonly but inaccurately described as "hearing the difference frequency". You can experiment with this effect with a light and sound machine that generates controlled sine wave binaural beats -- beware of machines that attempt binaural beats with square waves (tones with lots of harmonics) -- the trigonometry in beats gets very confused.

• Brain waves are the voltage patterns generated by the brain. The brain contains some 100 billion neurons which operate by generating and passing electrical signals. The summation of all this electrical activity results in signals that can be detected and recorded outside the brain. In analogy to the recording of the activity of the heart in an electrocardiogram (EKG), the recording of the brains activity is called an electroencephalogram (EEG). The EEG pattern is popularly referred to as "brain waves". Brain waves appear as irregular, somewhat repetitive waveforms, and are a mixture of many frequencies from less than 1 to more than 40 Hertz. Different brain wave patterns have been found to be associated with different states of awareness. Several frequency ranges have been identified and given names by neurologists: (Table taken from Megabrain Communications, with permission)

• Cautions (This material was taken from the Mind Machine Buyer's Guide, courtesy of Neuro-Technology Research). For "normal" individuals, light and sound stimulation has been proven to be extremely save and beneficial. However, there are a small percentage of individuals with undiagnosed photic epilepsy who experience their first seizure when exposed to pulsing light. Flashing traffic lights, video games, emergency vehicle lights, and dance hall strobe lights have all initiated seizures in such individuals. Therefore, if you experience any uneasiness or nausea during your first light and sound experience, take off the glasses immediately and end your session. Consult your physician for a diagnosis and proper medical prevention. Also, seek your doctor's supervision before using a light and sound device if you: have ever experienced any form of seizure disorder or epilepsy; have ever suffered any type of head injury or concussion; are presently or have recently taken prescription or illegal psychoactive drugs, such as barbiturates, tranquilizers, or stimulants of any type; are sensitive to bright or pulsing light, or find that such light can produce headaches or other discomforts; have a pacemaker or suffer from any form of cardiovascular problems including cardiac arrhythmia's or other heart disorders; have a history of mental disorders and/or hallucinations; suffer from any major health problem. Microfirm makes no medical claims for any of its products. We advise you not to use a light/sound machine to try to heal yourself. They are a powerful self-improvement tool and can help you achieve deep states of relaxation, but they can in no way replace the knowledge and expertise your physician or other health care professional provides.

• Chords are combinations of tones that (hopefully) sound harmonious. Harmony occurs when the fundamental pitches of the tones are in ratios of small integers, such as 2/1 (octave), 5/3 (sixth), 3/2 (fifth), 4/3 (major third), or 6/5 (minor third). Most people hear tones closer than a minor third as dissonant. When tones get still closer in frequency, beats occur.

• Download is the process of sending sessions from a PC computer over a COM port to a light/sound system. This allows new sessions to be installed easily. Many Photosonix products feature downloading.

• Dual binaural beats is a tone selection with two binaural beat generators running at the same time. Each ear receives two tones, so you hear chords or a beat interaction in each ear, plus the four different binaural beat offsets (each of the two left ear tones against each of the right ear tones). This may seem complex and confusing, but it sounds great -- dual binaural beats with pitch ramping are a fun medium to compose in and listen to.

• Duty cycle refers to the portion of a stimulation cycle that the light or sound is "on". For example, a duty cycle of 40% means that the stimulation is on 40% of the cycle and off for 60% of the cycle. Some light/sound machines provide duty cycle control and it does have an impact on the resulting sensation.

• Features of light/sound systems include the number and variety of the built-in sessions, the number and range of the controlled stimulation parameters (frequency,volume, intensity, tone, pitch, phase, duty cycle), starting and stopping sessions with soft off/on, an audio synthesizer with sine wave sound, whether or not the system permits the user to create custom programs, whether or not sessions can be downloaded from tape, CD, or a personal computer. All of these features should be considered when deciding on a personal light/sound system.

• Fill-in-blanks is a technique of creating light/sound programs by selecting one of a number of available program profiles, and specifying the frequency range and control options to be used. Thus a custom program can be created with four menu selections. Exclusive on the Nova Pro.

• Frequency is properly the rate at which any periodic event repeats, but in light and sound machines it is used more specifically to refer to the primary rate of visual and auditory stimulation -- to the eyes, it is how fast the lights are flickering, to the ears, it is how often the sound is pulsed on and off, (pulsed tones) or how often the amplitude is modulated (binaural beats). Frequency, like pitch, is measured in Hertz. The frequencies of stimulation in light/sound systems are in the brain wave frequency range.

• Hertz used to be called "cycles per second", meaning the number of times a repetitive event occurred per second. Then someone noticed that physicist Heinrich Hertz (1857-94) had no measurement unit named after him, so he was appropriately immortalized, giving opportunities for bad puns: Crank up the frequency till it Hertz. In sound, Hertz is probably number one, but amplitude is a close second and tries harder.

• History: The effects of flickering light stimulation have been known for a long time. Ancient shamans knew that flickering flames can cause hallucinations. Around 200 A.D. , Ptolemy noted that the flickering of sunlight seen through the spokes of a spinning wheel could cause patterns and colors to appear to the observer, and could produce a feeling of lightheadedness and euphoria. In modern times, (1940's and 50's) neuroscientist W. Gray Walter used a strobe light to create flickering light stimulation, and noted that the brain wave pattern of the whole cortex was changed, not just the area associated with vision. Experimentation in the 1960's and 70's showed that adding pulsing sound enhanced the experience. The invention of the microprocessor made it possible for inexpensive light/sound devices to be produced, and hundreds of thousands of people have tried them. See the references, especially Megabrain by Micheal Hutchison, for more information in this area. Some of the above was extracted from Megabrain.

• Intensity refers to the brightness of the light stimulation.

• Just scale is a seldom used musical scale that has seven notes per octave, and is designed to make chords relative to the base of the octave come out right. The Just scale is used in Photosonix dual binaural beat machines to get better chords, and also because the integer pitches of the Just scale make integer binaural beat offsets work better. (With a pitch ratio of 1.059 you don't get many integer pitches).

• Light frames are eyeglass frames with light sources mounted inside in front of the eyes. The lights flicker on and off during a session at the stimulation frequency. The light source can be colored light-emitting diodes (LED) or incandescent (white) light bulbs. The LED based light frames are designed to be used with the eyes closed -- the eyelids diffuse the light and add to the experience. White light frames have a translucent diffusion mask built in that allows them to be used with eyes open. The circuitry needed to drive white and LED light frames is different, so a "switch" in hardware or software is required if the same system is to drive both types. Beware of systems that claim to do both without a switch. Red LED's can be made brighter than green and provide a more intense experience. Green LED's provide a softer experience and work better for persons who are averse to bright lights.

• Light/Sound Designer is an optional software package for Photosonix downloadable systems. It allows sessions to be designed in a spreadsheet format on a PC computer (under Windows), displayed graphically, stored in a disk format compatible with many popular spreadsheets, and downloaded via a COM (RS232) port to the system. Far and away the best PC software package for Light/Sound program design.

• Light/Sound Librarian is an optional software package for Photosonix downloadable systems. It helps organize sessions, set up downloads of multiple sessions, and print session lists for a downloadable system. Free with any Photosonix session library.

• Mind Machines are devices that influence your state of mind using specially designed light and sound stimulation. We prefer to call them light/sound synthesizers, and do throughout this site. Flickering lights and pulsating sound have been used for centuries to influence moods, from music for relaxation to adrenaline-raising dances around the tribal fire. Light/sound systems have the advantage that the stimulation is more controlled, better designed for its purpose, and you don't have to hire a band. They are very effective relaxation tools, a good assist to meditation, and can aid the learning process.

• Octave is a interval between notes that has a 2/1 frequency ratio (e.g. 220 to 440 Hertz). In the tempered scale there are 12 total notes in an octave, seven "white key" or natural notes and five "black key" sharps and flats. The name octave comes from counting one too many white keys, or maybe because "heptave" just doesn't sound good.

• Phase is the timing relationship between the different stimulation channels --the two eyes and the two ears. When pulsed sounds are selected, there are six phase settings available.

• Pitch refers to the frequency of sound stimulation, and is perceived as "low notes" (bass) to "high notes" (soprano). The Photosonix systems operate in the range of 64 to 960 Hertz. The tones generated by the Pro systems, the Muse^#, the Halcyon and the ProTutor are based on the Just scale, the PLI, 515 and Breathwork Explorer on the Tempered scale.

• Ramping refers to changing a stimulation parameter gradually so that "jumps" are not perceptible. Most light/sound systems can ramp frequency, (but some still "jump" in 1 or 2 Hertz steps -- ask about this before buying). Fewer can ramp volume and intensity, and only Photosonix systems can ramp pitch. Listen to a dual binaural beat session before deciding it's not important to ramp pitch.

• Musical scale refers to the way in which particular sound frequencies are picked as the notes to be used in playing music. An octave is a musical interval with a frequency ratio of 2/1 (e.g. 220 to 440 Hertz). Different cultures and musical traditions have used many different ways of dividing an octave. Western (this is Western as opposed to Eastern, not Country Western) music is mostly based on the tempered scale, with 12 notes per octave and equal frequency ratios between adjacent notes. An interesting variation is the Just scale, used in some Photosonix systems.

• Sessions are programmed sequences of changing light and sound stimulation, designed for a specific purpose such as relaxation, alertness, sleep, etc. Sessions typically last from 15 to 45 minutes, and some systems allow the user to vary the running time. 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. The variety and quality of the built-in sessions on a light/sound system has a profound effect on how well the machine will work for you. The sessions in the Photosonix systems are unique in that musician/composer Chris Oliver has used pitch to enhance the experience.

• 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. On a light/sound system that does not have sine wave sound, the alternative is usually square wave sound (on or off), not because it sounds good (it doesn't) but because it's easy to make on a computer. Mixed tone beats and binaural beats don't work as well on non-sine-wave sound either.

• Soft on/off refers to starting a session by slowly ramping on the sound volume and light intensity, and ending a session by slowly ramping them back off. This feature makes the transition into and out of a session more pleasant, and prevents sudden jerky endings that can destroy the effect of a session.

• Surf is a mixture of lots of pitches -- the synthesized surf sound in Photosonix systems is an approximation to pink noise (equal energy in each octave), cut off at about 1000 Hertz.

• Tempered scale is the musical scale used in modern western music. There are twelve notes per octave with a constant frequency ratio between adjacent notes (the twelfth root of 2, or about 1.059). This approach has advantages in playing music in different keys, but does not make chords come out as well as they could.

• Tone refers to the type of sound stimulation used. The tones used in Photosonix systems are:

  Pulsed tone - sine wave tone at the selected pitch, pulsed at the current frequency, with the selected duty cycle.
  
  Pulsed surf - a surf sound pulsed at the current frequency, with the selected duty cycle.
  
  Alternating tone/surf - the above two tones, alternating in each ear.
  
  Pulsed chord - a chord with controllable base pitch and tone separation, pulsed at the current frequency and duty cycle.
  
  Binaural beats - the ears receive pitches differing by the current frequency.
  
  Binaural beats with tick - binaural beats with a metronome tick at the selected frequency.
  
  Dual binaural beats - each ear receives two pitches, with lots of chord and beat interactions.
  
  Binaural beats with surf - binaural beats with a surf background. This one is unique to Photosonix and really nice.

• Visuals refer to the shifting, colored patterns perceived when you look at the flickering lights on a light sound system. The patterns are optical illusions caused by the interaction of the flicker rate with the sensing and processing rate of your eyes and brain. You may have seen a child's top with radial black lines, that when spun, gives the appearance of changing colors. That is a similar effect. The visual images from a light sound system can be very impressive ("hey, wow, look at this") and contribute a lot to the enjoyment of using the system. A session that creates a good light show is imaginatively said to have "great visuals".

• Volume means what you thought it did -- the loudness of the sound stimulation.