With digital upgrades, Berger’s machine is still in use today, known as an electroencephalography machine, or EEG. Berger used his machine to study the brains of psychologically normal and abnormal people and discovered the first brainwave, called the alpha wave and also known as the Berger wave, along with the faster beta wave, which he observed suppressing the alpha wave when subjects opened their closed eyes. 
A therapy that slows brainwave activity, helping to produce low-frequency waves, is likely to aid relaxation and sleep. But it’s not only lowering brainwave frequency that binaural beats may offer to sleep and relaxation. A small study (19 people) has found that exposure to binaural beats is associated with changes to three hormones important to sleep and well being:
You’ve heard the “om” sound yogis make when they meditate, right? Well, Joshi says using a buzzing sound is another way to use your voice to calm yourself in the midst of a freakout. “Bhramari, a humming bee sound, can be done by closing the eyes and making the humming sound like a bee,” she says. “These sound vibrations calm down the thought waves and relax the entire nervous system. External sound frequency resonates with the internal rhythm of the body and mind, creating peace and tranquility within.” Research from India has shown Bhramari to improve cardiovascular patterns. Press your ears closed for an even stronger vibration.
When explaining this to others they frequently respond with something like, “But I had no expectation or even any idea that my face might experience flushing. I didn’t even know that was possible. Now every time I listen to a particular entrainment track that specific face flushing occurs. If it is a specific phenomena, and it only happens when I use one certain entrainment track, doesn’t that prove it is the entrainment causing it?”
Most programs start at a work/life busy brain Beta frequency of twenty light flashes per second (20Hz) and slowly ramp them down to Alpha (relaxation and meditation) at 8-12 HZ, Theta (deep relaxation and dreaming) at 4-8 Hz) and Delta (dreamless deep relaxation) of .5-4Hz. We have taken measurements at Mass General with state of the art EEG equipment and have seen a slowing of the brain waves from Beta to Theta in two minutes and complete brain wave harmonization in the left, right, anterior, posterior and occipital regions of the brain.
Yoga has been shown to have similar benefits, reinforcing the “mind-body connection,” improving how people (especially women) feel about their bodies, helping with sleep and controlling anxiety. A review of over 35 clinical trials that tested the effects of regular yoga on stress levels and health found that, overall, yoga offers significant improvements in various physical and psychological health markers for the majority of people. (3)

There’s also some new stuff I’ve certainly never included in tracks before including some gentle pink noise and brown noise blended together in the background with what’s called phase modulation. This is almost outside of awareness as you’re listening to it. This is how your ear tells what direction a sound is coming from. Does it arrive at your left ear slightly before your right ear? You can modulate that. So, again, it has a very gentle, imperceptible rhythmic quality to it.
The effects are strongest while you are listening to the tones because your brainwaves are synchronized and tuned into the frequency range you desire at that time.  After you've stopped listening the effects can still linger for a while afterwards.  The timescale will vary from person to person and be affected by what you do after you've stopped listening.
The most common way to use a brainwave entrainment is for a short-term benefit, to help guide your brain into a particular mental state at the time you need it.  In a similar way to how you might take a sleeping pill before bed to help you get to sleep, or maybe drink some coffee or an energy drink to help wake you up and give you a boost of energy.

Delta brainwaves have the slowest frequencies, ranging between 0.1 and 4 hertz, and these are the brainwave states associated with deep sleep, trance states, and unconsciousness. Few people can remain awake during delta brainwaves states, although this state is recorded in awake infants between ages of three months and one year and also in babies just before birth. Delta waves are also linked with increased production of HGH, DHEA, and the neuro-transmitter serotonin.
It’s important to keep in mind; a person’s own experiences will be somewhat relative to their starting point. If you are a person who is completely stressed out, burned out, hanging on the ragged edge, experiencing total adrenal fatigue, and you’ve been at that point for awhile, then to you even a small degree of mental quiet and physical relaxation that meditation and brainwave entrainment bring will feel like a tsunami of relief.
When two pure tones of slightly different frequencies are delivered simultaneously to the two ears, is generated a beat whose frequency corresponds to the frequency difference between them. That beat is known as acoustic beat. If these two tones are presented one to each ear, they still produce the sensation of the same beat, although no physical combination of the tones occurs outside the... [Show full abstract]
Science shows that massages reduce stress, but you don’t have to go to the spa—you can give yourself one right now. “Learning how to self-massage your foot, head, neck, or shoulders reduces the stress hormone cortisol, boosts your immune system, and increases the feel-good hormones oxytocin, dopamine, and serotonin,” Dr. Serani says. You can even use a tennis ball or cold water bottle on your feet or neck. In addition, try rubbing pressure points like the webbing between your thumb and index finger, or your inner wrist. Another technique is the EFT tapping technique, literally tapping certain points on your body such as in between your eyes, your temples, and the center of your collarbone. “Tapping brings cleansing energy to the meridian points, as your mind directs the energy to what’s unbalanced in the body,” Whitaker says. “This restores your mind and body’s natural balance, which aids in releasing stress, worry, fears, and disharmony.”

Looking for an even more impactful way to feel the benefits of exercise? Do so while listening to uplifting music. Research findings indicate that music listening positively impacts the psycho-biological stress system, helps activate the parasympathetic nervous system, improves recovery time, and has benefits for hormonal balance and brain functioning overall. (4)
The mechanism for this is that when your eyes or ears are exposed to a particular frequency of pulses or beats, the thalamus first distributes this information to the entire brain, including the visual and cerebral cortex where neural activity begins to synchronize to the incoming frequency, producing hemispheric synchronization and a balance of brainwave activity across the brain.
Binaural beats were discovered in 1839 by a German experimenter, H. W. Dove. The human ability to "hear" binaural beats appears to be the result of evolutionary adaptation. Many evolved species can detect binaural beats because of their brain structure. The frequencies at which binaural beats can be detected change depending upon the size of the species' cranium. In the human, binaural beats can be detected when carrier waves are below approximately 1000 Hz (Oster, 1973). Below 1000 Hz the wave length of the signal is longer than the diameter of the human skull. Thus, signals below 1000 Hz curve around the skull by diffraction. The same effect can be observed with radio wave propagation. Lower-frequency (longer wave length) radio waves (such as AM radio) travel around the earth over and in between mountains and structures. Higher-frequency (shorter wave length) radio waves (such as FM radio, TV, and microwaves) travel in a straight line and can't curve around the earth. Mountains and structures block these high-frequency signals. Because frequencies below 1000 Hz curve around the skull, incoming signals below 1000 Hz are heard by both ears. But due to the distance between the ears, the brain "hears" the inputs from the ears as out of phase with each other. As the sound wave passes around the skull, each ear gets a different portion of the wave. It is this waveform phase difference that allows for accurate location of sounds below 1000 Hz(9). Audio direction finding at higher frequencies is less accurate than it is for frequencies below 1000 Hz. At 8000 Hz the pinna (external ear) becomes effective as an aid to localization. In summary it's the ability of the brain to detect a waveform phase difference is what enables it to perceive binaural beats.
The advice “take a deep breath” may seem like a cliché, but it holds true when it comes to stress. For centuries, Buddhist monks have been conscious of deliberate breathing during meditation. For an easy three- to five-minute exercise, sit up in your chair with your feet flat on the floor and hands on top of your knees. Breathe in and out slowly and deeply, concentrating on your lungs as they expand fully in your chest. While shallow breathing causes stress, deep breathing oxygenates your blood, helps center your body, and clears your mind.
Regarding split hemisphere isochronic tones. Think of this as two separate isochronic tones tracks playing independently of each other, one playing in one ear and the other one in the opposite ear. Better still, imagine someone playing and recording a drum beat at a rate of 5 taps per second (5Hz – 5 cycles per second). Then a separate recording of a drum beat is made at a rate of 10 taps per second (10 Hz). You then make an audio track where the left ear/channel hears the 5 drum beats recording and the right ear/channel hears the 10 beat recording. With headphones on, each ear can only hear each respective drum beat and not the other. So you are hearing two different beat recordings at the same time, but it’s different in each ear. A split hemisphere isochronic tones track works just the same. You hear two beats at the same time, not two tones as with binaural beats that create a single beat, but two different speeds of beats in each ear. This is what enables you to stimulate and influence each side of the brain with a different frequency of beat. Binaural beats can only stimulate and influence a whole brain effect using a single beat.

... [9] While entrainment by binaural auditory beats in the alpha frequency has also been shown to enhance creativity, cognition, memory, and an improvement in intelligence tests and achievement tests in learning disabled boys. [10][11][12][13] The gamma-band activity has been shown to involve in a variety of functions such as attention, memory, and consciousness. Current literature suggests that entrainment by gamma beats promotes cognitive flexibility, modulates visual attention, and enhances creativity. ...
When tuning instruments that can produce sustained tones, beats can be readily recognized. Tuning two tones to a unison will present a peculiar effect: when the two tones are close in pitch but not identical, the difference in frequency generates the beating. The volume varies like in a tremolo as the sounds alternately interfere constructively and destructively. As the two tones gradually approach unison, the beating slows down and may become so slow as to be imperceptible. As the two tones get further apart, their beat frequency starts to approach the range of human pitch perception[1], the beating starts to sound like a note, and a combination tone is produced. This combination tone can also be referred to as a missing fundamental, as the beat frequency of any two tones is equivalent to the frequency of their implied fundamental frequency.
You are already far beyond the need for using an entrainment product as a meditation aid. Those who sincerely believe this to be the case would not have come searching for a meditation site such as Project Meditation to help them learn and practice meditation and brainwave entrainment. They would probably not even bother with using an entrainment aid; hence this entire discussion would be irrelevant to them. The fact that you are here, reading this, seeking to benefit from incorporating meditation and brainwave entrainment to aid in your existing meditation practice suggests you are not one of these folks whose development is so advanced that entrainment is of no use to you.
With almost 100 years of research validating the effectiveness of brainwave entrainment, it’s no wonder why it’s used by thousands of people all over the world. What does the future entail in this exciting field? With the adoption of smartphones, virtual and augmented reality, and advancements in technology reducing the cost of EEG and other forms of biofeedback devices, the entrainment possibilities are endless.
Brainwaves, or neural oscillations, share the fundamental constituents with acoustic and optical waves, including frequency, amplitude and periodicity. Consequently, Huygens' discovery precipitated inquiry[citation needed] into whether or not the synchronous electrical activity of cortical neural ensembles might not only alter in response to external acoustic or optical stimuli but also entrain or synchronize their frequency to that of a specific stimulus.[16][17][18][19]
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