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 may be that you had the volume too loud, but I would expect you to hear the effects of that straight after you’ve stopped listening, not on a day you haven’t used them. It might be something similar to muscle memory, where you suddenly remembered the sound and sensations it gives you as if you were hearing it again. I don’t know how long you’ve been using this type of thing for, but maybe it’s something that will settle down and disappear once you become more accustomed to the sound.

The implications and potential benefits of brainwave entrainment technology are staggering, and a seemingly infinite amount of doors have been opened to be explored.  This technology is highly useful in the self-help/personal development field in a variety of ways.  It can also be used to enhance NLP and hypnosis recordings to make the mind more receptive to suggestion.  Brainwave entrainment can be applied to help people fall asleep, to improve focus and concentration, or to relax.  Recent and modern experiments are also being held to see if brainwave entrainment may help  to treat and/or cure mental “disorders” such as depression or ADD.  One of the most common and popular uses of brainwave entrainment is to effortlessly induce deep meditative states.
Today, EEG machines are used for diagnosing epilepsy and sleep disorders, for determining dosages for anesthesia, and measuring the brain activity of people in comas or suffering from brain trauma. EEG machines also continue to play a role in researching and understanding brainwave entrainment and developing new and better methods for delivering the benefits of this form of brainwave modification. 
In simplest form, they are an audio technology which are used for (safe) brainwave entrainment. Our subconscious mind operates, throughout the day and night, in various brainwave state frequencies, measured in cycles per second (Hz) These frequencies range from the slowest (Delta) frequencies experienced in deep, dreamless sleep and in deep meditation where your conscious-awareness is fully detached, to the fastest (Gamma) frequencies associated to stimulating flow states, high-level thinking and information processing. There are actually 5 known brainwave state frequencies each having their own set of unique characteristics:
First discovered by biophysicist Gerald Oster at Mount Sinai Hospital in New York City, Brainwave Therapy sends pure, precisely tuned sound waves of different frequencies to your brain via stereo headphones. In his EEG research, Oster discovered that when different vibrations, or sound frequencies, are delivered to the brain separately through each ear (as with stereo headphones), the two hemispheres of the brain function together to "hear" not the external sound signals, but a third phantom signal. This signal is called a binaural beat, and it pulses at the exact mathematical difference between the two actual tones. For example, a signal of 100 Hz delivered to the left ear, and a signal of 107 Hz delivered to the right creates a binaural beat of 7 Hz that in this case falls into the Alpha range
This music encourages a state of alpha relaxation. The alpha state is a pleasant state of relaxed alertness. It’s a state that many people experience when they are waking up in the morning or when they are just beginning to drift off to sleep at night. While in a state of alpha relaxation, the mind is quite clear and receptive to information, learning is accelerated and one’s sense of creativity is enhanced. The mind is also very open to positive suggestions during this state.
Insomnia: Perhaps one of the most promising uses of brainwave entrainment technology is for those struggling with insomnia. While the technology is unlikely to provide a “cure” it may help those who have a high level of arousal or are “keyed-up” – reduce their level of internal arousal and sleep. Specifically insomnia that is induced by excess stress (e.g. beta activity) would likely benefit from slower wave stimulation (e.g. alpha activity) to aid the brain in transitioning into sleep.
Because the brain filters and interprets reality in a split-brained way, we tend to see things as separate and opposed, rather than as connected and part of the oneness spoken of by the great spiritual teachers (and, in the last few decades, by quantum mechanical physicists). Thus, at a deep level, the dual structure of our brain, in conjunction with brain lateralization, predisposes us to see and experience ourselves as separate from, and often in opposition to, the rest of the world—instead of experiencing the elegant interconnectedness between us and everything else. Our childhood associations and programming build on this inborn tendency by training us to seek this and avoid that, to move toward pleasure and away from pain, to do good and not bad, and so on. The greater the lateralization in the brain, the greater the feelings of separation—and the greater the feelings of separation, the greater the fear, stress, anxiety, and isolation.
A crossover RCT of a single session of theta stimulation in four healthy adults reported no significant improvement in verbal fluency or attention associated with the intervention and a reduction in immediate recall. Controlled comparisons reported significant benefit from the intervention in all three outcomes measured. Six pre/post studies reported significant benefit from the intervention for 19 of 28 cognitive outcomes.
Brain Wave Entrainment is any procedure that causes one's brainwave frequencies to synchronize with a periodic stimulus (sound, vibration or light) having a frequency corresponding to the intended brain-state (for example, to induce a trance, dreams, sleep or relaxation.) It is also called the Flicker-response because of how staring at a campfire or the flickering of a burning candle can lull you into a state of calmness and serenity. There was an extensive article on this phenomenon by Gerard Oster in Scientific American in 1973. It may sound novel, but in many ways, this is old tech.
Brainwave Mind Voyages 24 CD Set: Brainwave Meditation Programs, Hemispheric Synchronization, and Brainwave Entrainment Technology (24 BMV CDs: Lucid Dreaming, Astral Trance, Alpha Brainwaves, Theta Brainwaves, Delta Brainwaves, Tones, Astral Vibrations, Remote Viewing, Beta Brainwaves, Lucid Dream Cycle, Lucid Dreams Hypnosis, Guided Dream Incubation, The Whales CD, Rainstorm, The Waters CD, Nature Sounds, Heartbeat Meditation CD, The Om Meditation, Ganzfeld Effect/ White Noise, Breathing Silent Mindfulness, Breathwork Yoga Yogic Breathing Techniques, Tibetan Singing Bowls, Schumann Resonance, Sacred Healing Frequencies Solfeggio Healing Tones)
Isochronic tones are basically just a single tone with the volume being turned on and off at regular intervals. When you apply the same effects to music or a noise, it’s usually referred to as amplitude entrainment effects (in Mind Workstation anyway). When you apply the on/off effect to music or noise it’s usually done by targeting a specific frequency range in the sound and only turning that part on/off, leaving the rest of the music/noise untouched. What that does is allow parts of the music/noise to play without being distorted/interrupted, making it sound more pleasant to listen to. It produces a kind of fluttering sound as I like to call it and you can adjust the level of intensity.
Chronic fatigue: Subjective improvements in energy level may be reported by those who increase stimulatory beta and gamma waves. Fast waves tend to be associated with higher levels of arousal. Low arousal is associated with chronic fatigue and may be exacerbated by slow brain waves (e.g. theta and delta). As of now there aren’t any studies that have analyzed various protocols for their effect on a person’s energy or arousal.
Brainwave Entrainment is the process of synchronizing the brain to specific frequencies and patterns embedded in audio tracks. These frequencies correlate to specific emotions, feelings, and even energy levels. Using nothing more than sound, Brainwave Entrainment can enhance creativity, change moods, and even alter behavior like sleep and energy levels.

Theta waves have another interesting characteristic. The Earth has a measurable resonance of 7.83 hertz known as the Schumann resonance. Because the Schumann resonance is a constant background frequency surrounding all life, it may play a special role in biological activity. The Schumann resonance frequency falls within the range of theta brainwaves and may have something to do with why these brainwave frequencies are so powerful. 
Thanks for your appreciation of what I’m doing. I’ve been asked for help with autism a number of times over the years, so it’s something that I’ve often looked into and tried to find new information about. Unfortunately, I’ve yet to find any specific research relating to it and using the type of brainwave entrainment tones I use. There are a number of opinions and claims out here, but I’ve often found them to be conflicting. While some are recommending higher frequency gamma waves, others are recommending lower frequency alpha and theta waves while meditating.
Robert Monroe, a radio producer and executive published a popular book called Journeys Out of the Body about his out-of-body experiences when using brainwave entrainment. He later founded an original brainwave entrainment audio company, Hemi Sync. In 1981, the book Mega Brain by Michael Hutchison brought brainwave entrainment information, techniques, and terminology into the popular press.

I like it. I like the fact that I can just sit there and observe my thoughts and feelings and then go back to watching my breathing. It really does teach me to be centered and balanced. I look forward to the next several weeks. By the way, what I am doing now is meditating for 23 minutes in the early morning and again 23 minutes in the early evening. I’ll check back with you.
Monaural beats have similarities to binaural beats, but the two separate frequencies are delivered through a pulse pattern and mixed before they reach the listeners ears, resulting in the advantage of being audible without stereo headphones. However, using stereo headphones intensifies the effectiveness of monaural beats and is recommended for the best effect. 
So let’s start with the basics, and we can move on from there. An easier way to understand brainwave entrainment would be to think about how your brain gets entrained in real life, without the use of any technology. Have you ever heard a song on the radio that stuck into your mind throughout the day and maybe even the next one? Now think about a repeating sound, like the ticking of a clock – simply listening to it your brain starts producing alpha waves that match that tick-tack sound. Or have you ever been at a meeting when you immediately felt sleepy? That is because the majority of people in the room were feeling that same way and your brain simply matched the brain wave patterns they have been emanating. We can go on exemplifying this phenomenon, but the main point is that our brain is altering and adapting in direct response to what we hear, think, and see.

Deep relaxation is another major benefit resulting from the brains cortical frequency following response while using brainwave entrainment. As the brain tends to mimic the rate of frequency it is exposed to, thus allowing it to enter into that brainwave state, this helps explain why this technology can produce benefits commonly found with meditation.
A few months ago I decided to test the ability of the “Equisync II” brainwaves therapy combined with other more traditional self-improvement programs and the results have been even more amazing to me. Currently in my mind I honestly believe this type of therapy can be a breakthrough, or simply the genesis of a new type of therapeutic techniques to correct several psychological, and behavioral human issues including depression, lack of organization, and self-esteem among many, many other possibilities.

Kelly Howell brings 30 year's experience to her expertise. She has been cited by the Mayo Clinic as "renown for her pioneering work in healing and mind expansion (and) visionary recording techniques." She has collaborated with neuroscientists and biofeedback therapists to invent a sophisticated sound recording technique that makes Brain Sync programs more effective. The result is the most elegant and effective brainwave synchronization audio programs available in the world today. You'll feel the effects from the very first time you listen. With regular use, you'll establish new healthy patterns that last. Brain Sync programs use window frequencies – extremely precise frequencies that fit through narrow biological windows to impact the body at the cellular level. The choice of frequencies selected for each program is based on biofeedback research. Programs are designed to help you self-generate optimized brain states exhibited by remarkable men and women.
I just wanted to thank you guys for having such an outstanding product available. I used to meditate when I was younger but got away from it over the last 7-8 years. I had difficulty starting back up, but since I started using your cds I have no difficulties getting back into it; and am now meditating 2 hours per day and have never felt better. I have only been using them for a couple weeks but have already noticed a difference. Thanks again for creating such a wonderful product and I will be sure to recommend it to everyone.
The only thing I have found lacking in using your product is that there is no place on your website to register my kudos to you for such an excellent product. I am not new to meditation, nor to brain entrainment products, and I found you product to be really outstanding. I’m completely hooked, love listening to the tracks and they are the best way ever to treat monkey mind. Bada boom, bada bing, in just a few minutes any aggravation I’m experiencing in the outside world, melts away and I am one very blissful and happy camper.
Brainwave entrainment represents a way of using technology to take our meditation and our spiritual practices into territory that has previously been very difficult, if not impossible, for us to venture into. My inspiration for creating the Profound Meditation Program 3.0 was not about just adding binaural beats or isochronic tones to music, using conventional audio entrainment methods to create brainwave patterns, and say, “Hey, this is the next big thing!” To me, it is all about what we can do—even if it’s pulling from way outside of the box—to enable such a profound coherence that we can go to meditative depths that have been practically out of reach. With the Profound Meditation Program 3.0, I wanted to do something that hadn’t been done before, taking the technology to the next level.
Another general benefit of using brainwave entrainment in general is that it increases and promotes whole-brain functioning, meaning that the two hemispheres of the brain grow more connections and exchange information more easily. This can help more starkly rational people become more intuitive, and more airy-fairy people become more focused and logical.
Business executive and radio producer Robert Monroe started experimenting with brainwave entrainment and has a series of powerful out of body experiences using it. In 1971 he published his cult classic “Journeys Out of the Body” sharing his experiences. He later created one of the first audio entrainment companies called Hemi Sync, alongside the Monroe Institute of Applied Sciences.
Brainwave entrainment is clearly NOT an effective standalone treatment for mental illness, but it may be an effective adjunct treatment in certain individuals. It should also be mentioned that when using brainwave entrainment, you may want to have a specific purpose in mind. If your goal is to relax, yet you’re using a protocol that is stimulating, you may falsely conclude that it doesn’t work even though you’re using the wrong protocol.

Hi Julie! You’re very welcome for the info. In answer to your question, I think some are probably good, and some not so good. There are many people putting brainwave entrainment out there these days and it is not so easy to figure out which ones are and aren’t of reliable quality without investing time and doing some research. I would say (in general) that paid products are probably better quality than free ones, but I couldn’t guarantee this is a golden rule. My best advice is to just do your research before spending too much time listening to the freebies.
There are many advantages and disadvantages with binaural beats. One of the major advantages is hemispheric synchronization. Since both hemispheres are required to create the beat within the brain, this method is an excellent way to create greater harmony between areas of the mind typically functioning independently. Binaural beats are also known to have effective hypnotic and relaxing effects.
To get a full answer you should really get in touch with the owner of the app, because it does really depend on how their track is constructed and how they intend it to work. I have one 50-minute sleep track which takes you down into delta (http://www.mindamend.com/shop/sleeping-and-dreaming/sleep-induction-isochronic-tones/) and that is designed to just get you to sleep, so you just let play until the end. If you played that track on repeat it might make you jump and wake you up, as the track begins at a higher frequency. I have another 8-hour sleep track which is meant to be played all throughout the night (http://www.mindamend.com/shop/sleeping-and-dreaming/deep-sleep-8-hour-sleep-cycle/). So it does depend on the individual track you are using.
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