That all said, we are all different and have our own different limits. So I generally advise that you just be aware of how you are feeling, and if you feel like you are getting a bit fatigued from it, it’s probably time to stop or at least take a break. When listening over long extended periods, I recommend that you keep yourself well-hydrated. Your brain needs a good supply of water to function well, especially if you are studying hard and increasing your brainwave electrical activity.

Given that brainwaves control and connect such a vast range of human experience from thought to feelings to actions, it is easy to see how the deliberate control of brainwaves can affect mood, behaviors, motivation, and even physical health. Brainwave entrainment is a safe, simple, and scientifically proven method for quickly guiding the brain into a beneficial brainwave frequency to facilitate healthy sleep, lower stress, heal emotional problems, and improve physical health.

Research: the authors stated that qualitative electroencephalogram signatures needed to be developed for different disorders and tested using standard validated methods of psychological assessment. Larger RCTs were needed with clear inclusion criteria for participants. The RCTs should measure qualitative EEG, hormone levels and the time of day of the intervention. Interventions protocols should be clearly defined and the relationship between session frequency/ duration and outcomes should be explored. More studies of auditory stimulation were needed, as well as studies comparing different types of stimulation, monaural, binaural and isochronic beats and use of white noise versus music.
Beta brainwaves are next highest in frequency after alpha waves, occurring at 13 to 30 hertz. Beta brainwaves are what we experience every day as we are awake and using our analytic mind. Beta brainwaves are needed for concentrating on mental tasks, and when they are present for too long of a time, they lead to stress, anxiety, and even paranoia. Most people do not have trouble achieving beta brainwaves and in fact suffer from spending too much time in beta brainwave patterns. However, those with attention deficit disorder (ADD) who have problems focusing their attention can benefit from learning how to achieve and remain in beta brainwave states for longer amounts of time.
Isochronic tones work by influencing your brainwave activity and they can’t directly affect the body. That said, the brain does control the body, so sensations and feelings can sometimes be felt in the body after stimulating your brainwave activity. Some people who are new listeners of this type of audio can sometimes feel tingling sensations in their body. Not everyone feels this and these sensations usually stop once you get more used to using the audios. Isochronic tones are considered as a safe technology. However, sometimes they can leave you feeling temporarily fatigued, especially if you listen to them for an extended period (hours) when you first start using them. If you felt fatigued, I would recommend using them for a much shorter period while you are getting used to them and ensure you are well-hydrated.

Binaural beats are the playing of two sine waves of close, but not the same, frequency into different earpieces of a set of headphones. The "beat" is heard as the brain tries to process them as a distinct sound, while taking into account the constructive/destructive interference. It is said to migrate brain waves to be closer to that frequency, like a sort of biological resonance, which is true. Of course the same can be said for listening to relaxing music help you relax, up tempo music to help you feel energetic, etc...
Thanks for the coupons, I had originally looked into these cd’s after my doctor recommended them, but my mom wound up buying them for me for Christmas (she didn’t know about the coupons I had!) Anyway just listened to Equisync II today for the first time, I was in such a state as to where I didn’t know if I’d fallen asleep or not! I hadn’t but was in such an amazing place.

Hey, even before we spoke about creating Journey, I was thinking about how people across the world do their spiritual practices and the commonalities between them all. I was thinking, there is the path of stillness—which links right back to what we were talking about getting to a state of deep, profound relaxation and bringing clarity into stillness. Then there’s the path of rhythm, of rocking, of dancing. But there’s always a rhythm to it—even in the movements of Tai Chi, there’s a smoothness, a smooth rhythm. What it never is, is arrhythmic—those are the movements of a more anxious, frightened animal kind of thing. 

Some studies have found that binaural beats can affect cognitive function positively or negatively, depending on the specific frequency that’s generated. For example, a study of long-term memory found that beta-frequency binaural beats improved memory, while theta-frequency binaural beats interfered with memory. This is something for scientists to continue to examine closely. For people who use binaural beats, it’s important to understand that different frequencies will produce different effects.
Newberg won't go so far, but other proponents of the new brain science do. Michael Persinger, a professor of neuroscience at Laurentian University in Sudbury, Ontario, has been conducting experiments that fit a set of magnets to a helmet-like device. Persinger runs what amounts to a weak electromagnetic signal around the skulls of volunteers. Four in five people, he said, report a "mystical experience, the feeling that there is a sentient being or entity standing behind or near" them. Some weep, some feel God has touched them, others become frightened and talk of demons and evil spirits. "That's in the laboratory," said Persinger. "They know they are in the laboratory. Can you imagine what would happen if that happened late at night in a pew or mosque or synagogue?" His research, said Persinger, showed that "religion is a property of the brain, only the brain and has little to do with what's out there." Those who believe the new science disproves the existence of God say they are holding up a mirror to society about the destructive power of religion. They say that religious wars, fanaticism and intolerance spring from dogmatic beliefs that particular gods and faiths are unique, rather than facets of universal brain chemistry.
I have read something different about theta waves and learning languages. A University of Washington study tested students resting brainwave activity before learning French. They found that students with a higher amount beta/gamma and a lower amount of delta/theta activity were better at acquiring a second language. When you are dominant in theta, that is the lowest and most deeply relaxed awakened state you can be in. I think it would be much harder to really concentrate, fully understand and learn new information while in a theta state, so I would personally consider using theta while studying.
... The goal of the study was to observe the effect of exposure to BB on working memory capacity. As suggested by many studies, BBs corresponding to alpha brain waves can positively influence cognitive processing, namely attention, auditory sequential memory, working memory, working memory storage, and reasoning ability (Carter & Russell, 1993;Cruceanu & Rotarescu, 2013;Foster, 1990;Kennerly, 1994;McMurray, 2006). The results show that a BB of the frequency of 9.55 Hz – which is a representation of the alpha frequency range of the brain activity – had a temporary positive effect on working memory capacity in our sample of healthy, adult university students. ...
Beta waves range between 13-40 HZ You are wide-awake, alert. Your mind is sharp, focused. It makes connections quickly, easily, and you're primed to do work that requires your full attention. In the Beta state, neurons fire abundantly, in rapid succession, helping you achieve peak performance. New ideas and solutions to problems flash like lightning into your mind.

Our relaxing music is perfect for Deepak Chopra Meditations, Buddhist meditation, Zen meditation, Mindfulness meditation, Kundalini meditation, Qi Gong Meditation, Zazen Meditation and more. Our music is influenced by Japanese meditation music, Indian meditation music, Tibetan music and Shamanic music. Our instrumental music has been designed to encourage and enhance relaxation, meditation, brain function and concentration, spa and massage therapy, and healing music therapy. In addition, we use binaural beats (Delta, Alpha and Theta Waves) to naturally reach a state of relaxation perfect for concentration, meditation or deep sleep. Our music playlists are perfect for your daily meditation and relaxation. Our music videos use soundscapes such as nature sounds, animals, oceans, rain sounds, thunder sounds and many more).
Entrainment is a phenomenon by which some external sensory stimulation synchronizes brainwaves differently than the native rhythm. The most obvious example of this is photic driving – during an EEG the subject will have a strobe light flashed before them at various frequencies. The purpose of this is to see if it will trigger seizure activity. In many normal subjects the brain wave rhythm in the occipital lobes, which is the visual part of the cortex, will match its frequency to the frequency of the strobe light. This specifically is called photic driving, but the phenomenon in general is called entrainment.
Binaural beats by themselves are dull for some people to listen to. But with nature sounds or ambient music, as well as either white noise, pink noise, brown noise, mixed in with the binaural beats it is more pleasant to listen to longterm. Normally it will take about 6 minutes for the brain to start becoming entrained by the binaural beats. But it is best to listen to binaural beat recordings daily that are any where between 10 minutes to an hour long.

I am fortunate to be working with Deepak Chopra, M.D., and Dr. Rudy Tanzi, co-authors of the bestselling book Super Brain, on a technology called Brain Wave Entrainment. Deepak is very well known, but Rudy is an amazingly interesting person as well. He is the Kennedy Professor of Neurology at Harvard Medical School and Vice-Chair of Neurology at Mass General Hospital. Rudy co-discovered three of the four original Alzheimer's genes and today runs the Alzheimer's Genome Project. He also plays the keyboards, including, at times, for Aerosmith. He is kind of a real life "Buckaroo Banzai."
I was not looking forward to returning back to my house as I live on my own so was very pleased to see that the “equisync” CDs had arrived in my absence. Ever since I have been back I put a CD on each evening and the change has been totally fantastic. The meditation is unbelievably calming and soothing, the inner-voice has been silenced and quite often I just put it on to drop off to sleep with the sound of gently falling rain. I can feel each day starting calmly and things like organising the memorial service have not been the strain and upset I would normally have expected. I could wax lyrical for hours because the benefits are truly and utterly fantastic. Never did I think I would find anything that would lift my spirits, clear my mind, calm the inner space but Equi-Sync has done that, and more.
Entrainment is a phenomenon by which some external sensory stimulation synchronizes brainwaves differently than the native rhythm. The most obvious example of this is photic driving – during an EEG the subject will have a strobe light flashed before them at various frequencies. The purpose of this is to see if it will trigger seizure activity. In many normal subjects the brain wave rhythm in the occipital lobes, which is the visual part of the cortex, will match its frequency to the frequency of the strobe light. This specifically is called photic driving, but the phenomenon in general is called entrainment.
There is also evidence to suggest meditation plays a protective role against the natural reduction in grey matter volume associated with aging. One study found evidence that Zen meditators experienced a slower age related decline rate for cerebral gray matter volume in the putamen which plays a role in learning, cognitive flexibility and attentional processing [14] This could suggest a better attentiveness in aging meditators versus non-meditators.
At the beginning of May, I decided to change over to EquiSync because it’s much cheaper and let me experience the deeper levels sooner. At best, my blood pressure has been down to 66 and after cups of tea and food, back up to 76-80 which is regarded as acceptable. I was able to achieve these wonderful results in less than 6 months of daily practice of meditation using audio-beat technology.
... The goal of the study was to observe the effect of exposure to BB on working memory capacity. As suggested by many studies, BBs corresponding to alpha brain waves can positively influence cognitive processing, namely attention, auditory sequential memory, working memory, working memory storage, and reasoning ability (Carter & Russell, 1993;Cruceanu & Rotarescu, 2013;Foster, 1990;Kennerly, 1994;McMurray, 2006). The results show that a BB of the frequency of 9.55 Hz – which is a representation of the alpha frequency range of the brain activity – had a temporary positive effect on working memory capacity in our sample of healthy, adult university students. ...
Hi Marko, that isn’t one of my videos you referred to, so I can’t really answer you properly as I don’t know how their track was created. For the best answer, you should really contact the video creator. There isn’t any research that I’ve seen to suggest that you could harm your health by looping a delta track. During a typical sleep cycle, your brainwave activity will usually go up and down between the delta and theta range. It may be that you won’t experience the same quality of sleep if you spend most of your time producing mainly delta activity. With my 8-hour sleep track, I fluctuate the frequency range to try and emulate a typical sleep cycle http://www.mindamend.com/shop/sleeping-and-dreaming/deep-sleep-8-hour-sleep-cycle/.
Uses of audio with embedded binaural beats that are mixed with music or various pink or background sound are diverse. They range from relaxation, meditation, stress reduction, pain management, improved sleep quality, decrease in sleep requirements, super learning, enhanced creativity and intuition, remote viewing, telepathy, and out-of-body experience and lucid dreaming. Audio embedded with binaural beats is often combined with various meditation techniques, as well as positive affirmations and visualization.
Slow Wave Sleep or SWS, is the deepest of sleep states and it plays a vital role in health and well being. During this phase of the sleep cycle, the brain begins producing very slow, large Delta waves. Even if your lifestyle doesn’t allow for the luxury of a full eight hours of sleep, a few hours of Slow Wave Sleep will trick your brain into thinking it’s had all the restorative sleep it needs.

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 brain is set up in such a way as to have spiritual experiences and religious experiences," said Andrew Newberg, a Philadelphia scientist who authored the book "Why God Won't Go Away." "Unless there is a fundamental change in the brain, religion and spirituality will be here for a very long time. The brain is predisposed to having those experiences and that is why so many people believe in God."
The main point is, you can be asleep while listening to any of them, but you won't be awake to feel anything. If you fall asleep while a beta binaural beat is playing, you may start to get anxious and start sleeping restlessly, you may even have a bad dream. This is because too much use of the higher beta range is associated with anxiety and stress, it's the “fight or flight” response you will experience.
You can experiment with the length of time you listen to the binaural beats to find out what works for you. For example, if you’re experiencing high levels of anxiety or stress, you may want to listen to the audio for a full hour or longer. Remember, you must use headphones for binaural beats to work. You may also want to listen with your eyes closed.
Controlled or pre/post studies of the effects of BWE using auditory or visual stimulation were eligible for inclusion, provided pulses of light or tone were delivered at frequencies hypothesised to have a beneficial effect or in line with a protocol addressing clinical outcomes. Studies were required to report clinical or psychological outcomes (measured using standard methods or as deemed appropriate by peer review) and to report statistical analysis. Studies of outcomes such as electroencephalogram (EEG) response or neurotransmitter levels were not eligible. Case studies were excluded.
Hi Rona, thanks for your compliments on my videos and the music I use, I’m pleased you’ve found them helpful. Regarding the pulse-like sound you’ve been hearing, I’ve never had anyone report something similar to that before. I also haven’t heard anyone on brainwave entrainment forums mention it. That is very unusual and because I’ve never come across it before, I’m afraid I don’t know what would cause that.
Other entrainment methods sometimes used include autopan modulation that moves sound in an 180º arc to create a desired tone. Harmonic box entrainment, invented by James Mann, uses a layering of binaural and monaural tones that alternate between ears, requiring headphones. Sound modulation and filtering, amplitude modulation, and pitch panning use diverse sounds to create rhythmic pulses matched to the desired brainwave frequency. 
Our Reiki Music and Zen Music is ideal for Reiki healing sessions, and encouraging a state of Zen. Let the calming, subtle sounds take you to a higher state of consciousness, and allow you to give and receive powerful Reiki vibrations. Our Chakra Music use special formulated frequencies for each stage of your chakra. We have individual tracks to unlock your Root Chakra, Sacral Chakra, Solar Plexus Chakra, Heart Chakra, Throat Chakra, Third Eye Chakra and the Crown Chakra. Chakra Music for Chakra Healing, Chakra Balancing, Chakravakem, Chakra Guided Meditations and anything Chakra
^ Jump up to: a b Fox, Kieran C.R.; Nijeboer, Savannah; Dixon, Matthew L.; Floman, James L.; Ellamil, Melissa; Rumak, Samuel P.; Sedlmeier, Peter; Christoff, Kalina (2014). "Is meditation associated with altered brain structure? A systematic review and meta-analysis of morphometric neuroimaging in meditation practitioners". Neuroscience & Biobehavioral Reviews. 43: 48–73. doi:10.1016/j.neubiorev.2014.03.016. PMID 24705269.

John Dupuy is the CEO of iAwake Technologies and travels internationally to teach and inspire on the subjects of Integral Recovery, Integral Transformative Practice, and the use of brainwave entrainment technology to deepen one’s meditation practice and in the treatment of addiction, depression, and PTSD. John is the founder of Integral Recovery® and his book Integral Recovery: A Revolutionary Approach to the Treatment of Alcoholism and Addiction  won the 2013 USA Best Book Award. John also hosts interviews with leading innovators in the spiritual technologies field on Spiritual Technologies 2.0 Live and co-hosts the popular Journey of Integral Recovery podcast.

If you are reading this, it is likely that your Beta brainwaves are dominating your mind. Beta brainwaves are present when your attention is focused on a problem, whether that is working something complex out in your head, Focusing on a video game or having a conversation with another person. Beta waves are also experienced during anxiety, stress and excitement.2
Since opening their online store in 2011, Binaural Beats Meditation has served “hundreds of thousands” of customers, according to James Matthews, the site’s customer happiness manager. “We continue to see an increase in interest… from individuals, but increasingly so from therapists using the music to help clients, health and wellness organizations, and businesses around the world.”

Beta: These brainwaves are associated with high levels of alertness and arousal. When beta brainwave patterns dominate, we’re primed to focus and concentrate, to make decisions and think analytically. When you’re analyzing an issue at work, you’re probably in a beta-dominant state. Beta waves are fast, with a higher frequency (between 15-40 hertz). At the higher levels of this range, beta waves are associated with anxiety.
Brainwave Entrainment has been used possibly as far back as 200AD, where Ptolemy of the Ancient Greeks noted the effect of flicking sunlight created by a spinning wheel. The first recorded clinical application was by a French psychologist, who again used a spinning wheel but this time illuminated with a lantern instead of the sun. He noted that his patients appeared calmer when they looked into the flickering light, so he used it as a relaxation technique whenever it was needed.
Now for the good part: depending on the frequency, binaural beats can be used to manipulate what kinds of waves your brain is sending out to promote sleep, deep thinking, etc. The lowest frequencies, from 0.1-4 Hz, are the best for deep sleep, pain relief, and reduction of stress hormones like cortisol. Additionally, these frequencies aid in the release of DHEA and melatonin, two of the sleep hormones. The next lowest, from 4-8 Hz, promotes REM sleep (when vivid dreaming and memory development occurs), deep relaxation, and is great for meditation. The higher frequencies, from 14 up to 100 Hz, have benefits like increasing focus, awareness and cognitive functioning for activities like information processing and problem-solving.
a concise P.S. I was in a horrible car accident when I was 18 and had to learn to read and write and walk and talk all over again. It was long ago and I’m pretty well over it, but such an injury has lifetime repercussions. The neurological damage sustained causes my left arm to shake uncontrollably anytime I use it in a situation requiring precise coordination. From simply listening to the demo, the shake [though not disappearing completely in the last 2 months] has lessened dramatically. I had been wondering for years what kind of neurological exercises I could undergo to help it…

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.


Brainwave entrainment through the use of binaural beats is a scientific method that helps you go from alert to relaxed to asleep within minutes by using a process to alter your brainwaves. Sounds like something straight out of a science fiction novel, but brainwave entrainment is a very real and very effective way to help you sleep. Your alertness is linked to the dominant frequency of your brainwaves. So if you’re feeling alert and focused, your brainwaves are in the beta frequency but if you’re feeling relaxed, they’re likely to be in the alpha state. To sleep, your brainwave frequency needs drop to a slow delta. This can be hard, especially after a busy day. Your brain stays alert, preventing you from relaxing. By using Binaural Beats, you can quickly induce the frequencies associated with sleep in your brain within minutes.  Scientists discovered that the brain synchronises itself to a dominant frequency. So by inducing a new lower frequency with binaural beats, your brain begins to lower its own frequency to match this new frequency. It’s a powerful technology that I’ve been using myself for years with very good results.
A good recording will also not immediately start with tones that produce the theta range, but will begin higher up, in the beta range (which is associated with anxiety, but also active concentration and other waking states of being), and gradually move down, through the alpha range (which is the ideal meditative wavelength, but is also associated with falling asleep) before moving into the final, theta, range. If you get a binaural beat that goes directly into the theta range, you might find yourself distracted or unable to sync up as easily.
I have read something different about theta waves and learning languages. A University of Washington study tested students resting brainwave activity before learning French. They found that students with a higher amount beta/gamma and a lower amount of delta/theta activity were better at acquiring a second language. When you are dominant in theta, that is the lowest and most deeply relaxed awakened state you can be in. I think it would be much harder to really concentrate, fully understand and learn new information while in a theta state, so I would personally consider using theta while studying.
In one study, researchers had a group of participants relax alone in a quiet, low-light environment following an exercise session. They split the group in two — one spent 20 minutes listening to theta-frequency binaural beats while the other listened to a carrier tone and monitored their parasympathetic (rest and relaxation) and sympathetic (fight or flight) nervous system activity. Researchers found the group that listened to binaural beats experienced an increase in parasympathetic activity and a decrease in sympathetic activity, along with higher rates of self-reported relaxation.

Well, I finally listened to “Equisync III” after listening to “Equisync I” & the “Equisync II” several times. Let me just say that this put me in another state of consciousness within 7 minutes(guessing) it was beautiful! I meditated throughout the entire 70 minute CD set! It didn’t feel like 70 minutes. I could feel energy in my neck, my solar plexus area and at the brow of my head! Definitely NOT for beginners!
“…humans have always been intrigued by the possibilities for influencing mental functioning that emerge from combining rhythmic sound and rhythmic light stimulation. Ancient rituals for entering trance states often involved both rhythmic sounds in the form of drum beats, clapping, or chanting and flickering lights produced by candles, torches, bonfires, or long lines of human bodies passing before the fire and chopping the light into mesmerizing rhythmic flashes. From Greek plays to Western opera, our most popular entertainment forms have made use of combinations of lights and sounds. Some composers, such as the visionary Scriabin, actually created music intended to be experienced in combination with rhythmic light displays.”
All brainwave frequencies are useful and beneficial at certain times – there is no brainwave that is intrinsically better than another. However, by deliberately choosing to attain a particular brainwave state, a corresponding mental state can be brought about at the same time. For example, a working person who has been in an overly alert beta brainwave pattern for many hours can quickly shift their mind and body into a relaxed state by listening to a few minutes of brainwave entrainment music for inducing alpha or theta brainwaves.
Scientists and clinicians use brainwaves to measure and understand the functioning of the brain. We typically can’t see them, but human brains have billions of neurons. These individual neurons connect to thousands of other neurons. And when brain activity happens, these neurons light up much the same way thousands of audience members do “the wave” in an arena.
Meanwhile, the therapeutic benefits of listening to sound and music is a well-established principle upon which the practice of receptive music therapy is founded. The term 'receptive music therapy' denotes a process by which patients or participants listen to music with specific intent to therapeutically benefit; and is a term used by therapists to distinguish it from 'active music therapy' by which patients or participants engage in producing vocal or instrumental music.[37] Receptive music therapy is an effective adjunctive intervention suitable for treating a range of physical and mental conditions.[38]
Given that brainwaves control and connect such a vast range of human experience from thought to feelings to actions, it is easy to see how the deliberate control of brainwaves can affect mood, behaviors, motivation, and even physical health. Brainwave entrainment is a safe, simple, and scientifically proven method for quickly guiding the brain into a beneficial brainwave frequency to facilitate healthy sleep, lower stress, heal emotional problems, and improve physical health.
Since most of us spend our days in the beta state, EquiSync excludes the beta brainwave frequencies, and entrains only those responsible for the most beneficial brainwave states: alpha, theta, and delta waves. The two charts on this page illustrate the basic benefits of each brainwave state as well as the basic targeting of the EquiSync programs 1, 2, & 3.

Long-term meditation practitioners have also shown to have a higher tolerance for pain.[15] This effect has been correlated to altered function and structure in somatosensory cortices and an increased ability to decouple regions in the brain associated with the cognitive appraisal of pain (anterior cingulate cortex and dorsolateral prefrontal cortex).[16]
While the physiological and psychological processes being uncovered by brain science in the study of brainwaves is sometimes complex and still being investigated, certain basic principles are well-established, easily understood, and helpful for achieving the most effectively use of brainwave entrainment when seeking relaxation, improved sleep, lowering of anxiety, or other goals. This important background information and scientific knowledge presented here includes: 
So to summarize their claim, they're saying that entrainment means that a binaural beat will cause your brain's electroencephalogram to match the pattern of the phantom beat. Well, if it did, entrainment certainly doesn't apply and would not be part of the equation, so we can scratch that off the list. But it doesn't make the claimed observation wrong. We do know that certain electroencephalogram waveforms are often associated with certain kinds of activity. For example, physical activity or REM sleep often produces an electroencephalogram with a sine wave of between 4 and 8 Hz, which we term a theta pattern. Waking relaxation with eyes closed often produces a pattern from 8 to 12 Hz, which is called an alpha pattern. There are only a few characterized patterns, and pretty general descriptions of what kinds of activities go with them. The claim made by the binaural beat sellers depends on much more granular and specific matches. For example, the claim that a binaural beat with a frequency of X produces the same effect in your brain as Vicodin is wholly implausible. Such claims presume that we know the exact frequency of the electroencephalogram in each of these desired conditions, and the fact is that brain waves don't work that way. It is wholly and absolutely implausible to say that desired brain condition X will occur if we get your EEG to read exactly X Hz.
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