Hi Jason, thanks for all the uploads to youtube. I’ve been using them in work recently to help me concentrate and relax. I like the music tracks that you’ve chosen to overlay the tones. A couple of times in the last 2 weeks I’ve experienced the wavy pulse like sound, similar to the tones in my left ear. I wasn’t listening to tracks at the time or that day. It doesn’t last but it feels a bit strange. I wondered if I might have been listening to the tracks too loudly and that it was almost like a type of tinnitus. I’m curious to know if anyone has been in touch with you in the past to say they’ve had a similar experience?

Brainwave entrainment is a colloquialism for such 'neural entrainment', which is a term used to denote the way in which the aggregate frequency of oscillations produced by the synchronous electrical activity in ensembles of cortical neurons can adjust to synchronize with the periodic vibration of an external stimuli, such as a sustained acoustic frequency perceived as pitch, a regularly repeating pattern of intermittent sounds, perceived as rhythm, or of a regularly rhythmically intermittent flashing light.


In the meta-analysis performed by Fox et al., several sources of bias were indicated which bring into question the validity of meditation studies which use neuroimaging. Fox et al. suggests a publication bias may be leading to the over-reporting of significant results.[18] Despite this, however, Fox et al. found "consistent differences in prefrontal cortex and body awareness regions" in "areas key to meta-awareness..., exteroceptive and interoceptive body awareness..., memory consolidation and reconsolidation..., self and emotion regulation..., and intra- and interhemispheric communication..." and that changes were significant with "moderate" global median effect size and "consistent and medium-sized brain structure differences."[18]
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:
Listening to binaural beats is not something to be feared, however. In most situations, listening is safe and very enjoyable. Choosing a track from various websites online, as well as some videos on YouTube.com, can assist you in relaxing and can bring about a more restful sleep. Choosing a Beta entrainment can help with alertness and focus, while listening to an Alpha wave track can help you to relax and learn new information. Theta tracks can help to change some negative emotions, or to help you drift off to a sounder sleep. Delta waves will help to accelerate healing. To use them, you must use headphones or earphones, because each ear will hear a different frequency. You should make the commitment and listen daily; consistency is key in order to achieve maximum benefits. However, please don't listen to binaural beats twenty four hours a day; once daily for a short period of time is perfectly fine. You should also make yourself comfortable; either lying down or sitting in a comfortable chair will help you to relax. You can do them right before sleep, or right upon awakening. Listening during meditation or visualization exercises will help to improve and deepen your practice. If you feel a little blue or you need a break from the daily routine, you can pop a CD in and unplug completely. When you return to whatever you were doing, you will find that you are more refreshed and ready to take on whatever is before you.
So, in summary, binaural beats certainly do not work the way the sellers claim, but there's no reason to think they're any less effective than any other music track you might listen to that effects you in a way you like. If they make you sleepy (like they all do for me), use them to go to sleep. If they relax you or get you amped, use them for that. But don't expect them to be any more effective than regular music. If someone you know claims that they are, put them to the test, and bust the myth.
This incredible app which you  not only has over 3 hours of meditations valued at $200, the technology utilized is unlike anything else on the marketplace. The heartbeat synchronization augmentation gives you a completely immersive experiencing, tuning in to your body’s natural rhythms. It gives you the best binaural music on the market. Fully customizable, you can base your meditation on your mood, goals and timeframe. This is the perfect app for a deep, introspective experience.

People with a past history of epilepsy or seizures should NOT use brainwave entrainment. Those with heart disorders or taking mood-altering pharmaceutical drugs should consult a doctor before trying. Also, some of the frequencies within the videos may make you feel sleepy. As a good practice, please do not listen whilst you are operating machinery or vehicles or carrying out any responsible duties.
When I am using equisync I feel kind of like it is “pushing me” – I guess this is the right way to say it- to achieve better results, which I really like. I fall asleep quickly, and sleep all night and even wake up before my alarm goes off. I feel noticeably calm during the workday- which is very helpful for what I do. I really like the warm feeling (my whole body gets really warm during my equisync meditation sessions) and I feel kind of like Im floating while listening. The soothing rainfall is also very nice.
Cvetkovic D, Simpson D, Cosic I (2006). “Influence of sinusoidally modulated visual stimuli at extremely low frequency range on the human EEG activity“. Conference proceedings : … Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 1: 1311 – 4. doi:10.1109
Your brainwave activity during sleep is largely distinct from your brain activity when you’re awake. (REM sleep is one exception to this—during REM, your brain is active in ways very much like when you’re awake.) During non-REM sleep, the slower, lower frequency theta and delta waves dominate, compared to the alpha and beta waves that are prominent when you’re alert and active.

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.
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/.

With regard to listening without headphones specifically, you might find it irritating if you are someone who suffers from motion sickness, depending on how the track is created. If you were listening to binaural beats, they really need headphones to work properly. If you are in a room and closer to one speaker you may not even hear binaural beats properly, and if sitting off centre in the room generally, that may have unsettled you if you have motion sickness as the tones try to form a beat in your head. If it was just a standard isochronic tones theta track that shouldn’t be irritating if you have motion sickness.
♥ ← This set of tones with the bird calls from Aotearoa is keeping me awake while I finish an essay I've been working on for the past four days. Focus beats + sounds I associate with morning = wakefulness. Still craving the bed, but at least I'm not falling asleep at my desk. Thanks myNoise, without you I'd probably be listening to music and distracted.
Despite the lack of solid evidence of the effectiveness of binaural beats in producing brainwave changes, and that those changes can be effective in altering our conscious states, there do exist hours of recorded binaural beat videos available on YouTube. Some of these are just straight beats designed to ease the listener into various states by gradually varying the frequencies of the beats. A nice example of this can be found in a 90-minute video by Jody Hatton. Others embed the beats into a musical score, which some people find easier to listen to. Spotify has a whole playlist devoted to binaural beats. You can try these and many others to see if this is something that may be helpful to you. The soothing nature of the sounds may be what really helps, but that’s fine if you just want to relax and drift off to sleep. You can also find quite a few apps that generate binaural beats at your phone’s app store. If you want to relax and sleep just be sure to set the frequency in the theta range (4 – 7 Hz). Patients have reported to me that they felt energized or even anxious after listening to a few minutes of the beats, but this was usually because they were set to a high frequency like beta (13 – 16 Hz). Be sure to try listening to the beats for a short time and if they have a negative effect, just stop listening. If you find them helpful, that’s great, and you have a new technique that can be used to promote relaxation, something most of us can use. 
Binaural beats work by playing a different tone in each ear, and in the process the brain creates a “phantom tone” which is the difference between the two tones (for example if you play a 300 hz tone in one ear and a 310 hz in the other ear the brain will produce a 10 Hz phantom tone.) If this phantom tone is 10 hz the brain will gradually be led to a dominant brainwave frequency of 10 hz (this has been measured by EEG devices). If the tone is 7 hz the brain will gradually be led to a 7 hz dominant frequency, and so on.
When you listen to binaural beats/tones, you are actually listening to two slightly different pitched frequencies. Each frequency goes to each of your ears independently. When this happens your brain responds by creating a third tone, making up the difference between the two frequencies. This shift in frequency then shifts your brain’s consciousness and changes your state.
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.
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.
The objectives and inclusion criteria of the review were clear. Relevant sources were searched for studies, although the restriction to published studies in English meant that the review was prone to publication and language biases. The authors did not state whether steps were taken to minimise the risk of bias and error in the processes of study selection and data extraction (for example, by having more than one reviewer independently make decisions). The authors mentioned which studies were blinded, but it did not appear that study validity was systematically assessed, which made it difficult to judge the reliability of the review findings. The decision to combine studies by narrative synthesis appeared appropriate given the strong clinical heterogeneity between the studies, but the authors failed to quantify the size or statistical significance of the findings reported. The evidence presented appeared to justify the authors’ conclusions that further research was justified, but in view of the dearth of good-quality evidence and problems with methodology and reporting in the review, the conclusions regarding efficacy did not appear reliable.
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]
In the meta-analysis performed by Fox et al., several sources of bias were indicated which bring into question the validity of meditation studies which use neuroimaging. Fox et al. suggests a publication bias may be leading to the over-reporting of significant results.[18] Despite this, however, Fox et al. found "consistent differences in prefrontal cortex and body awareness regions" in "areas key to meta-awareness..., exteroceptive and interoceptive body awareness..., memory consolidation and reconsolidation..., self and emotion regulation..., and intra- and interhemispheric communication..." and that changes were significant with "moderate" global median effect size and "consistent and medium-sized brain structure differences."[18]

Anapanasati (Buddhist breathing meditation) Buddhist meditation Christian meditation Taoist meditation Dancemeditation Dhyāna (Buddhist meditation) Dhyāna (Hindu meditation) Islamic meditation Jain meditation Jewish meditation Muraqabah (Sufi meditation) New Age meditation Naam Japo (Sikism meditation) Neigong Pranayama (yoga breathing practice) Qigong Shikantaza (Zen Buddhist seated meditation) Silva Method Tantra Transcendental meditation (TM) Vipassanā (Silent meditation) Yoga Zazen (Zen Buddhist seated meditation) Zhan zhuang (Qigong standing meditation) 5Rhythms

Going deeper into a trance-like state of meditation, you enter the mysterious Theta state where brain activity slows almost to the point of sleep, but not quite. Theta is one of the more elusive and extraordinary realms you can explore. It is also known as the twilight state which you normally only experience fleetingly upon waking, or drifting off to sleep.
With brain wave entrainment technology, changing brain wave states is an instantaneous and effortless process. The 'periodic stimulus' can be sound, vibrations and/or light. We have found that we get the best results with blinking lights which are experienced through closed eyelids. This is only problematic for people with existing diagnosis of photo-induced epilepsy, as blinking lights can induce a seizure in them. The programs are enhanced with Deepak Chopra doing the narration along with holographic sound effects and original music composed and performed by Rudy Tanzi.
There isn’t really a one-size-fits-all track or frequency range which is right for all kids while doing homework. So that does make it difficult to recommend one thing in particular, and why I have a number of tracks for studying and focus. If they have already learnt and understood the information, but are just trying to commit it to memory for a test, then I would recommend an alpha track, like the Memorization Study Aid product I have with the 10.4Hz frequency you referred to. If they are still trying to fully understand what is being taught in a workbook, then I would recommend a track that is mainly beta frequencies, like my Study Focus tracks. In the middle, I have a number of tracks which use a combination of beta and alpha wave frequencies, like Study Booster, Study Enhancer and Cognition Enhancer. The last 3 use similar frequencies but deliver the tones and brainwave entrainment effects in different ways. As we are all wired a little differently it does sometimes take a bit of trial and error, to see what method or frequency range works best for the individual. These types of tracks are made for a general audience. In an ideal world, you would hook up to an EEG and see in real time exactly what a person responds to best, depending on the goal and current state of mind.
The brain will entrain to the strongest stimulus. If you combine binaural beats with isochronic tones, your brainwaves will entrain to the isochronic tones. If anything, when you combine the two I believe it makes the track less effective because it makes it harder for the brain to decipher between the two and synchronise to a single beat. There are lots of websites with compelling marketing about the benefits of combining the two together in some funky way, but I haven’t seen any research or lots of anecdotal feedback even to suggest it’s effective to combine them.
Many psychologists, doctors, teachers, and other professionals have endorsed the technology while personally taking advantage of the limitless benefits that accompany EquiSync's precisely designed brainwave synchronization/ entrainment technology. It is such a profound field of study that many of the metaphysical benefits, those beyond our current scientific measure and technological & philosophical understanding, have yet to be discovered.
James Austin, a neurologist, began practicing Zen meditation during a visit to Japan. After years of practice, he found himself having to re-evaluate what his professional background had taught him. "It was decided for me by the experiences I had while meditating," said Austin, author of the book "Zen and the Brain" and now a philosophy scholar at the University of Idaho. "Some of them were quickenings, one was a major internal absorption ­ an intense hyper-awareness, empty endless space that was blacker than black and soundless and vacant of any sense of my physical bodily self. I felt deep bliss. I realized that nothing in my training or experience had prepared me to help me understand what was going on in my brain. It was a wake-up call for a neurologist."
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.

I call the kind of intuitions and inspirations that come when we meditate and do these kinds of practices my “marching orders.”Okay, this is what I need to do. We’re not using our brilliant linear minds here; that’s not the place wisdom comes from. The place of wisdom is, again, relaxing into these states with loving-kindness, and then all the stuff can come out, whether we are dealing with our shadow issues or dealing with our light issues—the wisdom and gifts we haven’t yet brought forth that need to be birthed.


Binaural beats were first discovered in 1839. The effects of using audio instead of light for brainwave entrainment were noted in 1959. Oster’s research paper in 1973 brought attention to the use of binaural beats in a medical setting and this inspired a range of studies in the 1980s indicating very positive findings. The effects of brainwave entrainment using binaural beats has become of a hot topic of research ever since but despite their reported successes, they have never quite shook off the sometimes negative connotations of being an “alternative medicine”.
OK – so some of this is pretty common marketing hype. Consumers have become almost numb to such hyperbole. But still we see some of the common – almost ubiquitous – elements of pseudoscientific scams. The company claims that the device is “effort-free”, that the results are “rapid and long-lasting,” that it is the “most effective” method of its kind, and that it is useful for a broad range of applications (hey, why limit the market). I am used to such hype about dishwashing detergent, but find it intolerable when applied to a pseudoscientific device with medical applications.
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.
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.

There is a solution, which, although you may not have heard about it, has been around (and scientifically tested!) for decades now. By using binaural beats, you can ease your brain from its active state into a more restful state simply by listening to a different frequency wavelengths of sound in each ear. Because two different wavelengths are entering through two different entrances (your ears), that difference is perceived as a “beat” (though it may sound like a warble to some) that resonates at the frequency equal to the difference. The brain will entrain (match) itself to the beat produced by the difference in wavelengths. If the difference between the two wavelengths is less than seven hertz, your brain will fall into a state of deep relaxation, also known at the theta range.
The research may represent the bravest frontier of brain research. But depending on your religious beliefs, it may also be the last straw. For while Newberg and other scientists say they are trying to bridge the gap between science and religion, many believers are offended by the notion that God is a creation of the human brain, rather than the other way around. "It reinforces atheistic assumptions and makes religion appear useless," said Nancey Murphy, a professor of Christian philosophy at Fuller Theological Seminary in Pasadena, Calif. "If you can explain religious experience purely as a brain phenomenon, you don't need the assumption of the existence of God."
Binaural beats can easily be heard at the low frequencies (< 30 Hz) that are characteristic of the EEG spectrum (Oster, 1973). This perceptual phenomenon of binaural beating and the objective measurement of the frequency-following response (Hink, Kodera, Yamada, Kaga, & Suzuki, 1980) suggest conditions which facilitate entrainment of brain waves and altered states of consciousness. There have been numerous anecdotal reports and a growing number of research efforts reporting changes in consciousness associated with binaural-beats. "The subjective effect of listening to binaural beats may be relaxing or stimulating, depending on the frequency of the binaural-beat stimulation" (Owens & Atwater, 1995). Binaural beats in the delta (1 to 4 Hz) and theta (4 to 8 Hz) ranges have been associated with reports of relaxed, meditative, and creative states (Hiew, 1995), and used as an aid to falling asleep. Binaural beats in the alpha frequencies (8 to 12 Hz) have increased alpha brain waves (Foster, 1990) and binaural beats in the beta frequencies (typically 16 to 24 Hz) have been associated with reports of increased concentration or alertness (Monroe, 1985) and improved memory (Kennerly, 1994).
Cvetkovic D, Simpson D, Cosic I (2006). “Influence of sinusoidally modulated visual stimuli at extremely low frequency range on the human EEG activity“. Conference proceedings : … Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 1: 1311 – 4. doi:10.1109
Therefore we are very receptive to new technology products that promise to improve our lives, or solve previously difficult problems, because of some new scientific or technological advance. This has created, in a sense, a marketplace of consumers that expect to be dazzled with technobabble they don’t understand, backed by assurances of legitimacy by the citing of research and association with professionals or professional institutions, and offering significant benefits. We are all, in a sense, waiting for that next product to improve our lives, and many of us like to feel we are on the cutting edge – getting an advantage over others by being savvy early adopters.
"Given the popularity and effectiveness of meditation as a means of alleviating stress and maintaining good health, there is a pressing need for a rigorous investigation of how it affects brain function," says Professor Jim Lagopoulos of Sydney University, Australia. Lagopoulos is the principal investigator of a joint study between his university and researchers from the Norwegian University of Science and Technology (NTNU) on changes in electrical brain activity during nondirective meditation.
A study published in Electroencephalography and Clinical Neurophysiology by Paul Williams and Michael West in 1975 examined the brainwave states of people experienced in meditation while using photic stimulation, and another study by Leonard, Telch, and Harrington in 1999 examined the successful use of brainwave entrainment techniques for attaining meditative states in subjects.

Using a unique approach that combines the best methods from many different fields, the Neuro-Programmer 2 is an effort-free software application with unlimited potential and broad capabilities. Although it is incredibly simple to use, it remains the most effective self-help tool on the market today. Using NP2 is the single best way to achieve rapid and long lasting personal change.
Why is exposure to these soundwaves helpful to sleep and relaxation? Science shows that exposure to binaural beats can create changes in the brain’s degree of arousal. Listening to these sounds that create a low-frequency tone, research indicates, triggers a slow-down to brainwave activity—and that may help you relax, lower your anxiety, and can make it easier for you to fall asleep and sleep more soundly.
The results of using EquiSync for only 3 months have been phenomenal! Profound and positive changes have occurred , and continue to occur, in my being. These transformations have become obvious to family and friends as well. I am 71 yrs old and feel better than when I was in my thirties. My energy levels remain high with less sleep. I work out at the gym vigorously five days a week – bicycling and swimming are part of the regimen as well. I volunteer services at Hospice and nursing homes. My short term memory has improved to the point that others remark on my remembering their names after meeting them only once several weeks in the past. Sometimes I find that I’m reading fine print without my glasses. I spent the greater portion of my “productive” years as a monk but had lost the ability to meditate due to the development of A.D.D. Now my ability to stay focused and concentrate has remarkably returned and am reaching meditative states that I’ve not reached in years. Each new day is now seen as another opportunity to serve.
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.
In order to understand brainwave entrainment you first have to understand something about brain waves and electroencephalograms (EEG). Neurons are cells that communicate with each other through electrical conduction. When a neuron fires it creates a small electrical and magnetic field. These fields are far too small to measure by placing electrodes on the scalp, or even on the surface of the brain. The only reason we can detect the electrical fields of the brain is because many neurons are firing together – in synchrony. All brain waves that are measured by an EEG, therefore, represent a large group of neurons firing together.
The pitch frequency measures and describes what a beat sounds like, i.e. does the isochronic beat have a deeper bass sound, or is it high pitched and sharper sounding? The beat waveform frequency describes how many times the beat is repeating per second, i.e. how fast it is beating. You don’t really need to concern yourself about the pitch frequency, as that doesn’t have a direct influence on brainwave entrainment and doesn’t play a part on the measurement on an EEG. I only mentioned it because you were referring to humans not being able to hear below 20Hz. I change the pitch frequency just to suit the mood of the track. For tracks that are to be relaxing, for meditation or sleep, I tend to use a lower pitch frequency so it sounds deeper and more relaxing and I never have that lower than 100Hz. For an energizing, high focus track I might use a more higher pitched 200Hz isochronic tone, because that is sharper sounding and less likely to make you feel sleepy. That’s all you really need to know about the pitch frequency.
I haven’t seen any research relating to using brainwave entrainment/isochronic tones and bodybuilding, so I’m afraid I don’t know how effective it would be to help with that. I have a few different tracks for increasing energy but I recommend this 1-hour track, which would fit better than my shorter tracks for a training session: https://www.mindamend.com/shop/energy-and-motivation/high-energy-builder/. The effects from these tracks are mainly felt while you listen to them, so I recommend listening to the energy tracks while you are training/lifting weights etc. I don’t currently have any tracks to help trigger the testosterone hormone.
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.
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