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I know that binaural beats are a controversial subject, as they might not work for everyone. In my own tests on myself I shuffled multiple recordings of binaural beats, with stereo headphones on, not looking at the frequency and resulting brain state advertised by each. I did, in fact, experience notably different mind states in these tests.

Binaural beats can be generated using carriers at any frequency within the audible range of human hearing. The frequency of binaural beats dictates the mind state that is being induced.

  • I'm wondering if binaural beats can be generated using carrier tones outside the range of human hearing?
  • And suppose that that works, do these binaural beats still have an effect on the state of mind? In other words, can you entrain your brain without being able to acoustically perceive the carrier tones producing the beats?
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    $\begingroup$ That's why I made sure to specify "tone" and "frequency". The "tone" is the frequency of the sound carrying the binaural beat, the "frequency" was the frequency of the binaural beat carried on the tone. So a tone of 1000hz could carry a binaural beat oscillating at, for instance, 4-7.9hz (dreaming sleep). The "effect" I stated is the actual entrainment of the brain due to the binaural beats. Does that help? $\endgroup$ – user1973385 Feb 22 '17 at 19:48
  • $\begingroup$ The answer to your question is not known yet. You might not be stimulating the auditory cortex consciously, but you can certainly stimulate areas of the brain using these carrier frequencies. See my comment on the accepted answer. $\endgroup$ – K Mmmm Nov 6 '18 at 19:57
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Short answer
No, infrasonic or ultrasonic sound cannot generate binaural beats.

Background
Binaural beats are generated in the brain and are associated with the frequency bands of the EEG. Binaural beats in the delta (1 to 4 Hz) and theta (4 to 8 Hz) ranges have reportedly been associated with reports of relaxed, meditative, and creative states, and used as an aid to falling asleep. Binaural beats in the alpha frequencies (8 to 12 Hz) are said to enhance alpha brain waves and those in the beta frequencies (16 to 24 Hz) have been associated with reports of increased concentration or alertness (source: Web US).

The binaural beat is not heard in the ordinary sense of the word - the human range of hearing is from 20-20,000 Hz and hence pretty much all the aforementioned frequencies cannot be registered directly by the auditory system. Instead, binaural beats are auditory brainstem responses which originate in the superior olivary nucleus of each hemisphere. They result from the interaction of two different auditory stimuli from opposite ears. The carrier frequencies have to be approximately below 1000 Hz and have to differ in frequency between one and 30 Hz. For example, if a pure tone of 400 Hz is presented to the right ear and a pure tone of 410 Hz is presented simultaneously to the left ear, an amplitude modulated standing wave of 10 Hz, i.e., the difference between the two, is experienced as the two wave forms mesh in and out of phase within the superior olivary nuclei (source: Web US).

Because auditory information needs to be sent to the brainstem, the auditory system is needed from the far periphery up to the brainstem. Thus, the hair cells in the inner ear are necessary to convey the information to the brain via the auditory nerve. Because infrasonic and ultrasonic sounds do not activate the hair cells and do not lead to auditory nerve activity, these sounds can hence not activate the brainstem and do not generate binaural beats.

Sources
- American Speech, Language & hearing Association
- Gray, Auditory System: Structure and Function. In: Neuroscience Online
- Web US

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    $\begingroup$ There is a big difference between ultrasonic and 1000 Hz. It might also be possible to use "transposed" stimuli (or SAM tones) to generate a binaural beat with a high frequency carrier. $\endgroup$ – StrongBad Feb 27 '17 at 15:03
  • $\begingroup$ @StrongBad there is a big difference, but that is what the question is, no? And the difference between infrasonic and 1k is an octave smaller than ultrasonic (-: $\endgroup$ – AliceD Feb 27 '17 at 15:33
  • $\begingroup$ Sounds outside of these frequency ranges can certainly stimulate nerves, if they have enough energy. You might not perceive them as sound, but you will still perceive them. See the Puerto Rico debacle where sound outside the human range of hearing was used to deafen congressman. See the debate over whether windfarms are harmful to people due to their vibrations. Acoustical vibrations are just mechanical vibrations; you might not "hear" the sound, but you can sense it with your "touch" sense, even submliminally. And this kind of stimulation might still have the same effect as binaural beats. $\endgroup$ – K Mmmm Nov 6 '18 at 19:54
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No, the carrier frequency for a binaural beat needs to be less than approximately 1500 Hz. The binaural beat arises because when two tones with slightly different frequencies are added, the instantaneous phase of the combination tone varies with time and has a period equal to the difference of the tones. The generation of the binaural beat therefore requires a carrier frequency at which the phase of the tone is preserved. The auditory system has amazing temporal acuity and can accurately encode phase information for frequencies up to about 1500 Hz. This information is key for localizing sounds based on interaural time differences. At really low beat frequencies (e.g., less than 1 Hz), the binaural beat can be heard as a fluctuation in sound location.

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