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When the beat frequency is very low, we hear periodic maxima and minima. Our ear cannot perceive a on-off like sound when its frequency is more than 10 Hz. So, beat frequency in audible range will not appear like a sound going on and off. Do we perceive any special when the beat frequency is in the audible range (20 to 20000 Hz) ? (Let us assume that we can perceive every sound whose frequency is in the audible range)

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marked as duplicate by sammy gerbil, ACuriousMind Oct 6 '18 at 10:26

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ Those of use who have poor pitch use beating amplitudes to tune our guitars. $\endgroup$ – JEB Apr 13 '18 at 16:39
  • $\begingroup$ There is a problem in Hewitt's book, stating that one would hear beats between two ultrasound sources at 100 kHz and 102 kHz. Of course, this was not based on observation. $\endgroup$ – Pieter Apr 13 '18 at 16:54
  • $\begingroup$ @Pieter: and how do you know this was not based on observation? Consider this Wikipedia article. $\endgroup$ – Peter Shor Apr 27 '18 at 17:59
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    $\begingroup$ @PeterShor Nonlinearities and very high levels of ultrasound (over 100 dB) are needed to create anything audible. (I have tried with our 41 kHz piezotransducers, I can see the beats with a microphone on an oscilloscope, but do not hear anything. None of my students either.) $\endgroup$ – Pieter Apr 27 '18 at 19:06
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    $\begingroup$ @Pieter: so clearly our ears are not non-linear enough. Interesting. $\endgroup$ – Peter Shor May 3 '18 at 19:18
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I think that there are ranges of perception.

If the beat frequency is low the two notes are very close together. We hear the beats of the envelope and probably perceive the average of the two notes as the pitch. As someone mentioned this is how we tune our instruments (not just guitar).

If the beat frequency is high the notes are far apart and we likely hear each note separately, not perceiving the beat or the average tone. Humans have a bandwidth for pitch discrimination that is dependent on both the relative different in the tones and the frequency of the average tone.

In short, we cannot easily distinguish two pitches if they are both very low (bass) while we can more easily distinguish them at high pitch (soprano). Hence from a music theory point of view it is not wise to put minor seconds in bass harmony, use large intervals, while small interval harmony works in upper registers. The text Physics and the Sound of Music by Rigden explains this phenomenon quite well.

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