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I hope I'm using the term correctly... I think the overtone series is what one hears based on a fundamental. For example, if a C3 is played as the fundamental, the first overtone would be the octave above that, followed by the fifth above that, etc.

My question is, is it possible for humans to hear overtones from a fundamental that is below human hearing? If the lowest tone a human can hear is at about 12Hz under ideal conditions, can a fundamental tone vibrate, for example, at 8Hz (which, in theory, we cannot hear) and produce overtones at 16Hz, 24Hz, 32Hz, etcetera that would be audible to the human ear? (Then, if that is possible, I wonder how much of what we hear falls into that category.)

Not sure why but I've been curious about this for a while and have not been able to find a good answer.

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    Not only is this possible, it's the basis of a certain trick speakers use to recreate low frequencies - look up "missing fundamental effect"! – user45266 Oct 26 '20 at 20:01
  • @user45266 do they really need to implement it? I mean, if the bandwidth of a speaker won't reproduce the fundamental, it may still reproduce the overtones if they are in the range of frequencies they can reproduce, thus recreating the bass by the MFE… So you just need to go low enough to reproduce the harmonics of the lowest bass sound you want to achieve, but there is nothing more to do. Or am I missing something? – Tom Oct 26 '20 at 20:57
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    @Tom This effect has been deliberately used for speakers, see this source. Though of course, faking low frequencies using psychological tricks is still not recreating low frequencies, and audio engineers would definitely hear the difference. I have used the software equivalent of this by accident and it was clearly inferior to true bass reproduction. – Edward Oct 26 '20 at 21:24
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    @Edward yes, but what I do not get is how are they using this effect actually. Missing fundamental phenomenon will occur as long as you have enough harmonics. If the speaker can reproduce can reproduce these harmonics, nothing more to do! Could be a real phenomenon always occurring sometimes used by manufacturers to justify their lack of bandwidth… – Tom Oct 26 '20 at 21:51
  • @Tom The MaxxBass software manual I linked says that it generates harmonics. Here's a better source for the MaxxBass speaker- "MaxxBass process generates higher harmonics from the low fundamental frequencies below the (set) MaxxBass Frequency, and adds them back into the signal" – Edward Oct 26 '20 at 23:01
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If the infrasound has overtones in the audible range, then yes you can hear them. The overtones could be completely separate waves independent from the fundamental - the ear can't tell, even though it tries to figure out which waves come from the same source by grouping together waves that appear to move as a tightly correlated single entity. (Which is the reason why you should avoid having parallel fifths or octaves in N part harmony. Once the voices start moving together by the same steps, the ear puts all of the unison-locked partials/overtones in the same bin, and doesn't distinguish the voices as separate anymore, so your four-part harmony becomes three-part harmony all of a sudden.)

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Yes, this is possible, but this accounts for a minority of musical sounds that we use. One example in practice is the electric bass guitar, when tuned very low. Here's an extreme example of a bass tuned to C#0, or 17.32Hz. You can clearly hear the bass, although its pitch might be hard to discern. More commonly, you might hear a bass tuned to B0 (30.87Hz, within the human hearing range) but played through speakers that cannot reproduce that low of a note, so you will only hear the harmonics.

Some organs can reach this low as well. Here's an example of an organ playing very low notes down to about 16Hz.

Also, tubas can reach very low, and the very low notes are called "pedal tones". This goes down to about 14.57Hz. This goes down to about 21.83Hz.

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https://en.wikipedia.org/wiki/Missing_fundamental

When the missing fundamental is in the hearing range, most people will "hear" it. Human brain is pretty good at filling in usual things when they are missing. It does require training, but most of us get this training at early age without knowing it.

When the fundamental is lower, however, a lot of people will not have a previous experience to relate the overtones to.

On the other hand, a person used to matching a wide range of vibrations to sounds (like, say, operators of different rotary machines and engines) could pretty much "feel" the base frequency.

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It's going to be quite dependent on what the original sound source is. Each instrument has its own individual timbre, which will contain different overtones along with the original note, in differing strengths. That's why each instrument sound unique to us, even when each plays exactly the same pitch.

So, yes, providing those overtones are within human hearing range, they will be heard. Which ones will be audible, though, will depend on, as stated previously, what the instrument is that it's played on.

That may sound strange - why would anyone make or play an instrument that could produce sounds, the fundamentals of which would be inaudible?! That's hypothetical, somewhat like the question!

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Yes. As long as the frequency produced by the overtone is within the audible range, it will be heard.

0

Many answers so far have answered an opposite question - can we reproduce just the harmonics of a low note and 'hear' the fundamental. That's an easy 'yes', and it's the practical basis of e.g. an 'acoustic bass' stop on an organ where multiple ranks of pipes tuned to the harmonics of a low note give the illusion of that low note being played.

The actual question - hearing the harmonics of an ultra-low note that IS actually produced - occurs less frequently in the musical world. Instruments that play such notes would be large (and therefore expensive). Why would we bother to make one? So we need to look at non-musical and natural sources of infrasound.

There certainly seem to be examples of infrasound that DON'T produce audible harmonics - the whole point of low-frequency sound as a weapon is that it isn't audible (or, apparently, particularly practically effective).

And examples of ones that do - e.g. wind turbines.

"The noise has a discrete frequency character, consisting of the blade passing frequency, and a number of harmonics." Infrasound Emission from Wind Turbines, Jørgen Jakobsen, Danish Environmental Protection Agency

But, to return to the question, yes, an infrasound source can have overtones in the audible range, and if they're at more than negligible amplitude, we'll hear them.

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As far as I understand overtone singers produce higher pitches by closely alternating lower frequency tones. So there is a whole area of application in human voice for your theoretical question.

I would like to point out that even the opposite is also possible and has been used, e.g. in Alfred Hitchcock's classic movie "Birds". It is the so called "Trautonium" built and played by Oscar Sala which produces undertones along the same principle.

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I have a special guitar that plays zero octave. Its overtones into distortion push the audible portion of the sound into the midrange. You can do sane thing with synth that has lot harmonics its zero octave tones are audible in the range of hearing . Thete so much cool stuff you can do with this , for example tweaking ypur kick drums to be audible on laptop speakers when recording your albums

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