Briefly, sound is a vibration and that vibration holds a specific frequency. Air itself for instance, is not sound, as you probably already know. Sound occurs when the molecules come in contact with those of any other object and cause longitudinal waves, (the kinetic molecular motion can determine how large these longitudinal waves are) entering the outer ear, then to the ear canal, which the eardrum senses the vibration and it is then sent to “three tiny bones in the middle ear…malleus, incus and stapes.” These individual bones have their specific purposes such as the amplification of sound. This sound is sent to an organ called the cochlea, which apparently is shaped like a snail and is filled with fluid! The cochlea is separated into two portions which serves significant to the function of hearing, as the vibration causes the fluid in the cochlea to move like a ripple which moves against the partition of the cochlea or the ‘basilar membrane’ some small hair cells move along with this wave.“As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cells, creating an electrical signal.” The signal is finally sent from the auditory nerve then to the brain, which is how sound is perceived. Although there are more pieces to how sound is heard, which I won’t go into too much further detail (but if you find the function interesting, I suggest reading other explanatory articles regarding it.)
Now that we know how hearing works, let’s delve into overtones. The larger the frequency is in, (Hertz) the higher pitched it will sound, on the contrary, the lower the frequency is, the lower the pitch will be. Static or white noise is several frequencies occurring all at once. A basic analogy would be the illustration of a piano continuum. Imagine all keys are being pressed simultaneously. There is no distinction to the sound, it’s indecipherable. The theoretical piano does have its limits, as in nature or whatever is emitting the noise has its own bandwidth or spectrum.
When one dominant frequency, or pitch is played, this is a fundamental or root which is the lowest portion of a harmonic series. If you hammer down a note on the piano and listen carefully, you notice there are other vibrations and notes, despite only playing ‘one note,’ for instance you hear overtones, which are notes of higher pitch than the initial root note. Why does this happen? The sinewave or the vibration vibrates other strings of an (acoustic) piano because the vibrations align and can be thought of as multiples. To prove the existence of these notes, you can use (audio spectrum to notes analyzer) software to monitor sounds, and become amused. The stronger lines as evident by the picture demonstrate the dominant notes, and the more opaque colors above are the overtones. More specifically in a note, these are harmonics, because they are significant to a specific series and are naturally recurring.
In basic music theory the image above here is an F triad, a chord with three notes. The F is considered the fundamental because it is the note that supports the rest of the triad. If you count the placement of the white keys Including F to C notice there are five notes. The F is the root/fundamental, the A is a 3rd and the C is a 5th. By adding more equally spaced notes in this consecutive sequence, these frequencies overlap when one note is played, no matter what instrument, voice, or singular sound.
What is very intriguing in my opinion, is that you, yourself can listen to your own overtones, produced by your voice. Basically by singing a resonant note and altering mouth shapes as well as vowels, you can hear a prominent whistle and manipulate this overtone. This might sound odd to sing and move two notes at once intentionally, but it is very possible.
How do you sing a resonant note, as opposed to just singing a note, when trying to hear an overtone? Resonance is the quality of a sound, it is full, pristine, and sustained. To achieve resonance when singing, try singing one note through different vowel shapes like: ee, ah, oo, ou. While singing this, widen the corner of your lips as if you are smiling, then slowly round your lips (this darkens the sound, while widening brightens the sound). Resonance is like the sweet spot of a sound, or like placing your hand in the water before a shower to determine if it is the right temperature.
What significance do overtones bring to instruments? Overtones distinguish the timbre of instruments or the color of its tone, for instance, a c4 on a piano sounds different than a c4 on a guitar string, despite being in the same octave and representing the same note. The emphasis on specific overtones over others specify the tone.
All in all, overtones are an interesting segway between physics and music or auditory science whatever you want to call it. Although it may seem unnecessarily complicated, briefly understanding its functions adds another layer of appreciation to music. Overtones place meaning to sound, than static. Sound with purpose is objectively beautiful, whether it be dissonant or consonant (pleasing sounds), as effortless a sound may seem there are endless explanations which mostly make no sense, but once some of it makes sense it feels epiphanic.