Sound Generation and Interpretation

I’m often asked, “How is music created?”[1]  There are two answers to this.  One is to look at it aesthetically, as in, how does a composer create music.  The other assumes that the person wants to know how music comes from a source and how our ears receive it and interprets it.  This post will investigate the second one.  I’ll give my answer to the first question in another post.

How Sound Travels From Source to the Ear

source to ear.png

The most basic understanding of music is that it is a special kind of organized sound (I’ll deal with how that specialized sound turns into music in yet another post).  Sound travels through the air from its source to our ear.

Let’s imagine some typical source of sound – any sound – but for this example, let’s imagine a viola (I could have you imagine a violin, cello, or double bass, but the poor viola is often neglected, so this is for the violists.  Your welcome).  The typical viola has four strings starting with the lowest (and thickest) string on the left.  Of course, you have to hold it so that the strings are facing you and the tuning pegs are facing the ceiling.  If you were to pluck this thicker string and then pluck any of the other strings, you will notice that it is the lowest sounding of the four strings.  If you were to look at the string when you pluck it, you might notice that it is not stationary.  The string vibrates back and forth.

These vibrations are in the form of waves.  Since humans are landlubbers rather than sea creatures, we hear these waveforms in the air.  To be sure, when we swim underwater, we can also hear sounds, but, since this isn’t our natural habitat, I won’t explore underwater hearing on this post (if you’re a dolphin or other sea creature, have a go).

This physical movement (vibration) disturbs the air around it (which you can’t see unless you’re in a very smoky room.  Even in this case, you are seeing the vibrating air acting on something else, namely, smoke).  The disturbed air moves from the source, through the air, to our ears.  Our ears translate this physical movement to electrochemical information that then travels to the brain.  The brain then interprets that information as sound, or music, depending on the context.

Sidenote:  Simply plucking a string is not, in itself, music.

Simple, isn’t it?

Here’s a more detailed answer:

A plucked string displaces the air.  The compression and expansion of the air happens at a certain number of vibrations per second, or cps (cycles per second), also known as HZ (a German dude named Heinrich Hertz, a physicist from the late 19th century).  The human ear[2] interprets vibrations between 20 Hz to 20,000 Hz as sound When you hear the piano, you aren’t hearing only the pitches between 27.5 Hz and 4186 Hz.  The piano, voice, saxophone, cello, etc., have unique combinations of frequencies that help you identify the instruments[3].

Four points here:

  1. The 20-20,000 Hz range is the normal range for a healthy person[4]. The older we get, or if we experience some kind of trauma, the narrower this range becomes.
  2. The usable range is much narrower. Human speech, for example, is roughly between about 82 Hz to about 255 Hz.  The range of a piano is from about 27.5 Hz to about 4186 Hz[5].  If you were to play the highest and lowest keys on the piano, they might not make a lot of sense to you out of context (outside of playing music or as part of a scale).
  3. The highest pitches up to 20,000 Hz can be painful to experience. Imagine the highest notes from a piccolo (around 4096 Hz) and you get the idea.
  4. Although we can detect sounds between 20 and about 27 Hz, it sounds more like fast thumping. Although we can’t hear below 20 Hz, many animals can.

As stated before, these soundwaves travel from the source to our ears.  What is it that translates the physical movement of the air to the electrochemical movement that goes to our brain?

Colloquially speaking, it’s your eardrum.

When you were young and foolish, you might have stuck something into your ear, like a cotton swab.  If you’ve been careful, you would have noticed that there is a point where this insertion stops.  If you’re not careful, the result will be somewhere between pain and deafness.  That point where the insertion stops is your eardrum[6].  In science-speak, the eardrum is called the tympanic membrane[7].

There is more to the anatomy than a membrane.  The soundwaves enter the ear and hit the tympanic membrane which moves back and forth and transmits the movement to the cochlea.  The cochlea is a spiraled conical chamber that has in it, among other anatomy, very fine hairs.  These hairs transmit the physical, or mechanical, energy to electrical energy that is transmitted to the brain via the central nervous system.  Okay, that is really over-simplified, but it works.

The Perception of Sound As Music

This is a little more difficult to explain as it involves culture.  What some cultures hear as noise, other cultures hear as music, and vice-versa.  Even within cultures, there may be sounds that, for some populations, are musical, while for others, it is noise.

Wait.  It’s not difficult to explain.

Elements of Music

In later posts, I will describe the following terms in more detail:

  • Musical pitch
  • Duration
  • Timbre
  • Loudness

 

[1] Actually, I’m never asked this, but let’s pretend…

[2] To compare us with other animals, check this out:  https://en.wikipedia.org/wiki/Hearing_range#/media/File:Animal_hearing_frequency_range.svg

[3] When you hear the piano, you aren’t hearing only the pitches between 27.5 Hz and 4186 Hz.  The piano, voice, saxophone, cello, etc., have unique combinations of frequencies that help you identify the instruments.

[4] For humans, 20-20 KHz (Kilohertz) is the audible wavelength.  When the waves are at a higher frequency, they are perceived as light.  For example, red and its shades are in the 400 to 484 THz frequency while violet and its shades are in the 668-789 THz (Terahertz) range.

[5] A sound-producing object, such as a string, membrane, or hollow tube, produces a fundamental pitch depending on its size.

[6] Please don’t try this at home.  You might lose all or part of your hearing.

[7] The snare drum, tom-toms, timpani, bass drum, djembe, tabla, dumbek, kendang, bedug . . . are just some examples of instruments where you strike a stretched membrane to produce a sound.  This class of instruments are called membranophones.

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