What is Sound? - On Music

Though I want to move to the topic of ‘musical note’, which is the very start of subject matter, I realize we can not go ahead with no discussion on few fundamental physical properties of sound. 

Consider a simple example of books on a shelf. You want to read a book, you ask your friend to bring it from the book shelf. Now it is your responsibility to tell your friend which book you are looking for. 

You have some descriptions:

“The book that has black cover”
“The Oxford dictionary”
“The Oxford press dictionary, latest edition”

Likewise, you can name the author, title of the book, location of the book; it all depends. What your friend could understand about. Here what property of the book you use to describe is that all matters. Same way, sound has certain properties to describe it. Not every book in a library is similar, the same goes with sounds. 

I suggest having a glance at the last pictureof previous chapter.

On left what we see is tuning fork which is used to produce sound waves in basic physics experiments. As we discussed earlier, sound waves are the waves which propagates forth and back way. So in the picture we see vertical lines, the distance between the vertical lines vary to show the compressed and the uncompressed areas of the medium. Let us not dig into this much.

Unfortunately we don’t have a video here, but I promise to look into that.

Assume that the vertical lines are constantly producing the tuning fork and move forth. So we have a stream of vertical lines as the picture describes. Let us now call the “vertical lines” as wave particles for convenience.

So we have a stream of wave particles that flows from the source (in our case the tuning fork). You compare this to a water stream from a water source. When there is stream of wave particles that move in air (medium), being disturbed by vibration of sound source. This disturbance is represented by compressed (tight) and uncompressed area of the stream. It is exactly what happens when our Chennai city bus driver hits the break when and where he wishes. 

Frequency is the number of times the sound source moves back and forth (vibrates). If our bus driver hits his break four times in a second (no harm, let us imagine), frequency is four. 

In our illustration, the number of times the compression of wave particles created in the stream, the number of compressed (tight, dark) areas represents frequency of the sound the tuning fork generates. 

In our illustration the wave length is shown, click to enlarge the picture. The wave length is the distance between mid points of two consecutive compressed areas. Sorry but the way of scientific definition.

The relation is quiet simple that Physics assures that speed of sound waves in air is not changed generally. If we multiply two numeric values, Frequency and Wave Length we get speed of the sound wave. As the speed reminds constant under normal conditions, one can logically understand a frequency increases, wave length decreases and vice versa. 

If you like above paragraph or not, please try to get an idea of this relation between frequency and wave length as we are going to discuss many interesting, fascinating, amusing aspects of music, using this basic properties of sound.

Frequency of the sound determines shrillness of sound. A frequency increases we reach higher pitch tones. A Cello produces sound that is thicker in tone than the sound of Violin. This is because the sound produced by Cello has lower frequency and a Violin is capable of producing higher frequencies. 

Check the following sound samples of a Cello and Violin, both are very similar in every aspect except the size.

A child’s cry has higher frequency than a female voice; a female voice has higher frequency that male voice.

If you consider double bass it is capable of producing sound that has frequency lower than of a Cello, in other words, sound that has longer wave length than of a Cello.

In next episode, we will discuss how music is different from noise.