What is Sound?

We are constantly speaking about music (well sometimes ketchup too) in our posts. Therefore I have decided to write about some key concepts or elements that create music.

Today we can start with the primary element of all music: "Sound"...

Generally it is not too easy to describe the phenomenon of sound without getting into physics but I will try to explain as simple as possible. If you ask me how I know this stuff is that it is purely related with my interest in synthesizers. Funnily when I was a kid, I thought that synthesizers were only musical instruments that could imitate the sounds of real acoustic instruments, obviously I was confusing them with sampling instruments (i.e. like an electronic keyboard playing a guitar sound). When I found out the enormous depth to synths, how they can shape sound or how one can generate an authentic sound even with the simplest synthesizer, I thought it was a good idea to check out how these marvelous machines worked. And it was that curiosity that allowed me to learn the stuff I will be mentioning. Maybe one day I will write the world of synths, who knows?

Sound:

One can make two definitions of sound that are perfectly correlated with each other.
First explanation approaches the sound with the involvement of physics and says that a sound is a pressure wave that is created by a vibrating object.
Second explanation is related with human physiology and psychology and it says that sound is a sensation that we experience when our ears are exposed to the above mentioned waves. Of course it is not our ears that convert these waves into sounds but a complex and marvelous system.

Briefly we can say that the waves or vibrations that are captured by our ears are transferred to our brains with an amazing flow where they are decoded and translated into sounds as we know them.

Now let's have a look at how sound travels. At this point please remember that sound can only travel in the air or in the water. Therefore we can easily claim that in space, where there is no air, there is also no sound (boring huh...).
It is the air molecules that carry the sound around. The vibrations that are created (imagine banging a drum) make the air molecules to start a similar motion. Since the air molecules move in a parallel direction with the wave itself we can say that the sound wave that is created is a longitudinal wave.

An example of a sine wave

It might be easier to visualize what's going on with the air molecules with the drum example.

When we hit the drum, the skin of the drum is stretched inwards. This causes the air to stretch in the same direction thus filling the space that is stretched after the hit.Keep in mind that the number of the molecules are still the same but just with the hit, there is more space for the molecules. This is called "rarefaction" (it is the area where the molecules look more comfy in the above picture).

Milliseconds later, after the hit, the drum skin automatically springs back, hence now occupying more space against the molecules. This is called "compression" and it is the area where the molecules seem squeezed. This movement is not a one time movement but rather a cycle depending on certain things such as the tension of the skin or the hardness of the hit. This cycle will be repeated until it dampens and will continue to make a sound until the skin is stabilized in its initial position.

We need to understand that the transmission that travels to our ears is not the air molecules themselves. It is the backward and the forward movement of these air molecules which we can call the oscillations.

Since we understood what sound is, we can now see the elements of sound.
Any sound in the universe (wherever possible of course), has 3 distinctive characteristics. These 3 parameters are; "pitch" (or frequency of the wave), "timbre" (tone color or the shape of the wave) and "loudness" (or amplitude).

From time to time we hear that the note A just above the middle C in the piano has a frequency of 440 Hz. This A (A440 or A4) note is generally used as a general tuning standard for musical pitch. But what does 440 figure represent?
The pitch or the frequency of a sound is a quality related with how high or how low that specific sound sounds compared to other sounds. Imagine a piano keyboard; the keys that are placed on the left hand side have much lower pitch than the ones on the right hand side. We call these low sounding notes as low frequencies or bass notes. On the opposite side of the piano placed are the high frequency notes or treble notes. But what is the parameter to create this difference? It is purely the frequency of each sound in reference to each other.
In more scientific words, a frequency of a sound is measured as the number of complete full oscillations per unit of time. The unit of this frequency is Hertz. If we imagine a 1 Hz sound, it means that the sound makes one oscillation per one second.

All of these would make much more sense if you can make an experiment with a tuning fork.
When you hit the tuning fork to a hard surface you might easily observe the vibrations being created (that is why the prongs of the tuning fork appear blurred).

As mentioned above, these vibrations create rarefaction and compression in cycles as waves. The waves move away from the sound source at the speed of sound which is approximately 330 meters per second. The pitch of a sound is determined by how quickly the sound wave is making the air vibrate. We can say that the sound is low if the oscillations are slower and high if the oscillations are faster over time.

For instance, our world famous A440 sound makes 440 oscillations per second.
So how does this scientific information translate into music? Each musical note has a pitch, that's how. Imagine a standard tuned guitar with 6 strings. If you pluck the A string (second from the top) and measure the frequency with a tuner, you should get a reading of 110 Hz (meaning the string is oscillating 110 times per second).

The frequency issue is very important in musical performances. If there is more than one musician involved, their instruments have to be very well tuned to play in line. Otherwise the same notes played on different instruments would sound out of tune compared to each other thus resulting an awful overall sound.
On the other hand, there is a concept called the "audible frequency spectrum" which represents the range a normal person can hear. Generally this range is between 20 Hz to 20 Khz (20 to 20,000 Hertz).
One last thing about pitch or frequency is the notion of the octave (one octave consists of 12 different sounds with 7 white and 5 black keys on the piano for example).
How do octaves relate with the pitch? In Western music that utilizes the equal tempered scales there is always a direct proportion between the notes. That is is why the system is called equal temperament in which the frequency interval between every pair of two adjacent notes has the same ratio (very roughly 6%).  Meaning each key (including the black ones) is almost 6% higher in pitch or frequency when going up to the right hand side of the piano, therefore leaving you with a perfect 100% or double the ratio when you come to the exact same note you started with but an octave higher (i.e. we know that A4 on the piano is 440Hz, if you go up one octave the frequency will be 880Hz and if you go down one octave the tuner will read 220Hz).

I hope the pitch topic is clear for you.

The second universal element of sound is "timbre" or the color tone of the sound. Timbre is maybe best explained by the comparison of different instruments playing the exact same note. We can differentiate the sounds of various musical instruments by their tone color or tone quality. It is fairly easy to identify that lets say the note C is coming from a piano or a guitar even though a tuner will give you the exact same reading.
Therefore in simple terms, timbre is what makes a particular musical sound sound different from another even these sounds have the same pitch and loudness (will come back to loudness). But how is that possible scientifically?
We saw a picture of a perfect sine wave above. In nature this type of wave is almost impossible to come by (as far as I know it can only be created with a synth). This leaves us with the concept of "waveforms".

As you can see from the above short video, there are basically 4 types of waveforms (of course we can argue that the number can go to infinity with their derivatives).
These waveforms are sine, square, triangle and sawtooth. What determines the color tone or timbre of each instrument or even any sound, is very much related with the shape of its waveform (therefore harmonics).

Also notice that the above wave lengths are quite similar (I did not check with a tuner but looks like the same frequency or pitch, therefore same musical note probably). However we hear the sound of each wave quite differently and that is only created by the different motions and vibrations of the air molecules surrounding the sound source. Unlike the pitch of a sound it is not possible to explain the timbre in a quantitative way. It is more a qualitative element of sound. Musicians can even have the possibility to change the timbre of their instruments by very basic tricks. A violin player can easily change the waveform produced by bowing differently or a guitar player can make a major change in the sound only with an effect pedal.
If you are interested in waveforms and wish to learn more (at least on a visual level), you may download the below app for your IOS devices.

Oscilloscope App for IOS

The last characteristic of sound is its "amplitude" or loudness in more general terms. I think this element is easier to grasp due to the fact that we are more familiar with it in our daily lives. Everyone knows that, for example, if you clap your hands more strongly you will hear a louder clap, or if you hit the drum with a drumstick instead of a chopstick, the sound will be more. How does this happen scientifically? Remember again our sine wave picture where in some areas the air molecules were more  compressed and the opposite in other areas. Amplitude is defined based on the area between peaks and troughs of one cycle of a particular waveform.

The more the air molecules are compressed or rarefied, the waves will be wider vertically, thus making the distance between the peak and the trough bigger that identifies the loudness of the sound (imagine hitting the drum harder and harder each time and try to visualize the impact on the air molecules).

The loudness does not work in a linear way. If you double the distance between peaks and troughs our ears will not hear the sound as two times loud. Another anomaly is that loudness can be related with timbre, meaning certain sounds sound louder to our ears even they have the same amplitude.

However these are all related with our hearing mechanism, our ears/brains and our perception of sounds.

Like pitch, we can quantify loudness as well. Generally the loudness is measured with decibels. Decibel is a logarithmic value that expresses a ratio for comparing the loudness of 2 different sounds. For example 0 decibel (db) is the threshold of hearing, 60 db is the sound intensity of 2 people talking, whereas a rock concert can go up to 120 db. What you can keep in mind is that each 20 db increase in the sound level translates to a 10 fold increase in amplitude (i.e. 20 db is 10 times louder than 0 db, similarly 40 db is 10 times louder than 20 db). With the same calculation we can reach to the conclusion that a rock concert is 1000 times louder than your normal talking so be careful with your ears in such places (I tend to carry ear plugs to loud concerts in order to limit the sound intensity to my ears).

I hope this post has helped you to better understand what sound is and what are its elements. I find it very interesting and miraculous to be able to hear the sounds that are encoded in all the good music we are hearing.
I believe the world would be an extremely boring place without any sound hence any music like the great examples below...