Fundamentals of Sound in Physics (and How That Translates to Music)

By Derek Martinez

Though we credit most of our experiences with sound and music to transduction, the actual process of how our brain understands and processes stimuli, we must equally give as much credit to the actual creation of sound in physics.

For this article, the example of how a tuning fork creates sound will be used as it is one of, if not the simplest sounds in nature. If you are not familiar with how a tuning fork is used, this is essentially what it does.

Tuning Fork Physics

Image Credit: "File:Mode Shape of a Tuning Fork at Eigenfrequency 440.09 Hz.gif"by Sudoer41 is licensed under CC BY-SA 4.0

When you strike the tuning fork against a surface, preferably a hard one, and hold it to your ear, you will hear a vibrating, ringing pitch, similar to a bell. Tuning forks are commonly used in medical exams to assess hearing, and also as a method for musicians to tune their instrument or “tune their ears” to a certain temperament. The sound produced from a tuning fork is caused by periodic changes in air pressure at one’s eardrum, and these air pressure changes are caused by the vibrations produced from the tines of the tuning fork. If there are no changes in air pressure around the ear, our brain interprets it as silence. The high and low pressure waves that travel through the air to the ear pushes and pulls on the eardrum at the same rate that the fork produces the waves.

Compressions are the regions in which there is high pressure, and rarefactions are areas where there is low pressure. In the image above, the moments where the tines are closest are rarefactions, and the moments where the tines are furthest are compressions. These regions are then propagated through the air, carrying the sound signal to different locations.

Physical Properties

In this diagram, the upper wave would be a higher pitch and the lower wave would be a lower pitch

The rate of periodic pressure change is called frequency, which we hear as pitch. In a musical context, frequency would translate to our ears as tones/notes. Though western music has 12 individual notes, (including enharmonic equivalents) that obviously does not mean that there are only 12 frequencies that exist. That would be very boring. Frequency is measured in hertz, (Hz) which is cycles, or oscillations per second.

On string instruments, (say a viola because they’re underrated) if you were to place your finger on a string and then play it, and then in the same place wiggle your finger even slightly and play again, you would hear an audible difference, even though you’re technically playing the same note. This is because it has a different frequency, and thus a different Hz value. Hertz are also used in music to tune to a different frequency from normal, such as 432 Hz, which is slightly lower than what is considered the universal tuning system, 440 Hz.

The strength of the pressure fluctuations of waves is called intensity, and our brain interprets it as loudness. In music notation, intensity would essentially be the same as dynamics, which is how soft or loud an instrument is playing at a certain moment. Intensity is measured in decibels, (dB) the threshold of hearing for decibels is 40 dB up to 120 dB, which is known as the threshold of pain. (ouch)

Onset is the time when an actual sound begins, and similarly, duration is how long we can hear the sound, which is measured in seconds. In music, duration and onset is notated as rhythm, but is instead measured as how many beats a note contains.