What makes a sound?

Well, lots of things obviously, but I’ve realized that in order to better understand the tools I’m now trying to learn, I need to also understand the underlying principles of what Sound really is. Therefor I will start adding some posts here about the physics and theory of sound. Hopefully writing it down like this will reinforce my own learning and also benefit others out there wanting to learn about this things. Almost all of this information is available via wikipedia and other online sources (but there are also sprinkles of knowledge that is not so readily accessible so please stay tuned…).

As noted I am only just learning about this now so please feel free to point out any errors via the comments…

A definition of Sound

So what is sound? Sound can be defined as essentially two different things. 1. The ‘experience’ of sound, which is what we have when we hear a sound, and 2. the physical movement (vibrations) of air produced by a sound source, also known as sound waves. The former refers to the quality of sound while the latter is more concerned with how to make sounds with different characteristics.

Different types of instruments produce sound waves through different mechanics. The sound from a guitar for example is produced when the player hits a string, which by vibrating creates sound waves. With a flute you cause the air inside to vibrate by blowing into it. In either case, vibration is the key.

At a high level, the characteristics of a sound are determined by 3 factors; Pitch, Timbre and Loudness. Each of these qualities are in turn determined by a range of factors and I intend to write a more in depth post about each. For now, here’s a quick introduction to each.

Pitch

The pitch is what makes a sound appear ‘High’ or ‘Low’. It is determined by the number of vibrations created during a set period of time, which is also known as the frequency of the sound. The higher the frequency, the higher the pitch and the ‘higher’ you perceive the sound. There are a couple more things we need to cover about pitch such as Wavelength, Resonance and the relationship between the material properties of a sound source and its perceived pitch, but I will cover those in a deeper dive later.

Timbre

Timbre is a french word that means (loosely translated) ‘tone color’. It is the quality of a sound that allows us to tell the difference between two sound sources producing a sustained sound at the same pitch. Thus, even if to instruments are capable of producing a sound at with the same (theoretically stable) pitch and loudness, we can tell the difference between them because they will have different tone color properties. Timbre is a debated term that tries to describe and define an elusive property of sound. Important factors that make up distinct timbre include spectrum and envelope. As with pitch, the physical properties of a sound source such as material and size also influences its timbre. I have only begun to understand the properties of this quality, but I intend to write up a longer note on this soon.

Loudness

Loudness is often mistaken to simply mean the volume of sound, but there are plenty of other, more complex relationships between the character of a sound and it’s loudness. The perceived ‘strength’, or the relative position of a sound on a scale from ‘quiet’ to ‘loud’ is a common, formal definition of Loudness, but in order to fully understand why we experience different levels of loudness it is important to also understand how loudness is defined and how it relates to pitch and timbre. Factors that play an important role in determining loudness include frequency, bandwidth and duration. Together those factors help determine the loudness contour, or envelope of a sound, which in turn defines its Loudness. Again, more on this in a dedicated post.

Finaly

As is obvious from the above, the 3 qualities mentioned are deeply intertwined and all effect each other in many subtle ways. Hopefully by studying these relationships I can better understand how electronic synthesis of sound works and how to create the kind of sounds I want. I know this will be an important step in getting the music I hear in my head through the tools and into actual songs…

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