Sound - Whoa.
In a sense, sound is the gateway drug to learning how to audio engineer. No one can become any type of engineer without understanding the fundamental basics of what puts “audio” in audio engineering. In this first little bit we’ll go through what sound is and how it moves through space and what the characteristics of sound are.
For starters, sound isn’t necessarily… a sound. It’s more of a range of vibrations that is audible to your ear. These vibrations can be created by any source that is capable of emanating vibrations. These vibrations cause the medium around it to vibrate creating an audible sound. These vibrations are able to travel through a medium in traveling longitudinal waves creating different pitches, which we’ll explain later.
As these vibrations - which from this point we can safely call “sound” - move through a medium - we’ll say air for right now - they compress and refract. An easy way to imagine this is by “throwing a rock into a pond”. We can call the rock the source and the pond our medium. Throwing this rock into the pond would create ripples which we can use to resemble the vibrations or our traveling longitudinal waves that we mentioned. These waves are collections of dense molecules that are being pushed together as other collections of sparse molecules expand. Collections of dense molecules being pushed together is called compression and leads to an increase in pressure. Refraction happens when an area where fewer molecules are pulled apart, or expanded, leading to a lower overall pressure.
Another good example that gets thrown around a lot is “the slinky example”. Imagine a closed slinky in your hands. As you part your hands the slinky begins to expand, the rungs separating from one another slowly and maybe even wiggling just a little bit. Not any significant movements, but a gentle wiggle. Now you’ve got your hands parted at about shoulder’s width - slinky and all. You begin to deliberately create movement on one end - you could call this a source - and you start to notice a ripple move down the slinky. A small one, maybe just a little crest, but you recognize it. You make your movement more deliberate and you begin to see a constant wave pattern. Try and imagine - as source movement moves through the slinky it begins to refract, dropping the slinky down as your wrist directs it. The trough, or lowest point of a wave, expands to its furthest point and compresses into itself, shifting itself back to its origin point. As you move your wrist upwards, the section you were observing begins to move upwards, compressing back into itself and starting to form a crest as it reaches its highest point. As you see this wave cycle happening you notice that as this one half goes up the other half goes down. You start to move your wrist faster in turn making the slinky move faster and with more waves. You see a few now, four or five, and you can see they are pretty consistent in size and shape and distance. The wavelength, or distance between two consecutive wave crests or troughs, is representative of pitch. While you don’t know exactly what pitch is yet, you can see that when you move your wrist faster or slow, the waves change size and shape and the wavelength gets longer as you move slower and shorter as you move faster. Crests begin to form faster and compress at the top creating ripples that travel down to the trough and lose gumption as they make it to the most expansive part of the trough.
You start to realize now that sound IS like a slinky in a sense - at least the way it moves. A source creates a vibration that causes the medium around it to vibrate creating a pitch that is audible to the ear. Your hand creates a motion in the slinky that creates a movement in one part of the slinky that moves throughout it that is visible to your eye. Hell, if you try really hard and have a steady hand you could probably hear the slinky make some sort of warbly metal noise while it does all this. This example, the pond example, most examples of waves in their most natural environments can be broken down into some sort of situation in which it resembles sound. Sound is merely a participant in what is called wave theory, something that we won’t explore until later on in the series of this website but is very important to sound as a property itself.
------ Sources ------
- Tim Dittmar, “Audio Engineering 101: A Beginner’s Guide to Audio Engineering”
- Tim Dittmar, “Audio Engineering 101: A Beginner’s Guide to Audio Engineering, pg. 7”
- https://method-behind-the-music.com/mechanics/physics/ Method Behind the Music, “The Physics of Sound Traveling Waves”
- As always, our personal experiences and past trainings