Page 44 - Zone Magazine Issue 015

STUDIO TIPS 005
The Fundamentals of Sound Pt. 1 >>>>>>>>>>>>>>>>>>>>>>>>>>>>> Daniel Daly >>>>>>>>>>>>>>>>>>>>>>>>>>>
In this article, you will be introduced to the Basics of Sound and the theory behind what makes up sound. This can be a very complicated subject to understand, so instead of showering you with lots of scientific jargon and trying to condense everything into one article. I will instead, spread this over the course of a few different articles, to make sure I cover everything without overloading you with too much information and potentially losing your interest.
Before we jump into the world of sound waves and sound synthesis, we first need to understand what sound actually is.
Sound is simply a vibration of Gas, Solid or Liquid e.g. sound moving through water. Sound is also a Perceptual Phenomenon, in the sense that it requires the Human Hearing System, to decode the sound. Your ear first picks up the vibrations, then your brain recognizes it as having three properties, that help distinguish one sound from another.
These properties are Pitch, Loudness, and Timbre. Sound can be viewed mathematically as a combination of one or more Sine Waves as seen in fig. 1.
If you can imagine sound traveling through air, the vibration (oscillating) of air molecules between its minimum and maximum value, is what the ear perceives as sound. Fig. 1 shows a diagram of a single cycle of a Sine Waveform. A Sine Waveform is a mathematical concept, that can be used to represent an oscillation of sound that repeats over time. As you can see in the example, the Sine Waves amplitude or loudness reaches a maximum of +1 and a minimum of -1. Sound waves also have a beginning and
end cycle. This means where the sound wave starts at the zero crossing point, completes one full cycle and then repeats.
The number of times a cycle repeats over time is what creates the frequency of the sound. In terms of sound waves, it is the number of times a wave completes a cycle in 1 second, that determines the frequency of the sound. You may have seen sound described in units called Hertz (Hz). What this simply means, is that if a sound wave repeated its cycle 200 times in 1 second, the frequency of the sound would be 200Hz. If we now look at fig. 2, we have an additional Sine Wave added to the graph. The second Sine Wave shown in green, completes 2 cycles in the same space of time, that it took the first wave to complete 1 cycle. This means that the frequency of the second wave is double that of the first. So if we take the example of the first wave being 200Hz, the second wave would now be 400Hz.
The range of human hearing spans from roughly 20Hz to 20,000Hz or 20kHz (kiloHertz) for short. This can differ from person to person, depending on a number of different factors such as age, hearing loss etc. A visual representation of the frequency spectrum can be viewed using a Spectrum Analyser. A Spectrum Analyser displays The Frequency vs. The Amplitude of the sound.
Fig. 3. is an example of a Spectrum Analyser displaying the frequency and level of a sound wave. As mentioned earlier, the sound has 3 perceived properties, Pitch, Loudness, and Timbre. We have already spoken briefly about frequency and its unit of measurement, Hertz (Hz). But if we were to look at sound in terms of Pitch, it would be
closely related to the frequency of the sound, but not entirely the same. Pitch can be broken down into a unit called Octaves, which contain smaller units called Semi-Tones. An Octave contains 12 semi-tones, which corresponds to each key within one octave on a keyboard. A sound which is twice the frequency of another is said to be one Octave higher. For example fig. 2 shows 2 sine waves, one at 100Hz, the other at 200Hz. The second sine wave of 200Hz could be described as being one octave higher than the first one, as it is exactly twice the frequency of the first.
Loudness is measured in units called Decibels (dB). If a sound wave has a larger Amplitude, it is perceived by the brain as being louder and the opposite if the sound wave has a smaller amplitude. If we look at fig. 2.1, you will notice that the second Sine Wave is oscillating at a lower amplitude than the first Sine Wave. Therefore, the first Since Wave will be perceived as louder.
Lastly, we have the concept of Timbre. Timbre to put it simply is the “Tone” or “Texture” of a sound. This is what helps you distinguish between the sound of a guitar playing a G chord and a piano playing a G chord. To explain what Timbre is, we need to look a bit deeper into what makes up a sound. A sound is made up of tones. If we take a single Sine Wave, for example, this is known as a pure tone or simple tone, as it is made up of only one tone. Any sound which is made up of more than one tone is called a Complex Sound. A complex sound usually is made up of multiple sine waves oscillating at different frequencies.
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FIG.2
FIG.1
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