Blog What is Sound?

The scientific explanation would be something like:

Changes in atmospheric pressure which causes air molecules to move.

Our ears register this molecular movement or vibration, and our brains interpret it as "sound".

"Sound waves decrease over distance due to a loss of energy."

The one thing we're not going to do is math. As a direct quote from Tony, "I suck at math, so anything that involves math, I'll give you like really basic stuff and I'll be like, that's about as far as we're going with math, because me and math we don't get along!" — and he'll tell you that math isn't really required for this kind of thing, anyway! Besides, different factors determine the size and shape of the sound wave.

For example: when an object is dropped into a body of water, the water is displaced in waves that radiate outwards from the source of impact, moving in an up and down pattern.

Louder sounds can travel farther than quiet sounds, for example, as the factors involved in creating the sounds can have an impact on the size of the sound waves and thus how far those sounds can travel.

Anatomy of a Wave

The picture above shows us both a Longitudinal Wave and a Transverse or Sine Wave (pronounced “sign”). This is essentially the ‘anatomy’ of a sine wave as far as our ears perceive it, and it is made up of four fundamental factors:

  • The Peak - This marks the highest point in the wave;
  • The Trough - This is the opposite of the peak, marking the lowest point in the wave;
  • Compression - This is what happens to the sound as is travels upwards towards the peak, and is where we can perceive a climbing in “pitch”; and
  • Rarefaction - This is what happens as the sound falls down into the trough, and we hear the opposite effect shown during compression, which is where the pitch 'drops' as the sound particles (the wave) becomes less compressed.

    • In the example shown above, the Longitudinal Wave shows the spread of sound particles as they are emitted from a speaker and are picked up by our ears, and it gives us a visual representation of the molecules within a sound wave as they undergo both compression and rarefaction. Once this wave hits our ears, it is perceived in the order of how the molecules arrive, thus we hear the particles (or wave) alternately at both its most compressed and dispersed states.

    The Transverse or Sine Wave provides an alternate or “side view” of this same phenomenon, and this is also a mechanical point-of-view as this is how sounds are displayed in our computer programs and on devices like oscilloscopes, etc.

    The term Hertz (Hz) is the unit of frequency that is most commonly used to measure sine waves and musical tones, and is defined as being “one cycle per second”. You will have likely heard the terms “kilohertz” or “megahertz” at some stage, and it is quite likely that this is what-and-why the term was being used.

    A “cycle” consists of a single Peak and single Trough, making up 1Hz. Therefore 1,000 cycles = 1kHz (1 kilohertz). We’ll touch on Hertz and frequency again shortly to provide some practical context for the terms.

    The Phase of a sound wave is basically “how far along a waveform is in its current cycle”. The scope of this course doesn’t require an in-depth study of the various aspect of an audio phase, but you can find some excellent further reading here. However, to provide a visual aid to support the above definition, please refer to the below graph (found at the same link):

    Amplitude – this will be defined in-depth shortly.

    When sound waves are combined, we get more complex waves: Phase Amplification - When two waves of equal amplitude and frequency are combined, we get a wave that is DOUBLE in amplitude.

    However, if we combine sound waves of equal amplitude and frequency but have opposite states of pressure (compression vs rarefaction) the waves can cancel each other out - Phase Cancellation. This may mean you might get a ‘weak’ or ‘thin’ sound, or no sound at all.

    This is more often seen when recording instruments, especially when using two microphones (for example, when recording a guitar or drums). When it comes to voiceover, however, it’s not likely to be something that you’d need to be too vigilant for, but that’s not to say that it cannot happen!

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