Is there a difference between sound and audio? Aren't they the same thing?

Most people think of sound and audio being the same thing and for the average person that is ok, but as an audio technician you need to know what this difference is. Read on to find out more.

Sound is a type of energy made by vibrations. When an object vibrates (including vocal cords), it causes movement in surrounding air molecules. These molecules bump into the molecules close to them, causing them to vibrate as well. This makes them bump into more nearby air molecules. 

There is a progression of collisions that pass through the air as a sound wave. What the sound wave will sound like when it reaches the ear depends on a number of things such as the medium it travels through and the strength of the initial vibration. 

When the molecules are close together they create a high pressure and when there are less molecules clumped together it creates a low pressure. In the image (right) we can see how this translates into the image that we commonly know as a sound wave.

Note that air molecules do not actually travel from the loudspeaker to the ear (that would be wind). Each individual molecule only moves a small distance as it vibrates, but it causes the adjacent molecules to vibrate in a rippling effect all the way to the ear.

Activity

Watch the video (right) to help your understanding of what sound is.

There are some properties that make up sound that we need to look at further. Three ofthese we will be looking at today are:

• Frequency

• Wavelength

• Amplitude

Frequency, sometimes referred to as pitch, is the number of times per second that a sound pressure wave repeats itself. A drum beat has a much lower frequency than a whistle, and a bullfrog call has a lower frequency than a cricket. The lower the frequency, the fewer the oscillations. 

A wavelength is the distance between any point on a wave and the equivalent point on the next phase. Literally, the length of the wave. 

Watch the video (left) to summarise these three terms.

Audio means "of sound" or "of the reproduction of sound". It is electrical energy. All audio work is about manipulating sound waves. 

Audio specifically refers to the range of frequencies detectable by the human ear — approximately 20 Hertz to 20 Kilohertz.

➢    Hertz (Hz) = The unit of frequency equal to one cycle per second

➢    Kilohertz (kHz) = The measure of frequency equal to one thousand cycles per second

20Hz is the lowest-pitched sound we can hear, 20kHz is the highest pitch we can hear.

When different waves collide (e.g. sound from different sources) they interfere with each other. This is called, unsurprisingly, wave interference.

The image (left) illustrates how sound waves interfere with each other depending on their phase relationship.

Summary:

• Sound waves which are exactly in phase add together to produce a stronger wave.

• Sound waves which are exactly inverted, or 180 degrees out of phase, cancel each other out and produce silence. This is called Phase Cancellation. This is how many noise-cancellation devices work.

• Sound waves which have varying phase relationships produce differing sound effects.

The field of audio is vast, with many areas of specialty. Hobbyists use audio for all sorts of things, and audio professionals can be found in a huge range of vocations. Some common areas of audio work include:

• Studio Sound Engineer

• Live Sound Engineer

• Musician

• Music Producer

• DJ

• Radio Technician

• Film/Television Sound Recordist

• Field Sound Engineer

• Audio Editor

• Post-Production Audio Creator

In addition, many other professions require a level of audio proficiency. For example, video camera operators should know enough about audio to be able to record good quality sound with their pictures.

Most jobs in audio production require some sort of specialist skill set, whether it be mixing up a drum kit or creating synthetic sound effects. 

Collect a hard copy of the sheet (left) and define the first three terms based on your understanding from this lesson. You will complete the remainder of the terms next lesson.