Audio

Audio

Prepared By: MMPT

Source: Media College (mediacollege.com)

What is "Audio"?

O Audio means "of sound" or "of the

reproduction of sound". Specifically, it refers

to the range of frequencies detectable by

the human ear — approximately 20Hz to

20kHz.

O It's not a bad idea to memorize those

numbers — 20Hz is the lowest-pitched

(bassiest) sound we can hear, 20kHz is the

highest pitch we can hear.

What is "Audio"?

O Audio work involves the production, recording,

manipulation and reproduction of sound waves.

To understand audio you must have a grasp of

two things:

O Sound Waves: What they are, how they are

produced and how we hear them.

O Sound Equipment: What the different components

are, what they do, how to choose the correct

equipment and use it properly.

What is "Audio"?

O Fortunately it's not particularly difficult. Audio

theory is simpler than video theory and once you

understand the basic path from the sound source

through the sound equipment to the ear, it all

starts to make sense.

O Technical note: In physics, sound is a form of

energy known as acoustical energy.

The Field of Audio Work O 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: O Studio Sound Engineer

O Live Sound Engineer

O Musician

O Music Producer

O DJ

O Radio technician

O Film/Television Sound Recordist

O Field Sound Engineer

O Audio Editor

O Post-Production Audio Creator

The Field of Audio Work O 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.

O Speaking of video-making, it's important to recognize the importance of audio in film and video. A common mistake amongst amateurs is to concentrate only on the vision and assume that as long as the microphone is working the audio will be fine. However, satisfactory audio requires skill and effort. Sound is critical to the flow of the programme — indeed in many situations high quality sound is more important than high quality video.

The Field of Audio Work O Most jobs in audio production require some

sort of specialist skill set, whether it be

playing a drum kit or creating synthetic

sound effects. Before you get too carried

away with learning specific tasks, you should

make sure you have a general grounding in

the principles of sound. Once you have done

this homework you will be well placed to

begin specializing.

O The first thing to tackle is basic sound wave

theory...

How Sound Waves Work

Before you learn how

sound equipment works it's very

important to understand how

sound waves work. This knowledge will

form the foundation of everything you

do in the field of audio.


O Sound waves exist as variations of pressure

in a medium such as air.

O They are created by the vibration of an

object, which causes the air surrounding it

to vibrate.

O The vibrating air then causes the human

eardrum to vibrate, which the brain

interprets as sound.


O Sound waves travel through air in much the

same way as water waves travel through

water.

O In fact, since water waves are easy to see

and understand, they are often used as an

analogy to illustrate how sound waves

behave.

How Sound Waves Work O Sound waves can also be shown in a standard x vs

y graph, as shown here. This allows us to visualise

and work with waves from a mathematical point of

view. The resulting curves are known as the

"waveform" (i.e. the form of the wave.)


O The wave shown here represents a constant tone at

a set frequency. You will have heard this noise being

used as a test or identification signal. This "test

tone" creates a nice smooth wave which is ideal for

technical purposes. Other sounds create far more

erratic waves.


O Note that a waveform graph is two-dimensional

but in the real world sound waves are three-

dimensional.

O The graph indicates a wave traveling along a

path from left to right, but real sound waves

travel in an expanding sphere from the source.

O However the 2-dimensional model works fairly

well when thinking about how sound travels from

one place to another.


O The next thing to consider is what the graph

represents; that is, what it means when the

wave hits a high or low point.

O The following explanation is a simplified way

of looking at how sound waves work and

how they are represented as a waveform.

Don't take it too literally — treat it as a useful

way to visualize what's going on.


O In an electronic signal, high values represent high

positive voltage. When this signal is converted to

a sound wave, you can think of high values as

representing areas of increased air pressure.

O When the waveform hits a high point, this

corresponds to molecules of air being packed

together densely.

O When the wave hits a low point the air molecules

are spread more thinly.

How Sound Waves Work In the diagram below, the black dots represent air molecules. As the loudspeaker vibrates, it causes the surrounding molecules to vibrate in a particular pattern represented by the waveform. The vibrating air then causes the listener's eardrum to vibrate in the same pattern. Voilà — Sound!

Variations in Air Pressure and Corresponding Waveform


O Note that air molecules do not actually travel

from the loudspeaker to the ear (that would

be wind).

O 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.


O Now here's the thing:

O All audio work is about manipulating sound

waves. The end result of your work is this

series of high and low pressure zones.

O That's why it's so important to understand

how they work - they are the "material" of your

art.

Sound Wave Properties


All waves have certain

properties. The three most

important ones for audio

work are shown here:


O Wavelength: The distance between any point

on a wave and the equivalent point on the

next phase. Literally, the length of the wave.

Sound Wave Properties O Amplitude: The strength or power of a wave signal.

The "height" of a wave when viewed as a graph.

O Higher amplitudes are interpreted as a higher

volume, hence the name "amplifier" for a device

that increases amplitude.

Sound Wave Properties O Frequency: The number of times the wavelength

occurs in one second. Measured in kilohertz (Khz), or

cycles per second. The faster the sound source

vibrates, the higher the frequency.

O Higher frequencies are interpreted as a higher pitch.

For example, when you sing in a high-pitched voice

you are forcing your vocal chords to vibrate quickly.

How Sound Waves Interact with Each

Other

How Sound Waves Interact with Each Other

When different waves collide (e.g.

sound from different sources) they

interfere with each other. This is

called, unsurprisingly, wave

interference.


O Phasing

O The following table illustrates how sound waves (or

any other waves) interfere with each other depending

on their phase relationship:


O Sound waves which are exactly in phase add

together to produce a stronger wave.

O Sound waves which are exactly inverted, or 180

degrees out of phase, cancel each other out and

produce silence. This is how many noise-

cancellation devices work.

O Sound waves which have varying phase

relationships produce differing sound effects.

Sound Systems

Sound Systems O Working with audio means working with

sound systems. Naturally, the range of

systems available for different applications

is enormous.

O However, all electronic audio systems are

based around one very simple concept:

O To take sound waves, convert them into an

electric current and manipulate them as desired,

then convert them back into sound waves.

Sound Systems O A very simple sound system is shown in the

diagram below. It is made up of two types of

component:

O Transducer - A device which converts energy from

one form into another. The two types of transducers

we will deal with are microphones (which convert

acoustical energy into electrical energy) and

speakers (which convert electrical energy into

acoustical energy).

O Amplifier - A device which takes a signal and

increases its power (i.e. it increases the amplitude).

Sound Systems

O The process begins with a sound source (such as a human

voice), which creates waves of sound (acoustical energy).

O These waves are detected by a transducer (microphone),

which converts them to electrical energy.

O The electrical signal from the microphone is very weak, and

must be fed to an amplifier before anything serious can be

done with it.

O The loudspeaker converts the electrical signal back into

sound waves, which are heard by human ears.

Sound Systems O The next diagram shows a slightly more elaborate

system, which includes:

O Signal processors - devices and software which allow

the manipulation of the signal in various ways. The

most common processors are tonal adjusters such

as bass and treble controls.

O Record and playback section - devices which convert

a signal to a storage format for later reproduction.

Recorders are available in many different forms,

including magnetic tape, optical CD, computer hard

drive, etc.

Sound Systems

O The audio signal from the transducer (microphone) is

passed through one or more processing units, which

prepare it for recording (or directly for amplification).

O The signal is fed to a recording device for storage.

O The stored signal is played back and fed to more

processors.

O The signal is amplified and fed to a loudspeaker.

Sound Systems O The 3-part audio model

O One simple way of visualising any audio system is by dividing

it up into three sections: the source(s), processor(s) and

output(s).

O The source is where the electronic audio signal is generated.

This could be a "live" source such as a microphone or

electric musical instrument, or a "playback" source such as

a tape deck, CD, etc.

O The processing section is where the signal is manipulated.

For our purposes, we will include the amplifiers in this

section.

O The output section is where the signal is converted into

sound waves (by loudspeakers), so that it can be heard by

humans.

Sound Systems This portable stereo is a good example of a simple

system.

Sound Systems O Sources: There are three sources - two tape

machines and one radio aerial (technically the

radio source is actually at the radio station).

O Processors: Includes a graphic equalizer, left/right

stereo balance, and amplifiers.

O Outputs: There are two speaker cabinets (one at

each end), each containing two speakers. Note that

there are also two alternative outputs: A

headphone socket (which drives the small

speakers inside a headphone set) and twin "line

out" sockets (which supply a feed for an external

audio system).

Sound Systems O Now imagine a multi-kilowatt sound system

used for stadium concerts. Although this is

a complex system, at it's heart are the same

three sections: Sources (microphones,

instruments, etc.), processors and

speakers.

O Whatever the scale of the project, the same

underlying principles of sound reproduction

apply.

END

(40/40)

Prepared By: MMPT

Source: Media College (mediacollege.com)

Audio

Technology

o audio work

o sound equipment

field of audio work

sound source

principles of sound

bassiest sound

audio production

audio theory