Audio
-
Upload
may-talandron -
Category
Technology
-
view
195 -
download
0
Transcript of 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.
How Sound Waves Work
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.
How Sound Waves Work
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.)
How Sound Waves Work
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.
How Sound Waves Work
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.
How Sound Waves Work
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.
How Sound Waves Work
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
How Sound Waves Work
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.
How Sound Waves Work
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
Sound Wave Properties
All waves have certain
properties. The three most
important ones for audio
work are shown here:
Sound Wave Properties
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.
How Sound Waves Interact with Each Other
O Phasing
O The following table illustrates how sound waves (or
any other waves) interfere with each other depending
on their phase relationship:
How Sound Waves Interact with Each Other
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)