Sound Theory
Sound Is an vibration in an elastic medium
such as air and water. It is generated by vibrated bodies in the form of waves
of compression and rarefaction in the air. Waveform is a curve showing the
shape of a an audio wave at a given time.
Wavelenght is the distance between waves.
A sound
wave is the pattern of disturbance caused by the movement of energy
traveling through a medium (such as air, water, or any other liquid or solid
matter) as it propagates away from the source of the sound.
Response:
We generally measure sound in terms of
pressure level or decibel (dB).
Amplitude is a measurement for change in
atmospheric pressure cause by sound waves.
Frequency – Represents the number of times that a repeated
event occurs per unit of time.
Hz and khz – Are the units for measuring
frequency.
Basics of Sound Recording?
To record a sound you would need a
microphone and a computer of some sort.
There are two types of microphones.
Condenser and Dynamic.
Mono – stereo – Mono usually represents one
audio channel, stereo is dual channel.
Digital audio – Digital audio signals are
encoded in digital form.
Analogue distortion – Analogue distortion
can be cause by multiple factors. Electrical interference, by amplyfing the
sound… The length of the cable that the audio is being transferred by.
File formats – wav, mp4, aiff, aac, atrac…
The dynamic
(moving-coil) microphone
operates by electromagnetic induction to generate an output signal voltage . It
is like a miniature loudspeaker working in reverse. The diaphragm is attached
to a coil of fine wire. The coil is mounted in the air gap of the magnet such
that it is free to move back and forth within the gap. When the sound wave
strikes the diaphragm, the diaphragm vibrates in response. As the coil moves
through the lines of magnetic force in the gap, a small electrical current is
induced in the wire. The magnitude and direction of that current is directly
related to the motion of the coil, and the current then is an electrical
representation of the sound wave.
The other major microphone type is the condenser. The diaphragm of a
condenser microphone is a very thin plastic film, coated on one side with gold
or nickel, and mounted very close to a conductive stationary back plate. A
polarizing voltage is applied to the diaphragm by an external power supply (battery
or phantom power ) or by the charge on an electret material in the diaphragm or
on the backplate charging it with a fixed static voltage. The diaphragm and back plate, separated by a small volume of
air, form an electrical component called a capacitor
(or condenser). The capacitance between these two plates varies as the freely
suspended diaphragm is displaced by the sound wave. When the diaphragm vibrates
in response to a sound, it moves closer to and farther away from the back
plate. As it does so, the electrical charge that it induces in the back plate
changes proportionally. The fluctuating voltage on the back plate is therefore
an electrical representation of the diaphragm motion.
You can also produce sound and music digitally with computer software.
Define Analogue/Digital Sound:
An analog recording is one where a property or
characteristic of a physical recording medium is made to vary in a manner
analogous to the variations in air pressure of the original sound.
A digital recording is produced by converting
the physical properties of the original sound into a sequence of numbers, which
can then be stored and read back for reproduction.
Two
prominent differences in functionality are the bandwidth and the signal-to-noise ratio (S/N); however, both
digital and analog systems have inherent strengths and weaknesses.
Advantages
of both:
Advantages
of Analogue
Once recorded,
audio is stored/archived.
Warm and natural
sound.
Theoretically
better audio bandwidth (this is arguable).
Tried and tested
format.
Editing
limitations discourage constant tinkering and procrastination.
Advantages of Digital:
Better sound for
cheaper equipment.
Potential for
very low distortion and noise/hiss.
Variety of
recorder options (tape, optical, hard disc, RAM etc).
Non-linear
operation (random access).
You can access
any part of the recording almost immediately.
Massive range of
editing and processing tools.
Non destructive
editing (you can make copies of data and undo decisions).
You can clone
data.
Audio can be
transmitted over networks.
Which
application are suitable for interactive media products?
We can intergrate
sound into multimedia:
Websites
DVDs
Games
Videos etc.
Why is sound important?
Sound it important for a couple of
reasons.
We use sound for
signaling
and communication. When a film maker makes a video, he needs to communicate
with the audience not just with visuals, but with sound as well. Sound can
cause us to feel certain emotions and connect with what we are watching or
listening.
