Unit 63 - Task 1

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.