Technology – Audio Technology
The conversion of sound waves into electrical signals opens up a wide range of possibilities for recording voice, music, and other sounds, and then storing, processing, and replaying them.
Sound waves are traveling vibrations in gases, liquids, or solids. Humans can generally perceive a range of some 16 to 20,000 hertz (cycles per second), although this varies according to age, hearing ability, and the volume of the sound.
Microphones
To convert sound into electrical signals, microphones are used. Microphones can be categorized largely based on their sound fidelity, frequency range, and applications for which they are used. Various methods can be used to transform sound into electrical impulses. Most microphones have a thin elastic membrane that is vibrated by sound waves.
In moving-coil microphones, the membrane transfers its motion to a coil within a magnetic field. This produces an alternating electrical current corresponding to the pattern of
the sound. The resulting electrical signals are then amplified, so that they can be recorded and further processed.
Storage
Today voice and music are usually recorded and stored digitally. To do this, electrical signals coming from the microphone are sampled several thousand times per second. The measured values are then coded and stored for later processing on a computer. Music can be stored in the form of MP3 files on a computer’s hard drive or other storage medium. The huge volume of data is reduced using various techniques.
For instance, only the components of the recording that humans can actually hear are stored. The compact disc (CD), on the other hand, is an optical storage medium. It consists of a plastic disc with a layer of aluminum and a transparent coating. The digitized sound signal is stored in a series of tiny indentations in the aluminum layer, laid down in spiral form around the disc.
Playback devices use the beam of a semiconductor laser to read the data from the disc. The original electrical signal can then be recreated from the digital data, amplified and transformed back into sound by speakers.
Speakers
Speakers create sound waves from electrical signals. A common type is the dynamic speaker, which uses an electrical coil suspended within a cup-shaped permanent magnet. The coil is connected to a membrane. When a pattern of electrical signals flows through the coil, the membrane vibrates in response to the signal, producing sound.
Larger membranes are better suited for emitting lower notes, while smaller membranes reproduce higher tones more effectively. Thus signals are routed to various sizes of speaker within a speaker box, depending on their frequency ranges.
RECORDING STUDIOS
In a recording studio, voices, music, and other sounds are recorded and processed for audio CDs, radio broadcasts, or movie sound-tracks. The facility may include a control room as well as the studio where the recordings are made. Soundproofing and other techniques are used to create excellent acoustic conditions.
With the help of multitrack recording devices or computer-based systems, several different sound sources can be recorded separately.
BASICS
SINE WAVES are perceived by the ear as “pure” tones. Increasing numbers of cycles per second (higher frequencies) produce a higher note.
Noises are made up of a mixture of tones, resulting in irregular sound waves.