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Audio

Recording and playing sound
by

David Mancuso

on 10 December 2012

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Transcript of Audio

Audio Technology of Sound There are two main types of audio information storage media

Analog, which comes in both mechanical and magnetic varieties,

And digital Audio Technologies Most commonly known for its use in cassette tapes

Works on a similar analog principal of data storage as the mechanical method

A large variety of proprietary tapes and players have come out over the years Popularized by the CD

More commonly used today as files on nearly any personal computing device

Most recent and versatile format

Works in an entirely different fashion in terms of storage than the analog methods What is sound? Sound is a sequence of pressure waves which transmit through a medium Mechanical Magnetic Digital Most commonly known for its use in record players

This was the first method of audio information storage invented

Technically any solid could be used to store this type of data Methods of Audio Storage How does it work? Audible compression waves hit a flexible diaphragm causing a needle to scratch into a rotating disc shaped material to match this oscillating wave form

Playback is a reversal of this process
A needle is drawn through the created grooves

Variations in the movement of the needle are transmitted by electrical signals to a flexible diaphragm which vibrates the air to recreate the initial wave form This is a close up of the grooves. These are a physical representation of the compression waves we hear as sound. Mechanical Audio Tech
Over Time 1877 Phonograph Cylinder
Thomas Edison 1895 Grammaphone Record 1948 Vinyl Record How does it work? Magnetic tape runs across an electromagnet which acts in a similar way to the previously mentioned needle by aligning the magnetic field in the tape to the vibrating air wave form being applied to the flexible diaphragm

Playback is also similar to mechanical analog audio in that the playhead magnet detects the wave form present in the magnetic field as a mechanical needle would trace the groove

The playhead sends corresponding electrical signals which vibrate another flexible diaphragm to recreate the compression waves This is a computer model of a magnetically stored audio sample (below) with the translated audio signal (above). Magnetic Audio Tech
Over Time 1935 Magnetophon 1962-1965 4-track/8-track 1968 Compact Cassette How does it work? Vibrations of the flexible diaphragm are not transmitted directly as a wave form like the previous methods.

Instead they are “sampled”. This means that the digital storage device takes snapshots of the incoming compression waves.

The snapshots or "slices" separate the wave form into discrete pieces ranging from a few thousand to hundreds of thousands of slices per second depending on the
quality desired Number of slices is the sampling rate and is measured in hertz or (Hz) the common unit for a frequency of cycles


Hz increase = the amount of slices increase, and the wave form becomes truer to its original form and thus has greater quality. Is that all? No... Digital audio comes in a variety of formats with varieties of compression

Compression- a method of reducing digital file size by eliminating redundant or unnecessary data

Digital audio compression can reduce aspects of the file such as sampling rate or frequency range

Some file types are lossy which lose quality upon compression for economical file size
MP3
AIFF
WMA

Others are lossless which retain the original recorded quality but with a much larger file size
FLAC
ALAC
M4A Digital Audio Tech
Over Time 1972 Digital audio tape 1982 Compact disc 2001 iPod
Full transcript