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Fundamentals of Audio
Production
Chapter Six:
Recording, Storing, and Playback
of Sound
Fundamentals of Audio
Production. Chapter 6.
1
Mechanical storage
• The phonograph – cylinder recorder/player
developed by Thomas Edison.
Fundamentals of Audio
Production. Chapter 6.
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Mechanical storage
• Gramophone – Emil Berliner’s disk-based
mechanical recorder
Fundamentals of Audio
Production. Chapter 6.
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Mechanical storage
• By “shouting into the funnel,” a diaphragm
at the small end would vibrate
• A stylus attached to the diaphragm would
vibrate and cut a groove into the cylinder
or disk
• On playback, the stylus would track
through the groove, causing vibrations in
the diaphragm, which echoed through the
funnel
Fundamentals of Audio
Production. Chapter 6.
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Mechanical storage
• Modern record cutting lathes use
electromagnetic heads to convert audio
current into physical vibrations
• The electromagnets respond to audio
current by alternatively pushing/pulling the
stylus
• The vibrating stylus is heated to easily cut
a groove in the vinyl disk
Fundamentals of Audio
Production. Chapter 6.
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Mechanical storage
Fundamentals of Audio
Production. Chapter 6.
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Mechanical storage
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Production. Chapter 6.
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Mechanical storage
• Modern phonographs use electromagnetic
transducers called cartridges
• Cartridges convert potential physical
energy, which is stored in the grooves of
the recording, into electrical energy
• The stylus follows the undulating groove
• Movements of the stylus, vibrate a small
magnet/coil mechanism
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Production. Chapter 6.
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Mechanical storage
Fundamentals of Audio
Production. Chapter 6.
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Magnetic tape recording
• Magnetic recording heads are transducers
that convert electrical energy into
magnetic energy
• Recording heads are electromagnets
• Audio current creates an alternating
magnetic field
• The magnetic field is focused at the “gap”
in the record head
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Production. Chapter 6.
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Magnetic tape recording
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Production. Chapter 6.
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Magnetic tape recording
• The fluctuations in the magnetic field are
stored on tape by re-arranging the
magnetic polarity of the “metal” surface of
the tape
• The tape surface is made from powdered
metals, like FeO2, or iron oxide (rust)
• The metals are attached to a plastic
backing with binder (glue)
Fundamentals of Audio
Production. Chapter 6.
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Magnetic tape recording
• Playback heads are constructed in a
nearly identical manner
• During playback, a current is induced to
flow in the coil of the head by the magnetic
charges of the tape surface
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Production. Chapter 6.
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Analog tape recording
• The paths on the tape where audio is
recorded are called “tracks”
• The inputs on the recorder are called
“channels”
• Stereo formats are two channel, but may
be two or four tracks
Fundamentals of Audio
Production. Chapter 6.
14
Analog tape recording
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Production. Chapter 6.
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Analog tape recording
• Tape width and track spacing affect cross
talk between tracks
• Tape speed affects fidelity
– Higher tape speeds produce greater signal-tonoise ratios
– Higher tape speeds produce wider frequency
responses
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Production. Chapter 6.
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Analog tape recording
The Philips compact cassette
and track configuration
Fundamentals of Audio
Production. Chapter 6.
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Analog tape recording
Reel to reel
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Production. Chapter 6.
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Analog tape recording
Reel to reel
Fundamentals of Audio
Production. Chapter 6.
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Analog tape recording
Cartridges
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Production. Chapter 6.
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Analog tape recording
• Commonalities across tape platforms
– Head arrangements
• First erase, second record, and last reproduce
– Capstan and pinch roller squeeze together
and pull the tape
Fundamentals of Audio
Production. Chapter 6.
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Analog tape recording
Fundamentals of Audio
Production. Chapter 6.
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Digital tape recording
• Digital audio tape stores binary data
(on/off) represented by short bursts of
electrical current
• Stationary head systems (DASH) use reelto-reel tape transports
• DAT systems use helical scanning rotating
head
Fundamentals of Audio
Production. Chapter 6.
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Digital tape recording
Fundamentals of Audio
Production. Chapter 6.
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Optical storage
• Electrical energy is converted into light
energy by a LASER
• The LASER burns microscopic pits into
the surface of a glass disk
• Binary data (on/off) triggers the LASER
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Production. Chapter 6.
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Optical storage
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Production. Chapter 6.
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Optical storage
• Compact disks are read by a LASER
• Light is refracted into a photoreceptor by
“bumps” on the surface of the disk
• Each pulse of light is equal to an “on” state
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Production. Chapter 6.
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Optical storage
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Production. Chapter 6.
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Optical storage
• The pits made by the LASER are .5
microns wide and up to 3.5 microns in
length
• How big is that?
• http://www.cellsalive.com/howbig.htm
• Data is stored redundantly on the disk to
avoid destruction or obliteration by dirt
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Production. Chapter 6.
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Solid state storage
• “Flash” memory is constructed from layers
of layers of conductive and non-conductive
materials
• The layers function as transistors
• Current is passed through the device’s
thousands of transistors
• If it passes through, it represents an “on”
in binary code
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Production. Chapter 6.
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Solid state storage
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Production. Chapter 6.
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Solid state storage
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Production. Chapter 6.
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Discussion
• What are the relative advantages and
disadvantages of
– Mechanical
– Magnetic
– Optical
– Solid state
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Production. Chapter 6.
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