Transcript Fundamentals of Audio Production

Fundamentals of Audio
Production
Chapter Two:
Capturing Sound Electronically
Fundamentals of Audio
Production. Chapter 2
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Converting Sound into Electricity
• Because sound is essentially a vibration,
vibrations must be converted into
electricity.
• Sound is converted into electricity using
transducers.
• Transducers convert one form of energy
into another form.
• In this case: physical energy into electrical
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Production. Chapter 2
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Understanding electricity
• Electrical current flow is simply electrons
in motion in a conductor.
• Electrons are negatively (-) charged
subatomic particles in all substances.
• Electrons orbit the nucleus of the atom.
• Electrons are held in orbit by the electrical
attraction of positively (+) charged protons
in the nucleus.
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Production. Chapter 2
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Understanding electricity
Because particles with similar electrical charges repel one another, electrons
forced to move into the orbit of adjacent atoms will dislodge electrons there,
where they will move to the next adjacent atom and dislodge electrons
there, and so on…
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Production. Chapter 2
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Understanding electricity
• Substances that have more electrons than
protons, have “free electrons”
• Free electrons are easily dislodged from
their orbits
• Substances with free electrons are called
“conductors.”
• The more free electrons in the substance,
the better conductor it is – the more easily
current will flow.
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Production. Chapter 2
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Understanding electricity
• Because electrons do have some mass,
there is an opposition for them to leave
their orbits.
• This reluctance to move is called
“resistance.”
• Good conductors, with more free
electrons, have lower resistance.
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Production. Chapter 2
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Understanding electricity
• When the electrons flow only in one
direction, the current flow is called “direct
current,” or DC.
• When the electrons flow in both directions,
the current flow is called “alternating
current,” or AC.
• Once sound is converted into current flow,
audio signals are AC.
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Production. Chapter 2
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Transducers
• Transducers are used to convert vibrating
air molecules into electrical current flow.
• Transducers use principles of
electromagnetism, electrostatics, and
physical characteristics of some
substances to convert vibrations into
electricity.
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Production. Chapter 2
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Transducers
• Common types of transducers
– Dynamic
– Condenser (electrostatic)
– Ribbon
– Piezoelectric
– Carbon
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Production. Chapter 2
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Dynamic transducer
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Production. Chapter 2
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Dynamic transducer
• Sound pressure waves cause the
diaphragm to vibrate
• The vibrations in the diaphragm are
transferred to the coil
• As the coil moves within the magnetic field
of the permanent magnet, current is
induced to flow in the coil
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Production. Chapter 2
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Dynamic transducer
Positive air pressure
creates positive voltage
Negative air pressure
creates negative voltage
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Production. Chapter 2
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Dynamic transducer
• Dynamic transducers are physically
rugged and will withstand rough handling
and field use
• Dynamic transducers are inexpensive to
manufacture
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Production. Chapter 2
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Ribbon transducer
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Production. Chapter 2
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Ribbon transducer
• A thin strip of corrugated metal foil is
suspended under tension within a strong
magnetic field
• Sound pressure waves cause the ribbon to
flex within the magnetic field
• The movements of the ribbon within the
magnetic field induced current to flow
along the ribbon
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Production. Chapter 2
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Ribbon transducer
• Ribbon transducers are delicate and will
not withstand rough handling
• High sound pressure levels or bursts of
wind will cause the ribbon to permanently
sag
• Ribbons are not well-suited to field use
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Condenser transducers
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Production. Chapter 2
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Condenser transducers
• Two plates are placed in close proximity,
but separated by a thin air gap
– One plate is the diaphragm
– One plate is called the back plate
• Voltage (phantom power) is applied to one
of the plates
• Sound pressure waves cause the
diaphragm to vibrate
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Production. Chapter 2
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Condenser transducers
As positive air pressure moves the
plates closer together, more current will
flow away from the back plate. The
electrons on the diaphragm repel the
electrons on the back plate.
As negative air pressure allows the
plates to rebound, less current will flow
away from the back plate.
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Production. Chapter 2
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Condenser transducers
• Condenser transducers require a power
supply
– May be in the mixing console
– May be from a battery
– May be from an external power supply
• Condenser transducers are capable of
wide flat frequency response.
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Production. Chapter 2
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Carbon transducers
Piston
Carbon
Telephone handset carbon transducer
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Production. Chapter 2
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Carbon transducers
• A receptacle is filled with carbon, which
will conduct current
• Air pressure waves cause the diaphragm
to vibrate
• The diaphragm is attached to a piston,
which compresses the carbon during the
positive phase of the audio wave
• As the carbon is compressed the current
flow increases
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Carbon transducers
• Carbon transducers tend to reproduce
limited bandwidth
• Carbon transducers are not commonly
used for high fidelity audio, but are still
used in voice circuits (telephones,
intercoms, etc.)
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Piezoelectric transducers
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Production. Chapter 2
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Piezoelectric transducers
• Certain mineral crystals will generate a
current when stressed
• Sound pressure waves push the
diaphragm which in turn causes the crystal
to flex
• The vibrations in the crystal induce current
flow
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Piezoelectric transducers
• Piezoelectric
transducers tend to
have poor bandwidth
• Crystal transducers
are used in some
inexpensive
microphones
• The Shure™ “Green
Bullet” is a popular
crystal microphone for
harmonica
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Production. Chapter 2
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