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Input TransducersInput Transducers
(Microphones)
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MicrophonesMicrophones
Transducers that convert sound waves into electrical signals
There are several different type of microphonesDynamicCondensingCarbon granule
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DynamicDynamic
The diaphragm is moved by changing sound pressure
This moves the coil, which causes current to flow as lines of flux from the magnet are cut
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DynamicDynamic
Advantages Rugged Inexpensive to manufactureTolerates extremely high sound
pressure levels Requires no power supply
DisadvantagesReduced high frequency performanceNeeds amplification
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CondensingCondensing
A pair of parallel metal plates separated by an insulator across which is stored an electrical charge
Q=CV Moving the plates will
change the voltage across them causing current to flow in or out of the capacitor through the resistor
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Charging the Condensing Mic
Charging the Condensing Mic
The microphone must have some means of charging the platesBattery Phantom poweringElectret
The majority of serious recording work is carried out with capacitor microphones
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CondensingCondensing
Advantages No coil and the diaphragm can be
made very thin (few microns thick) thus light weight and less inertia so better high frequency response.
Capacitor microphones can be made with virtually any response pattern.
Disadvantages More complex thus more expensive
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Carbon GranuleCarbon Granule
When acoustical pressure is exerted on the carbon granules, the granules are pressed closer together which decreases the measured resistance.
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Pickup PatternsPickup Patterns
Microphones can also be classified by their pick up patterns Omnidirectional UnidirectionalBidirectional
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OmnidirectionalOmnidirectional
Pickup of sound equally well within a 360 degree radius around the microphone element
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OmnidirectionalOmnidirectional
Advantages Doesn't have to held directly in front of
sound source to pick up adequate sound Gives a sense of the environment Is not affected by slight changes in mic-
to-source distance Provides a natural sound in rooms with
good acoustics Is less susceptible to handling noise and
noise created by wind or popping Is not subject to the proximity effect
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OmnidirectionalOmnidirectional
Disadvantages Difficult to use in noisy locations Susceptible to feedback in
locations where microphone is feeding a loudspeaker
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Unidirectional (Cardioid)Unidirectional (Cardioid)
Primary pickup of sound from one side of the microphone's element Wide angle cardioid Supercardioid Hypercardioid
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UnidirectionalUnidirectional
Advantages Discriminates against
unwanted sound Reduces danger of
feedback in locations where microphone is feeding a loudspeaker
Picks up very little or no background sounds
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UnidirectionalUnidirectional
Disadvantages May be subject to the proximity effect Must be set correctly to avoid sound
source being off-mic Less natural sound in rooms with good
acoustics Must take care to avoid covering ports More susceptible to wind, popping and
handling noises
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BidirectionalBidirectional
Optimum pickup of sound from two sides of the microphone elementAdvantage - can be used to
reduce number of mics in a circuit when two voices are involved in an interview or performing a voice-over
Disadvantage - no separate control over levels of talent, so they must maintain proper mic-to-source distance and remain on-mic
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Proximity EffectProximity Effect
The closer the sound source is to the microphone, the greater the emphasis on the bass frequencies in the sound
Many microphones are equipped with a bass roll-off switch to nullify the proximity effect
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Condenser Frequency Response
Condenser Frequency Response
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Dynamic Frequency Response
Dynamic Frequency Response
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ImpedanceImpedance
One important characteristic of a microphone is its output impedance
This is a measurement of the AC resistance looking back into the microphoneLow (50-1,000 ohms)High (5,000+ ohms)
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Low ImpedanceLow Impedance
Most microphones used in broadcast applications are wired for low-impedance circuits Low-impedance circuits
have three wire connectors: a shield and two other wires (hot and cold) to conduct the current
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Balanced SystemsBalanced Systems
Balanced lines are much less susceptible to RFI (Radio Frequency Interference) and the pickup of the other electrical noise and hum
In a balanced line, the shield of the cable is connected to ground, and the audio signal appears across the two inner wires which are not connected to ground
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Balanced SystemsBalanced Systems
Output signal is split into two opposite phasesPositive and Negative or Hot and ColdWhen returned to the same phase at the
amplifier input noise is cancelled.
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Phantom PoweringPhantom Powering
The standard power supply for microphones is 48v
DC power is supplied along the signal leads, which means no extra cables
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ConnectorsConnectors
Two types of connectors are commonly used with balanced systems
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High ImpedanceHigh Impedance
High-impedance circuits have two wire connectors: a shield and one inner wireUsed in budget systemsHigh impedance makes the signal more
susceptible to electromagnetic interference
Signal is affected by cable capacitance in long runs of cables
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FeedbackFeedback
Feedback occurs when the sound from the loudspeaker arrives at the microphone as loud or louder than the sound arriving directly from the original sound source (talker, singer, etc.)
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Microphones and Stereo Signals
Microphones and Stereo Signals
Coincident or XY pairRight hand microphone
picks up sound form left stage and visa a versa
No phase problems as minimal space between microphones
Sound source
Cardioid Microphones
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FinFin
Fin