Download Multimedia Systems - University of Sussex

Input Transducers
(Microphones)
1
Microphones
 Transducers
that convert sound waves
into electrical signals
 There are several different type of
microphones
Dynamic
Condensing
Carbon
granule
2
Dynamic
 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
3
Dynamic
 Advantages
Rugged
Inexpensive
to manufacture
Tolerates extremely high sound
pressure levels
Requires no power supply
 Disadvantages
Reduced
high frequency performance
Needs amplification
4
Condensing

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
5
Charging the Condensing Mic
 The
microphone must have some
means of charging the plates
Battery
Phantom
powering
Electret
 The
majority of serious recording work
is carried out with capacitor
microphones
6
Condensing
 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
7
Carbon Granule
 When
acoustical
pressure is exerted on
the carbon granules,
the granules are
pressed closer
together which
decreases the
measured resistance.
8
Pickup Patterns
 Microphones
can also be classified by
their pick up patterns
Omnidirectional
Unidirectional
Bidirectional
9
Omnidirectional
 Pickup
of sound equally well
within a 360 degree radius
around the microphone element
10
Omnidirectional
 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 micto-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
11
Omnidirectional
 Disadvantages
Difficult
to use in noisy locations
Susceptible to feedback in
locations where microphone is
feeding a loudspeaker
12
Unidirectional (Cardioid)
 Primary
pickup of sound from one
side of the microphone's element
Wide
angle cardioid
Supercardioid
Hypercardioid
13
Unidirectional
 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
14
Unidirectional
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
15
Bidirectional

Optimum pickup of sound
from two sides of the
microphone element
 Advantage
- 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
16
Proximity 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
17
Condenser Frequency Response
18
Dynamic Frequency Response
19
Impedance
 One
important characteristic of a
microphone is its output impedance
 This is a measurement of the AC
resistance looking back into the
microphone
Low
(50-1,000 ohms)
High (5,000+ ohms)
20
Low Impedance
 Most
microphones
used in broadcast
applications are
wired for lowimpedance circuits
Low-impedance
circuits
have three wire
connectors: a shield and
two other wires (hot and
cold) to conduct the
current
21
Balanced 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
22
Balanced Systems
 Output
signal is split into two opposite
phases
Positive
and Negative or Hot and Cold
When returned to the same phase at the
amplifier input noise is cancelled.
23
Phantom Powering
 The
standard power supply for
microphones is 48v
 DC power is supplied along the signal
leads, which means no extra cables
24
Connectors
 Two
types of connectors are commonly
used with balanced systems
25
High Impedance
 High-impedance
circuits have two
wire connectors: a shield and one
inner wire
Used
in budget systems
High impedance makes the signal more
susceptible to electromagnetic
interference
Signal is affected by cable capacitance in
long runs of cables
26
Feedback
 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.)
27
Microphones and Stereo Signals
 Coincident
Right
or XY pair
hand microphone
picks up sound form left
stage and visa a versa
No phase problems as
minimal space between
microphones
Sound source
Cardioid Microphones
28
Fin
Fin
29