Wk3 Flashcards
Polar Patterns
The graph/range of frequency sensitivity on a microphone type
Cardioid Pattern
Shaped like a “heart”
* Good at rear and side rejection
* Good in small rooms to
decrease reflection
* Good to reject signal from stage
monitors (reduce feedback)
Omnidirectional Pattern
Equally sensitive in all directions
* Good at capturing sound from a
wide area.
* Does not localise sound, does not discriminate in what it picks up
* Good for lapels – is not as affected
by position as directional patterns
Directional Response: Axis and Off-Axis
The degree of distance from the mic’s focus point/s, if it has them
Say if recording dialogue, really only want that dialogue as clear and specific as possible, so 0°
Frequency Response
Describes how sensitive a microphone is to different frequencies.
* Amplitude change over frequency spectrum.
Almost all microphones have an uneven frequency response, that is they capture
certain frequencies better or worse than others.
This is often deliberate, with mics being deliberately “voiced” for certain applications.
Proximity Effect
Boost in bass frequencies created when recording sources in close proximity to cardioid
microphones.
(occurs for both dynamic and condenser microphones)
It is often used for effect. A vocalist can get a deep, warm tone by singing very close to the mic. Often used by “crooners” and radio DJs.
Can be used effectively to cut feedback in a sound reinforcement situation
Plosives
Plosive describes the rush of air inherent in pronouncing hard consonants like “P”, “B”, “K” and “T” etc.
These plosives often cause distortion or peaks in signal (popping sounds) at the microphone which become a
problem
How could you prevent plosives?
Place the mic slightly off-axis to reduce plosives.
A “pop” filter made of fabric, metal mesh, or even foam should be placed between the vocalist and microphone
(also protects the diaphragm which is delicate thin sliver of gold)
Dynamic Mics
Work on electromagnetic induction principle (electrons in a wire are induced to move (electrical current) due to being
passed through a magnetic field)
Moving coil mics and ribbon mics are both examples of dynamic microph
Will pick up less of room than condenser
Moving Coil Mic
(Dynamic) Has the voice coil thingy that transmits down the magnet
Moving coil microphones are often preferred for use on stage, because they are quite sturdy and do not require external power.
Ribbon Mic
(Dynamic) Use the same principle as moving coil dynamics, except instead of a diaphragm (often made of non-conductive material) being attached to a voice coil,
the diaphragm itself is made of a conductive material and suspended within the magnetic field
Much more fragile and more expensive than moving coil dynamics, but are known to have a very smooth, detailed sound
Condenser Microphone
Must be powered from either:
* Phantom power provided by audio
interface, preamp, or mixing console
(select +48V).
* External power source (older mics)
*Vacuum tubes
* Diaphragm construction vs coil (dynamic
mic) offers a more sensitive/responsive mic
* Higher sensitivity and lower noise than
dynamic mics.
Capacitance Variation
A condenser microphone operates based on the principle of capacitance variation due to changes in distance between two charged plates caused by sound pressure.
* Capacitance is a measure of the ability of a system to store electrical charge.
* A capacitor is an electronic component that stores energy in the form of an electrostatic field.
As the distance between the plates changes, the capacitance of the system changes accordingly
The backplate is typically permanently charged with a constant voltage (usually supplied by a battery or phantom power), while the diaphragm is a thin membrane positioned in front of the
backplate.
The variation in capacitance results in a corresponding variation in the electrical voltage across the plates. The microphone’s circuitry then converts this voltage variation into an electrical
signal.
Large Diaphragm
(Condenser) Most large-diaphragm mics are side-addressed
* Good for vocals – reduces the proximity effect
* Good to capture lower frequencies
* Large-diaphragms tend to have a better signal-to-noise ratio because they capture more acoustical information than a small-diaphragm
Small diaphragm
Excellent transient and high-frequency response
Consistent polar pattern/sensitivity across
frequency range
Small-diaphragm “pencil” mics are front-
addressed
Many have switches for dB and roll-off
This is good for adjusting to sound sources and environments.
Signal-to-noise ratio
The intended signal/sound versus the unwanted noise being picked up
How do dynamic mics work
Acoustic pressure wave passes through the diaphragm, hits the voice coil then gets sent down the magnet
What does the Pad switch do? (Condense mic)
Reduces amplitude (dB) sensitivity
Use this in loud recording environments to prevent distortion
What does the Roll Off switch do? (Condense mic)
Adjusts frequency sensitivity
Low-cut filter.
Use this to remove unwanted low frequencies
Stereophony
Stereo. Reproduces or creates an illusion of multi-directional audible
perspective.
Two or more independent audio channels deliver sound to listeners, creating a sense of depth, spaciousness, and localization of sound sources
How do we create stereo sound?
- Stereo Recording Techniques
- Stereo Mixing (panning)
Stereophony
Spatial or binaural localization
The capability of two ears to localize a sound source within an acoustic space (tell the direction of where sound is coming from)
This effect is the result of three acoustic cues that are received by the ears:
* Interaural intensity differences
* Interaural arrival-time differences
* The effects of the pinnae (outer ears)
Interaural
Of or relating to sound reception and perception by each ear considered
separately
- Interaural intensity differences
- Interaural arrival-time differences
- The effects of the pinnae (outer ears)
A) Interaural intensity differences: Helps us locate middle to high-frequency sounds.
B) Interaural arrival-time differences: Helps us locate low-frequency sounds.
C) The pinnae (outer ears) help us determine if a sound originates from front, behind, or below
XY Mic Placement
Coincident Pair (capsules near touching)
* Capsules at 90º or 120º
* Both microphones must use cardioid pattern (use same make/model)
* There will be very little time delay between the two mics, as the sound source will reach both mics simultaneously.
* Good for minimizing phase cancellations
* Does not capture as much of the stereo image as a spaced pair (AB)
* XY using bi-directional or figure 8 pattern is a Blumlein technique
AB aka Spaced Pair Mic Placement
- Good for wide stereo images
- Captures more of the stereo image than an “XY” pair
- Susceptible to phase cancellation. Listen and look at the waveforms, adjust if needed
- Good for creating unnatural images (for experimental sound design)
- Acoustic instrument applications:
- Guitar: one mic near the body, one near the neck: spaced 30 cm apart, 10 cm from
instrument - Grand piano: one mic over lower strings, one over higher strings
- Large ensembles: usually spaced 6-8 feet/1.8-2.5 meters apart
Microphone Placement “ORTF”
Spaced out X shape
* ORTF (Office de Radiodiffusion Télévision Française)
* 2 cardioid microphones
* Near-coincident
* Capsules are 17cm apart, at 110-degrees
* Emulates position of human ears
* Slightly wider image than XY
