Transcript PowerPoint Presentation - More Microphone Design/Application

More Microphone
Design/Application
Transient Response to
Phantom Power
Transient Response
 Measure of how quickly a microphone’s
diaphragm will react to acoustic waveform.
 No accepted measure.
 Dynamic mic’s usually have larger diaphragm,
coil, and core. All add up to slower transient
response.
 Ribbon mic’s have thinner, lighter diaphragms.
Better transient response.
 Condenser mic’s have extremely lightweight
diaphragms, offering little mechanical resistance.
Generally have most accurate transient
response.
Microphone Output Characteristics
Sensitivity Rating
Equivalent Noise Rating
Overload characteristics
Microphone Impedance
Sensitivity Rating
The output level (in volts) produced by a
given (standardized) acoustic input signal
(in dB SPL).
Also specifies the amount of amplification
required to bring signal up line level (-10 dBV in
consumer systems; +4 dBm in pro systems)
Allows comparison of mic’s.
Sensitivity proportional to output-signal voltage.
Equivalent Noise Rating
Self-noise of device, measured in dB SPL
or dBA (weighted).
Generally not as pronounced as self-noise
of other stages in recording chain, but
more noticeable with technological
advancements.
Dynamic and Ribbon mic’s: s-n from
movement of electrons in ribbon or coil.
Condenser: s-n from built-in preamp.
Overload Characteristics
Upper limit of SPL that won’t distort.
Dynamic: typically around 140 dB
Condenser: typically doesn’t distort except
at very high levels. However, mic preamp
can be overloaded.
Pad or attenuation switch.
Pad reduces overall signal-to-noise ratio by
amount of pad.
Microphone Impedance
 Output impedance (sometimes called “Z”)
 Impedance measures resistance to signal flow.
 Important to match output (signal providing) capability to
input (signal receiving) capability (flow).
 Typical low: 50 Ω, 150 to 250 Ω
 Typical high: 20 to 50 kΩ (high)
 High impedance likely to pick up noise through cable.
 Low impedance can have long cable runs, but can pick
up electromagnetic noise. (shielded, twisted pair,
balanced line, 200 Ω used to prevent this)
Balanced Lines
 Balanced line: 3 wires to carry audio signal.
 Audio signal carried on two pins (wires), with different
polarities
Third pin is a ground.
Transformer/summing amp eliminates added noise
(equal polarity on both pins), responds to difference in
voltage between two pins.
XLR: 2 (+), 3 (-), 1 (ground)
TRS: tip-ring-sleeve 1/4”, ring (+), tip (-), sleeve (ground)
 Less susceptible to external noise.
Unbalanced Lines
Two wires to carry audio signal.
XLR: 2 is still +, but (-) pin connected to ground
(along with 1).
TS: tip-sleeve, tip (+), sleeve (ground)
More susceptible to external noise.
Microphone Preamps
 Mic output levels too low to drive line level input of
recording systems.
 Boost needed (30 - 60 dB)
 Most mixing consoles have “stock” pre’s.
 Recording professionals usually use “outboard”
(separate from mixer) preamps.
 Higher quality (lower noise/distortion)
 Special sound characteristics
 Special circuitry, or tube designs
 More control over input gain, filtering, perhaps compression.
 With the general demise of large, analog consoles, “classic”
pre’s from these boards are being marketed separately.
Phantom Power
 Power needed for condenser (and other “active”)
microphones.
 48V, DC, sent to mic condenser and impedance
preamp over pins 2 and 3.
Equally distributed through the use of identical value
resistors (often hand-chosen)
 Input preamp transformer looks for voltage
differences.
Matched 48V over both leads is eliminated at preamp
transformer. Doesn’t reach preamp gain stage.