1. More Microphone Design/Application Transient Response to Phantom Power

2. 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.

3. Microphone Output Characteristics Sensitivity Rating Equivalent Noise Rating Overload characteristics Microphone Impedance

4. 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.

5. 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.

6. 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.

7. 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)

8. 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.

9. 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.

10. 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.

11. 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.