microphones

see also:

• sound dB meters
• sound
• sound recorders
• audio cables, adapters, bluetooth speakers, karaoke for camping
• birds making calls at night in Victoria

• microphones detect acoustic energy waves and convert these signals into electrical signals
• the far majority of microphones are restricted to the 20Hz-20,000Hz range of sound waves was these are the maximum range that humans can hear
• some microphones are designed for infrasonar ranges below 20Hz but to record below 3Hz you will probably need to resort to a seismometer

• acoustic principle or element
  • dynamic
    • sound more bass-prominent “radio voice” esp. if used up close to the mouth
    • tends to reject room echo noise (“reverb”) better as they are generally used closer to the mouth as they require more gain
  • condenser
    • usually require DC power - usually 48V DC “Phantom power” and this is usually shown by having “P48” or similar marked on the microphone
    • tend to pick up higher frequencies better and usually have an extended frequency response hence sound more crisp and bright
    • RF-biased
    • DC-biased
• polar pick up pattern
  • how directional the microphone is and how it can reduce rear and possibly side noise
  • cardioid pattern
    • weakest behind the microphone hence reduces sounds coming from behind
  • super cardioid pattern
    • creates a more narrow focused area than cardioid but also adds sensitivity to an area behind the microphone
    • often used in boom mics
• frequency response
  • how sensitive the mic is for all frequencies across the sound spectrum
  • too much boost in 5-10kHz overly emphasizes S sounds and can be annoying for those who have prominent high pitched S sounds (sibilance)
  • too much sensitivity in 40-200Hz is generally avoided by those who have a bass dominant voice
  • charts are usually averages of all production samples which may not apply well to your sample - expensive mics are often provided with its response chart as tested for that mic
• output impedance
  • for XLR based microphones this is usually 50-200 Ohms balanced
  • the input impedance on your recorder or preamp should be at least 10 x that of the mic's output impedance to achieve a “bridging impedance”
    • if it is not at least 10x, it may change the sound colour
• sensitivity or output level
  • this determines how much gain your pfe-amplifier will need to apply to achieve an optimal recording level
  • usually given in minus dB re 1 Volt/Pascal and in mV at a given dB SPL
  • the closer the minus dB value is to zero, the more sensitive it is
  • condenser mics are usually more sensitive than dynamic mics (dynamic mics often need at least 65dB of gain to be provided by the pre-amp)
• max sound pressure level (SPL)
  • a measure of the loudest sound that the mic can capture without distorting
  • for usual situations including singing, a max SPL of 120dB is usually adequate - many lavalier mics are below 120dB which may be inadequate for screams, etc
  • for very loud situations, you may need a mic with a max SPL of over 130-145dB
• self-noise or equivalent noise
  • all mics generate some noise - some mics are worse than others
  • this is not the noise the mic picks up from the surroundings
  • the best mics have a noise as low as 4dBA and acceptable mics are 16dBA or less (dbA is A weighted)
  • if the self-noise is higher than 20dBA, you may need to use noise reduction in post-processing
• power requirement
  • for condenser mics, this is usually 48V Phantom DC
  • providing 48V Phantom DC to a modern dynamic mic is unlikely to cause it any harm
  • professional grade lavalier mics usually require 3-5V DC plug in power - usually supplied by an attached battery pack which also transmits the signal by WiFi
    • inadequate voltage will degrade performance
• other features that may be present
  • high cut filter / low pass filter
    • this will remove some of the bass
    • a 250Hz filter is often used on mics which have excessive bass response when used close up
    • a 80Hz filter is often used for male voices to remove low pitched rumble (will not affect female voices)

• these transmit the audio signal from the microphone via radio waves to a radio receiver which will convert it back to an audio signal
• the transmission uses a high frequency carrier wave (eg. 433MHz, 2.4GHz) which is modulated such as by AM or FM
• the microphone generally has a pre-amplifier, radio transmitter and an antenna
• in a digital microphone, the audio analog signal is digitized and quantized before being sent to the radio transmitter which do not require an audio compressor (“compander”) and thus allows greater versatility and improved sound quality, especially for sources with more dynamic range or frequency range such as musical instruments rather than voice - for spoken voice, the sound quality difference between analog and digital is minimal. One of the downsides of digital is that they will introduce a small amount of latency and this will be additive to any system latency.
• unlike analog, digital has near zero static or pops from degraded transmission quality but at some point it will just drop out completely
• digital allows more channels in the same bandwidth