Microphone

A microphone, sometimes called a mic (pronounced "mike"), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, tape recorders, hearing aids, motion picture production and in radio and television broadcasting.

Measurements and specifications

Because of differences in their construction, microphones have their own characteristic responses to sound. This difference in response produces non-uniform phase and frequency responses. In addition, mics are not uniformly sensitive to sound pressure, and can accept differing levels without distorting. Although for scientific applications microphones with a more uniform response are desirable, this is often not the case for music recording, as the non-uniform response of a microphone can produce a desirable coloration of the sound.

Related Topics:
Phase - Frequency

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A frequency response diagram plots the sound intensity in decibels over a range of frequencies (typically at least 0?20 kHz), generally for perfectly on-axis sound (sound arriving at 0° to the capsule). Frequency response may be less informatively stated textually like so: "20 Hz?20 kHz ±3 dB". This is interpreted as a (mostly) linear plot between the stated frequencies, with variations in amplitude of no more than 3 dB plus or minus. However, one cannot determine from this information how smooth the variations are, nor in what parts of the spectrum they occur. Note that commonly-made statements such as "20 Hz?20 kHz" are meaningless without a decibel measure.

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The self-noise or equivalent noise level is the sound level that creates the same output voltage as the inherent noise of the microphone. This represents the lowest point of the microphone's dynamic range, and is particularly important should you wish to record sounds that are quiet. The measure is often stated in dBA, which is a decibel scale frequency-weighted for how the ear hears. It may also state the air pressure at which the measure was taken, for example: "15 dBA at 20 µPa". The lower the number the better.

Related Topics:
DBA - Pa

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The maximum SPL (sound pressure level) the microphone can accept is measured for particular values of total harmonic distortion (THD), typically 1%. This is generally inaudible, so one can safely use the mic at this level without harming the recording. Example: "142 dB SPL peak (

Related Topics:
Sound pressure level - Total harmonic distortion - DB SPL

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The dynamic range of a mic is the difference in SPL between the noise floor and the maximum SPL. If stated on its own, for example "120 dB", it conveys significantly less information than having the self-noise and maximum SPL figures individually.

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Sensitivity indicates how well the mic converts acoustic pressure to output voltage. A high sensitivity mic creates more voltage and so will need less amplification at the mixer or recording device. This is a practical concern but not directly an indication of the mic's quality. Unfortunately there are two common measures. The international standard is made in mV per pascal at 1 kHz. A higher value indicates greater sensitivity. The older American method is made at 1 V/Pa and measured in dB, resulting in a negative value. Again, a higher value indicates greater sensitivity, so ?60 dB is more sensitive than ?70 dB.

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