The term microphone preamplifier can either refer to the electronic circuitry within a microphone, or to a separate device or circuit that the microphone is connected to. In either instance, the purpose of the microphone preamplifier is the same.
A microphone preamplifier is a
sound engineering device that prepares a
microphone
A microphone, colloquially called a mic (), or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publi ...
signal
A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology.
In ...
to be processed by other equipment. Microphone signals are often too weak to be transmitted to units such as
mixing console
A mixing console or mixing desk is an electronic device for Audio mixing (recorded music), mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals fro ...
s and
recording devices with adequate quality. Preamplifiers increase a microphone signal to
line level
Line level is the specified Audio power, strength of an audio signal used to transmit analog (signal), analog sound between audio components such as compact disc, CD and Digital Versatile Disc, DVD players, television sets, audio amplifiers, and ...
(i.e. the level of signal strength required by such devices) by providing stable
gain while preventing induced noise that would otherwise distort the signal.
[Ballou, 1987, pp. 506–507.] For additional discussion of signal level, see
Gain stage
In audio engineering, a gain stage is a point during an audio signal flow that the engineer can make adjustments to the level,Thompson, Dan (2005). ''Understanding Audio''. Berklee Press. . such as a fader on a mixing console or in a DAW. Gain st ...
.
A microphone preamplifier is colloquially called a microphone preamp, mic preamp, micamp, ''preamp'' (not to be confused with a
control amplifier in
high-fidelity
High fidelity (hi-fi or, rarely, HiFi) is the high-quality reproduction of sound. It is popular with audiophiles and home audio enthusiasts. Ideally, high-fidelity equipment has inaudible noise and distortion, and a flat (neutral, uncolored) f ...
reproduction equipment), mic pre and pre.
Technical details
The output voltage on a
dynamic microphone
A microphone, colloquially called a mic (), or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publ ...
may be very low, typically in the 1 to 100 microvolt range. A microphone preamplifier increases that level by up to 70
dB, to anywhere up to 10 volts. This stronger signal is used to drive equalization circuitry within an
audio mixer
A mixing console or mixing desk is an electronic device for mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals from electric or electronic instr ...
, to drive external audio effects, and to sum with other signals to create an audio mix for
audio recording
Sound recording and reproduction is the electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording t ...
or for
live sound
Live sound mixing is the blending of multiple sound sources by an audio engineer using a mixing console or software. Sounds that are mixed include those from instruments and voices which are picked up by microphones (for drum kit, lead vocals an ...
.
Functions
In addition to providing gain for the microphone signal, a microphone preamplifier as found in a sound mixer or as a discrete component typically also provides power to the microphone in the form of either 24 or 48 volt
phantom power
Phantom power, in the context of Professional audio, professional audio equipment, is Direct current, DC electric power equally applied to both signal wires in Balanced line, balanced microphone cables, forming a phantom circuit, to power m ...
.
In use
A microphone is a
transducer
A transducer is a device that Energy transformation, converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
Transducers are often employed at the boundaries of automation, M ...
and as such is the source of much of the coloration of an audio mix. Most
audio engineer
An audio engineer (also known as a sound engineer or recording engineer) helps to produce a recording or a live performance, balancing and adjusting sound sources using equalization, dynamics processing and audio effects, mixing, reproduc ...
s would assert that a microphone preamplifier also affects the sound quality of an audio mix. A preamplifier might load the microphone with low impedance, forcing the microphone to work harder and so change its tone quality. A preamplifier might add coloration by adding a different characteristic than the audio mixer's built-in preamplifiers. Some microphones, for example condensers, must be used in conjunction with an impedance matching preamplifier to function correctly.
Some preamplifiers exist as one part of a
channel strip
A ''channel strip'' is a device that allows the output of an audio device to be amplified to a line level and integrated into some other system. An audio channel strip may be a stand-alone unit or one of many units built into a mixing desk. It ...
, which can include other kinds of audio recording devices such as
compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Many compressors can be staged, that is, the gas is compressed several times in steps o ...
s,
equalization (EQ),
noise gate
A noise gate or simply gate is an electronic device or software that is used to control the amplitude, volume of an audio signal. Comparable to a limiter, which attenuates signals ''above'' a threshold, such as loud attacks from the start of mu ...
s, and
enhancers
In genetics, an enhancer is a short (50–1500 bp) region of DNA that can be bound by proteins ( activators) to increase the likelihood that transcription of a particular gene will occur. These proteins are usually referred to as transcriptio ...
.
References
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{{Music technology
Audio amplifiers
Microphones