Equivalent input (also input-referred, referred-to-input (RTI), or input-related), is a method of referring to the signal or noise level at the output of a system as if it were due to an input to the same system. This input's value is called the Equivalent input. This is accomplished by removing all signal changes (e.g.
amplifier
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost t ...
gain,
transducer
A transducer is a device that 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, measurement, and cont ...
sensitivity, etc.) to get the units to match the input.
Examples
Equivalent input noise
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 publ ...
converts
acoustical
Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician ...
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...
to
electrical
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
energy. Microphones have some level of electrical
noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference aris ...
at their output. This noise may have contributions from random
diaphragm movement,
thermal noise
A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
, or a dozen other sources, but those can all be thought of as an imaginary acoustic noise source injecting sound into the (now noiseless) microphone. The units on this noise are no longer
volt
The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827).
Defin ...
s, but units of sound pressure (
pascals or
dBSPL
Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophon ...
), which can be directly compared to the desired sound pressure inputs. This is called ''equivalent input noise'' (EIN), or ''input-referred noise'' (IRN), or ''referred-to-input'' (RTI) ''noise''.
Input-related interference level
A device which uses 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 publ ...
may be susceptible to
electromagnetic interference which causes
sonic artifact
In sound and music production, sonic artifact, or simply artifact, refers to sonic material that is accidental or unwanted, resulting from the editing or manipulation of a sound.
Types
Because there are always technical restrictions in the way a ...
s. The problem is not in the microphone, but the interference level can be ''related'' back to the input to compare to the level of typical inputs to see how
audible
Audible may refer to:
* Audible (service), an online audiobook store
* Audible (American football), a tactic used by quarterbacks
* ''Audible'' (film), a short documentary film featuring a deaf high school football player
* Audible finish or ru ...
the artifact is. This is called ''input-related interference level'' (IRIL).
References
Further reading
* (67 pages)
*
Acoustics
Noise (electronics)
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