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 is a two-port electronic circuit that uses electric power from a power su ...

gain,

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 ...

sensitivity, etc.) to get the units to match the input.

Examples

Equivalent input noise

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 ...

converts acoustical

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

electrical Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

energy. Microphones have some level of electrical

noise Noise is sound, chiefly unwanted, unintentional, or harmful sound considered unpleasant, loud, or disruptive to mental or hearing faculties. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrat ...

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, Voltage#Galvani potential vs. electrochemical potential, electric potential difference (voltage), and electromotive force in the International System of Units, International System of Uni ...

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

may be susceptible to electromagnetic interference which causes sonic artifacts. 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).

Examples

Equivalent input noise

Input-related interference level

References

Further reading