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In digital and analog
audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum *Digital audio, representation of sound ...
, headroom refers to the amount by which the signal-handling capabilities of an audio system can exceed a designated
nominal level Nominal level is the operating level at which an electronic signal processing device is designed to operate. The electronic circuits that make up such equipment are limited in the maximum signal they can handle and the low-level internally genera ...
. Headroom can be thought of as a safety zone allowing transient audio peaks to exceed the nominal level without damaging the system or the audio signal, e.g., via
clipping Clipping may refer to: Words * Clipping (morphology), the formation of a new word by shortening it, e.g. "ad" from "advertisement" * Clipping (phonetics), shortening the articulation of a speech sound, usually a vowel * Clipping (publications) ...
. Standards bodies differ in their recommendations for nominal level and headroom.


Digital audio

In digital audio, headroom is defined as the amount by which digital full scale (FS) exceeds the nominal level in
decibel The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a po ...
s (dB). The
European Broadcasting Union The European Broadcasting Union (EBU; french: Union européenne de radio-télévision, links=no, UER) is an alliance of public service media organisations whose countries are within the European Broadcasting Area or who are members of the C ...
(EBU) specifies several nominal levels and resulting headroom for different applications.


Analog audio

In analog audio, headroom can mean low-level signal capabilities as well as the amount of extra power reserve available within the amplifiers that drive the loudspeakers.


Alignment level

Alignment level The alignment level in an audio signal chain or on an audio recording is a defined anchor point that represents a reasonable or typical level. It does not represent a particular sound level or signal level or digital representation, but it can ...
is an anchor point 9 dB below the nominal level, a reference level that exists throughout the system or broadcast chain, though it may imply different
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to mo ...
levels at different points in the analog chain. Typically, nominal (not alignment) level is 0 dB, corresponding to an analog
sine wave A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the ''sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often in ...
of voltage of 1.23 
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 RMS (+4  dBu or 3.47 volts
peak to peak The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of ampl ...
). In the digital realm, alignment level is −18 dBFS. * AL = analog level * SPL = sound pressure level


See also

*
A-weighting A-weighting is the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. A-weighting is applied to instrument-measured ...
*
Audio quality measurement Audio system measurements are a means of quantifying system performance. These measurements are made for several purposes. Designers take measurements so that they can specify the performance of a piece of equipment. Maintenance engineers make ...
*
Equal-loudness contour An equal-loudness contour is a measure of sound pressure level, over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. The unit of measurement for loudness levels is the phon and i ...
*
Fletcher–Munson curves An equal-loudness contour is a measure of sound pressure level, over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. The unit of measurement for loudness levels is the phon and ...
*
ITU-R 468 noise weighting ITU-R 468 (originally defined in CCIR recommendation 468-4, therefore formerly also known as CCIR weighting; sometimes referred to as CCIR-1k) is a standard relating to noise measurement, widely used when measuring noise in audio systems. The s ...
*
Loudness war The loudness war (or loudness race) is a trend of increasing audio levels in recorded music, which reduces audio fidelity and—according to many critics—listener enjoyment. Increasing loudness was first reported as early as the 1940s, with ...
*
Noise measurement In acoustics, noise measurement can be for the purpose of measuring environmental noise or measuring noise in the workplace. Applications include monitoring of construction sites, aircraft noise, road traffic noise, entertainment venues and neighb ...
*
Programme levels {{Unreferenced, date=November 2009 Programme level refers to the signal level that an audio source is transmitted or recorded at, and is important in audio if listeners of Compact Discs (CDs), radio and television are to get the best experience, w ...
*
Rumble measurement A rumble is a continuous deep, resonant sound, such as the sound made by heavy vehicles or thunder. In the context of audio reproduction rumble refers to a low frequency sound from the bearings inside a turntable. This is most noticeable in l ...
*
Weighting filter A weighting filter is used to emphasize or suppress some aspects of a phenomenon compared to others, for measurement or other purposes. Audio applications In each field of audio measurement, special units are used to indicate a weighted measure ...


References


Further reading

*BS.1726 "Signal level of digital audio accompanying television in international programme exchange" (2005) *BS.1864 "Operational practices for loudness in the international exchange of digital television programmes" (2010) *BS.1770-3 "Algorithms to measure audio programme loudness and true-peak audio level" (2012)


External links


EBU Recommendation R68-2000

AES Preprint 4828 - Levels in Digital Audio Broadcasting by Neil Gilchrist (not free)

EBU Recommendation R117-2006
(against
loudness war The loudness war (or loudness race) is a trend of increasing audio levels in recorded music, which reduces audio fidelity and—according to many critics—listener enjoyment. Increasing loudness was first reported as early as the 1940s, with ...
)
AES Convention Paper 5538 On Levelling and Loudness Problems at Broadcast Studios

EBU Tech 3282-E on EBU RDAT Tape Levels
{{Webarchive, url=https://web.archive.org/web/20090909130542/http://www.ebu.ch/CMSimages/en/tec_doc_t3282_tcm6-10542.pdf , date=2009-09-09
AES17-1998 (r2004): AES standard method for digital audio engineering -- Measurement of digital audio equipment
Audio engineering Broadcast engineering Sound production technology Sound recording Sound