A reference tone is a pure tone corresponding to a known frequency, and produced at a stable

sound pressure level 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 hydropho ...

(volume), usually by specialized equipment.

In media

The most common reference tone in

audio engineering 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 sou ...

is a at −20 dB. It is meant to be used by audio engineers in order to adjust the playback equipment so that the accompanying

media Media may refer to: Communication * Media (communication), tools used to deliver information or data ** Advertising media, various media, content, buying and placement for advertising ** Broadcast media, communications delivered over mass e ...

is at a comfortable volume for the audience. In

video production Video production is the process of producing video content for video. It is the equivalent of filmmaking, but with video recorded either as analog signals on videotape, digitally in video tape or as computer files stored on optical discs, hard dri ...

, this tone is usually accompanied by a

test card A test card, also known as a test pattern or start-up/closedown test, is a television test signal, typically broadcast at times when the transmitter is active but no program is being broadcast (often at sign-on and sign-off). Used since the ea ...

so the video programming may be calibrated as well. It is sometimes played in sequence between a 100 Hz and 10 kHz tone to ensure an accurate response from the equipment at varying audio frequencies. This is also the "bleep" tone commonly used to censor obscene or sensitive audio content.

In music

Many

electronic tuner In music, an electronic tuner is a device that detects and displays the pitch of musical notes played on a musical instrument. "Pitch" is the perceived fundamental frequency of a musical note, which is typically measured in Hertz. Simple tuner ...

s used by musicians emit a tone of

440Hz A440 (also known as Stuttgart pitch) is the musical pitch corresponding to an audio frequency of 440 Hz, which serves as a tuning standard for the musical note of A above middle C, or A4 in scientific pitch notation. It is standardized by the ...

, corresponding to a pitch of A above

Middle C C or Do is the first note and semitone of the C major scale, the third note of the A minor scale (the relative minor of C major), and the fourth note (G, A, B, C) of the Guidonian hand, commonly pitched around 261.63 Hz. The actual fr ...

(A4). More sophisticated tuners offer a choice of other reference pitches to account for differences in

tuning Tuning can refer to: Common uses * Tuning, the process of tuning a tuned amplifier or other electronic component * Musical tuning, musical systems of tuning, and the act of tuning an instrument or voice ** Guitar tunings ** Piano tuning, adjusti ...

. Some specialized tuners offer pitches used commonly on a particular instrument (standard guitar tuning, fifth intervals for string instruments, the open tones for various brass instruments).

In telecommunications

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...

, a standard test tone is a pure tone with a standardized level generally used for

level alignment Level or levels may refer to: Engineering *Level (instrument), a device used to measure true horizontal or relative heights * Spirit level, an instrument designed to indicate whether a surface is horizontal or vertical *Canal pound or level *Reg ...

of single links and of links in

tandem Tandem, or in tandem, is an arrangement in which a team of machines, animals or people are lined up one behind another, all facing in the same direction. The original use of the term in English was in ''tandem harness'', which is used for two ...

. For standardized test signal levels and frequencies, see MIL-STD-188-100 for

United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national sec ...

(DOD) use, and the

Code of Federal Regulations In the law of the United States, the ''Code of Federal Regulations'' (''CFR'') is the codification of the general and permanent regulations promulgated by the executive departments and agencies of the federal government of the United States. ...

Title 47,

part 68 'Title 47 CFR Part 68'' is a section of the Code of Federal Regulations of the United States that regulate the direct electrical connection of telecommunications equipment and customer premises wiring with the public switched telephone network, cer ...

for other Government agencies.

References

{{reflist

External links

Downloadable reference tones
from

The Freesound Project Freesound is a collaborative repository of Creative Commons licensed audio samples, and non-profit organisation, with more than 500,000 sounds and effects (as of May 2021), and 8 million registered users (as of March 2019). Sounds are uploade ...

Audio engineering Music production Telecommunications standards