A reference tone is a

pure tone In psychoacoustics, a pure tone is a sound with a sinusoidal waveform; that is, a sine wave of constant frequency, phase-shift, and amplitude. By extension, in signal processing a single-frequency tone or pure tone is a purely sinusoidal signal ...

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 hydrophone ...

(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 soun ...

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 * Means of communication, tools and channels used to deliver information or data ** Advertising media, various media, content, buying and placement for advertising ** Interactive media, media that is inter ...

is at a comfortable volume for the audience. In

video production Video production is the process of producing video content. 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 drives, SSDs, ...

, 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 ear ...

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 tune ...

s used by musicians emit a tone of 440Hz, corresponding to a pitch of A above

Middle C C or Do is the first note 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 frequency has d ...

(A4). More sophisticated tuners offer a choice of other reference pitches to account for differences in tuning. 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, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

, a standard test tone is a

with a standardized level generally used for level alignment of single links and of links in

tandem Tandem, or in tandem, is an arrangement in which two or more animals, machines, or people are lined up one behind another, all facing in the same direction. ''Tandem'' can also be used more generally to refer to any group of persons or objects w ...

. For standardized test signal levels and frequencies, see

MIL-STD-188 MIL-STD-188 is a series of U.S. military standards relating to telecommunications. Purpose Faced with "past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the appl ...

-100 for

United States Department of Defense The United States Department of Defense (DoD, USDOD, or DOD) is an United States federal executive departments, executive department of the federal government of the United States, U.S. federal government charged with coordinating and superv ...

(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 regulatory law, regulations promulgated by the executive departments and agencies of the federal government of the ...

Title 47, part 68 for other Government agencies.

References

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External links

Downloadable reference tones
from The Freesound Project Audio engineering Music production Telecommunications standards