Sidetone is audible

feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...

to someone speaking or otherwise producing sound as an indication of active transmission. Sidetone is introduced by some communications circuits and anti-sidetone circuitry is used to control its level. Sidetone is expected behavior for telephone systems. Absence of sidetone can cause users to believe the call has been dropped or cause them to speak loudly. Too much sidetone can cause users to speak softly.

Telephony

telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunications services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is ...

, sidetone is the effect of sound picked up by the

telephone A telephone, colloquially referred to as a phone, is a telecommunications device that enables two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most ...

's transmitter (mouthpiece) and instantly introduced at a low electronic signal level into the receiver (earpiece) of the same handset, a form of electrical

through the

telephone hybrid In analog telephony, a telephone hybrid is the component at the ends of a subscriber line of the public switched telephone network (PSTN) that converts between two-wire and four-wire forms of bidirectional audio paths. When used in broadcast faci ...

.AT&T, ''Bell System Practices'', Section C30.001 Issue 1 (March 16, 1932) ''Common Battery Anti-Sidetone Stations'' Sidetone in early 19th century telephones was strong due to the type of circuit used in instruments. Anti-sidetone circuitry in the telephone hybrid brought sidetone under control in the early 20th century, leaving enough feedback signal to assure the user that the telephone is working. Almost all land-line (wired and wireless) telephones have employed sidetone, so it was an expected convention for cellular telephony, but is not standard. The amount of sidetone on land-lines is typically 8%, and is 4% for cellular phones. Usability experts believe that lack of adequate sidetone causes some people to shout or speak too loudly when using a cell phone, a behavior that is sometimes referred to as "cell yell". One of the benefits of sidetone-enabled phones is that a user knows a call has been dropped or ended if he or she no longer hears sidetone.

Comfort noise Comfort noise (or comfort tone) is synthetic background noise used in radio and wireless communications to fill the artificial silence in a transmission resulting from voice activity detection or from the audio clarity of modern digital lines. ...

provides a similar benefit. Sidetone is disabled when telephones are running in speakerphone mode to prevent direct acoustical feedback from the speaker to the microphone, resulting in howling. Sidetone can be, and often is, amplified for land-line phones for the hearing impaired.

Radiotelegraphy

wireless telegraphy Wireless telegraphy or radiotelegraphy is the transmission of text messages by radio waves, analogous to electrical telegraphy using electrical cable, cables. Before about 1910, the term ''wireless telegraphy'' was also used for other experimenta ...

(WT) and

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emer ...

, sidetone is the audible indication of a

continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particl ...

(CW) signal as the operator sends

Morse code Morse code is a telecommunications method which Character encoding, encodes Written language, text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code i ...

. As in telephony, sidetone serves as feedback to the operator that what they are sending is what is intended. It is designed to mimic the tone generated by a typical radio receiver when a CW signal is converted to the

intermediate frequency In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in Transmission (telecommunications), transmission or reception. The intermediate frequency is ...

(IF), then mixed with the

beat frequency oscillator In a radio receiver, a beat frequency oscillator or BFO is a dedicated electronic oscillator, oscillator used to create an audio frequency signal from Morse code radiotelegraphy (Continuous wave, CW) transmissions to make them audible. The signal ...

(BFO) frequency to generate a ''difference frequency'', which is audible over the radio receiver loudspeaker or headphones. Sidetone is also used on voice radio equipment to give the radio operator confidence that they are transmitting over the radio. The sidetone audio is typically derived from the transmit audio circuitry.

Public address systems

When a commentator,

announcer An announcer is a voice artist who relays information to the audience on a broadcast media programme or live event either on radio or television. Television and other media Some announcers work in television production, radio or filmmaki ...

, or MC for a public event may otherwise be able to hear their own voice in the delayed output from the loudspeakers, they may opt to use a headset which provides instant sidetone of their own voice, thus removing the distracting effect of greatly delayed auditory feedback from the loudspeakers.

References

{{reflist Telephony equipment Radio Feedback

Telephony

Radiotelegraphy

Public address systems

See also

References