science

Sidetone

Sidetone is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sidetone rather than just read about it. In short: Sidetone is audible feedback 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.

Key takeaways

Sidetone belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sidetone to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sidetone from memory before moving on to harder problems.

Reference excerpt

Sidetone is audible feedback 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 In telephony, sidetone is the effect of sound picked up by the telephone's transmitter (mouthpiece) and instantly introduced at a low electronic signal level into the receiver (earpiece) of the same handset, a form of electrical feedback through the telephone hybrid. 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 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 In wireless telegraphy (WT) and amateur radio, sidetone is the audible indication of a continuous wave (CW) signal as the operator sends Morse code. 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 (IF), then mixed with the beat frequency oscillator (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, 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.

Worked examples

Example 1 — a first encounter with Sidetone

Start with the simplest possible case. Write down what Sidetone claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sidetone before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sidetone ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sidetone

In research: Sidetone appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sidetone in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sidetone is common in secondary-school and first-year university syllabi. It links to neighbouring topics Feedback, Radio, Telephony equipment, so understanding it makes those chapters shorter.
In everyday life: Look for Sidetone outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sidetone in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sidetone means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sidetone out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sidetone in simple terms?

Why does Sidetone matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sidetone?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sidetone.