science

Silence suppression

Silence suppression 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 Silence suppression rather than just read about it. In short: The term silence suppression is used in telephony to describe the process of not transmitting information over the network when one of the parties involved in a telephone call is not speaking, thereby reducing bandwidth usage. Voice is carried over a digital telephone network by converting the analog signal to a digital signal which is then packetized and sent electronically over the network.

Key takeaways

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

Reference excerpt

The term silence suppression is used in telephony to describe the process of not transmitting information over the network when one of the parties involved in a telephone call is not speaking, thereby reducing bandwidth usage. Voice is carried over a digital telephone network by converting the analog signal to a digital signal which is then packetized and sent electronically over the network. The analogue signal is re-created at the receiving end of the network. When one of the parties does not speak, background noise is picked up and sent over the network. This is inefficient as this signal carries no useful information and thus, bandwidth is wasted. Given that typically only one party in a conversation speaks at any one time, silence suppression can achieve overall bandwidth savings in the order of 50% over the duration of a telephone call. (While both parties may sometimes speak at the same time, there are times when both parties are silent.) Silence suppression is achieved by recognizing the lack of speech through a speech processing mechanism called voice activity detection (VAD) which dynamically monitors background noise and sets a corresponding speech detection threshold. This technique is also known as speech activity detection (SAD). A similar principle is used for Discontinuous Reception and discontinuous transmission in GSM mobile telephone systems. For further bandwidth gains, silence suppression is normally done after echo cancellation.

Drawbacks Background noise detection may be difficult in some circumstances (relatively low speech level, or relatively high background noise level, for example). When silence suppression is active, the line appears to have gone dead at the other (egress) end of the call. For this reason, so-called comfort noise needs to be generated to compensate for the lack of background noise. The ingress end must therefore signal the egress end that silence suppression is in effect. For best results, the level of comfort noise being generated on egress should match that of the background noise at the ingress end. Speech activity detection must occur very quickly, otherwise clipping might occur. Speech activity detection does not work well on non-speech calls (fax or modem communication, for example). Thus, silence suppression is generally an optional feature on telephony devices. In some cases, it is automatically turned on based on the characteristics of a call.

See also Comfort noise Talkspurt Voice activity detection

External links Silence suppression and comfort noise generation (International Engineering Consortium on-line education topic)

Worked examples

Example 1 — a first encounter with Silence suppression

Start with the simplest possible case. Write down what Silence suppression 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 Silence suppression 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 Silence suppression 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 Silence suppression

In research: Silence suppression 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 Silence suppression 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: Silence suppression is common in secondary-school and first-year university syllabi. It links to neighbouring topics Telephony, so understanding it makes those chapters shorter.
In everyday life: Look for Silence suppression 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 Silence suppression in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Silence suppression 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 Silence suppression out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Silence suppression in simple terms?

Why does Silence suppression 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 Silence suppression?

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 Silence suppression.