Telecommunication | Technology, Examples, Devices, & Facts

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border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/technology/telecommunication">telecommunication</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/technology/telecommunication">Introduction</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref76266"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/technology/telecommunication#ref76266">Analog-to-digital conversion</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref76267"><a class="w-100 link-gray-900" href="/technology/telecommunication#ref76267">Sampling</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76268"><a class="w-100 link-gray-900" href="/technology/telecommunication#ref76268">Quantization</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76269"><a class="w-100 link-gray-900" href="/technology/telecommunication/Bit-mapping">Bit mapping</a></li></ul></div></li><li data-target="#ref76270"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/technology/telecommunication/Bit-mapping#ref76270">Source encoding</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref76271"><a class="w-100 link-gray-900" href="/technology/telecommunication/Bit-mapping#ref76271">Huffman codes</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76272"><a class="w-100 link-gray-900" href="/technology/telecommunication/Bit-mapping#ref76272">The Lempel-Ziv algorithm</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76273"><a class="w-100 link-gray-900" href="/technology/telecommunication/Bit-mapping#ref76273">Run-length codes</a></li></ul></div></li><li data-target="#ref76274"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/technology/telecommunication/Channel-encoding">Channel encoding</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref76275"><a class="w-100 link-gray-900" href="/technology/telecommunication/Channel-encoding#ref76275">Repetition codes</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76276"><a class="w-100 link-gray-900" href="/technology/telecommunication/Channel-encoding#ref76276">The Hamming code</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76277"><a class="w-100 link-gray-900" href="/technology/telecommunication/Channel-encoding#ref76277">Convolutional encoding</a></li></ul></div></li><li data-target="#ref76278"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/technology/telecommunication/Modulation">Modulation</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref76279"><a class="w-100 link-gray-900" href="/technology/telecommunication/Modulation#ref76279">Analog modulation</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76280"><a class="w-100 link-gray-900" href="/technology/telecommunication/Modulation#ref76280">Digital modulation</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref76281"><a class="w-100 link-gray-900" href="/technology/telecommunication/Modulation#ref76281">Amplitude-shift keying</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref76282"><a class="w-100 link-gray-900" href="/technology/telecommunication/Modulation#ref76282">Frequency-shift keying</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref76283"><a class="w-100 link-gray-900" href="/technology/telecommunication/Modulation#ref76283">Phase-shift keying</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref76284"><a class="w-100 link-gray-900" href="/technology/telecommunication/Modulation#ref76284">Advanced methods</a></li></ul></li></ul></div></li><li data-target="#ref76285"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/technology/telecommunication/Multiplexing">Multiplexing</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref76286"><a class="w-100 link-gray-900" href="/technology/telecommunication/Multiplexing#ref76286">Frequency-division multiplexing</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76287"><a class="w-100 link-gray-900" href="/technology/telecommunication/Multiplexing#ref76287">Time-division multiplexing</a></li></ul></div></li><li data-target="#ref76288"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/technology/telecommunication/Multiple-access">Multiple access</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref76289"><a class="w-100 link-gray-900" href="/technology/telecommunication/Multiple-access#ref76289">Frequency-division multiple access</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76290"><a class="w-100 link-gray-900" href="/technology/telecommunication/Multiple-access#ref76290">Time-division multiple access</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref76291"><a class="w-100 link-gray-900" href="/technology/telecommunication/Multiple-access#ref76291">Code-division multiple access</a></li></ul></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/technology/telecommunication/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/telecommunication">Quick Facts & Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a 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src="https://cdn.britannica.com/16/4616-004-39B3985A/steps-conversion-analog-signal-intervals-receiver-value.jpg" alt="Basic steps in analog-to-digital conversionAn analog signal is sampled at regular intervals. The amplitude at each interval is quantized, or assigned a value, and the values are mapped into a series of binary digits, or bits. The information is transmitted as a digital signal to the receiver, where it is decoded and the analog signal reconstituted." height="50" /> </a> <a href="https://cdn.britannica.com/18/4618-050-5E36758C/signal-modulation-methods-binary-digits-amplitudes-series.jpg" data-href="/media/1/585799/3693" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/18/4618-004-79CDE7BF/signal-modulation-methods-binary-digits-amplitudes-series.jpg" alt="digital signal modulation" height="50" /> </a> <a href="https://cdn.britannica.com/19/4619-004-41851F3A/multiplexing-North-American-frequency-division-telephone-system-voice.jpg" data-href="/media/1/585799/3694" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/19/4619-004-41851F3A/multiplexing-North-American-frequency-division-telephone-system-voice.jpg" alt="Analog multiplexing, as employed in the North American telephone systemIn frequency-division multiplexing (FDM), 12 separate voice signals, each of 4-kilohertz bandwidth, are modulated onto carrier waves in the 60–108-kilohertz range. 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Let us know if you have suggestions to improve this article (requires login). </div> <div class="type-menu"> <label for="feedback-type" class="label mb-10">Feedback Type</label> <select id="feedback-type" class="form-select mb-30" name="feedbackTypeId" required> <option value="" selected="selected">Select a type (Required)</option> <option value="1">Factual Correction</option> <option value="2">Spelling/Grammar Correction</option> <option value="3">Link Correction</option> <option value="4">Additional Information</option> <option value="5">Other</option> </select> </div> <label for="feedback" class="label mb-10">Your Feedback</label> <textarea id="feedback" class="form-control mb-30" name="feedback" maxlength="3000" rows="7" required></textarea> <button class="btn btn-blue" type="submit">Submit Feedback</button> </form> <div class="success-messaging d-none mt-30"> <div class="title">Thank you for your feedback</div> <p>Our editors will review what you’ve submitted and determine whether to revise the article.</p> </div> </div> </div> <div class="md-websites-modal size-lg d-none"> <div class="md-modal-body"> <div class="h2 font-serif pb-15 border-bottom font-weight-bold"> External Websites </div> <div class="pb-20"> <ul class="list-unstyled mt-20 lh-lg"> <li><a class="external" href="https://www.umsl.edu/~joshik/msis480/chapt07.htm" target="_blank" rel="noopener ">University of Missouri-St. Louis - Telecommunications, the Internet, and Information System Architecture</a></li> <li><a class="external" href="https://www.academia.edu/4768572/Telecommunication_Introduction" target="_blank" rel="noopener ">Academia - Telecommunication Introduction</a></li> <li><a class="external" href="https://www.eolss.net/sample-chapters/c05/e6-108-02-00.pdf" target="_blank" rel="noopener ">UNESCO-EOLSS - Fundamentals of Telecommunications</a></li> <li><a class="external" href="https://ops.fhwa.dot.gov/publications/telecomm_handbook/chapter2_01.htm" target="_blank" rel="noopener ">Federal Highway Administration - Office of Operations - Fundamentals of Telecommunications</a></li> <li><a class="external" href="https://pmc.ncbi.nlm.nih.gov/articles/PMC4296789/" target="_blank" rel="noopener ">National Center for Biotechnology Information - PubMed Central - Telecommunications and Internet Broadband Policy: Sorting Out the Pieces for Telerehabilitation</a></li> <li><a class="external" href="https://www.theiet.org/media/11266/selected-landmarks-in-telecommunications.pdf" target="_blank" rel="noopener ">The Institute of Engineering and Technology - Selected landmarks in The History of Telecommunications</a></li> <li><a class="external" href="https://workforce.libretexts.org/Bookshelves/Information_Technology/Computer_Applications/Introduction_to_Computer_Applications_and_Concepts_(Lumen)/07%3A_Networks_and_Security/7.02%3A_Reading-_Networks_and_Telecommunications" target="_blank" rel="noopener ">Workforce LibreTexts - Reading- Networks and Telecommunications</a></li> <li><a class="external" href="https://utsa.pressbooks.pub/networking/chapter/history-of-telecommunications/" target="_blank" rel="noopener ">UTSA Pressbooks - History of Telecommunications</a></li> <li><a class="external" href="https://www.thecanadianencyclopedia.ca/en/article/telecommunications" target="_blank" rel="noopener ">The Canadian Encyclopedia - Telecommunication</a></li> </ul> </div> <div class="md-websites-ebk-title">Britannica Websites</div> <div class="md-websites-ebk-subtitle">Articles from Britannica Encyclopedias for elementary and high school students.</div> <ul class="list-unstyled bps-topic-web-sites lh-lg"> <li><a class="external" href="https://kids.britannica.com/kids/article/telecommunication/390860" target="_blank" rel="noopener">telecommunication - Children's Encyclopedia (Ages 8-11)</a></li> <li><a class="external" href="https://kids.britannica.com/students/article/telecommunication/277287" target="_blank" rel="noopener">telecommunication - Student Encyclopedia (Ages 11 and up)</a></li> </ul> </div> </div> </div> </div> <div class="toc-header-marker"></div> <button class="ai-ask-button btn btn-sm border-2 btn-outline-red-400 border-red-400 d-none mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10 px-sm-5 px-md-10 js-header-ai-ask-button"> Ask the Chatbot a Question </button> <div class="caption alternate-titles">Also known as: electronic communication</div> <div class="md-byline module-spacing "> <div class="font-serif font-12"> <span class="written-by text-gray-700"> Written by </span> <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup gtm-byline font-12 byline-contributor" href="/contributor/David-E-Borth/4163" > <div class="editor-title font-16 font-weight-bold">David E. Borth</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Corporate Vice President and Director, Communications Research Laboratories, Motorola Inc., Schaumburg, Illinois. Coauthor of <i>Introduction to Spread Spectrum Communications.</i></div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> David E. Borth</span>, <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup gtm-byline font-12 byline-contributor" href="/contributor/Wayne-Eric-Stark/4216" > <div class="editor-title font-16 font-weight-bold">Wayne Eric Stark</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Professor of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor. Coauthor of various articles on telecommunications technology.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Wayne Eric Stark</span><span class="text-gray-700 mx-5">•</span><a class="see-all border-gray-700 gtm-byline" rel="nofollow" href="https://www.britannica.com/technology/telecommunication/additional-info#contributors">All</a> </div> <div class="font-serif font-12 text-gray-700"> <span class="qa-fact-checked-by">Fact-checked by</span> <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup font-12" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <span class="text-gray-700"> Last Updated: <time datetime="2025-01-31T00:00:00CST" >Jan 31, 2025</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/technology/telecommunication/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn btn-sm border-2 btn-outline-red-400 border-red-400 module-spacing js-inline-ai-ask-button p-10 ml-5"> Ask the Chatbot </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Key People: </dt> <dd><a href="/biography/Guglielmo-Marconi" topicid="364287">Guglielmo Marconi</a></dd> <dd><a href="/money/Carlos-Slim-Helu" topicid="915128">Carlos Slim Helú</a></dd> <dd><a href="/biography/Saad-al-Hariri" topicid="1383553">Saad al-Hariri</a></dd> <dd><a href="/money/Morita-Akio" topicid="392429">Morita Akio</a></dd> <dd><a href="/money/Anousheh-Ansari" topicid="1267667">Anousheh Ansari</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/technology/television-technology" topicid="1262241">television</a></dd> <dd><a href="/technology/broadcasting" topicid="80543">broadcasting</a></dd> <dd><a href="/technology/telephone" topicid="585993">telephone</a></dd> <dd><a href="/technology/Internet" topicid="291494">Internet</a></dd> <dd><a href="/technology/radio-technology" topicid="1262240">radio technology</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/telecommunication"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref608159"></span>telecommunication</strong>, <a href="https://www.britannica.com/science/science" class="md-crosslink autoxref " data-show-preview="true">science</a> and practice of transmitting information by electromagnetic means. Modern telecommunication centres on the problems involved in transmitting large volumes of information over long distances without damaging loss due to noise and interference. The basic components of a modern digital telecommunications system must be capable of transmitting voice, data, radio, and television signals. <span id="ref608163"></span><a href="https://www.britannica.com/technology/digital-transmission" class="md-crosslink ">Digital transmission</a> is employed in order to achieve high reliability and because the cost of digital <a href="https://www.britannica.com/technology/switching" class="md-crosslink autoxref " data-show-preview="true">switching</a> systems is much lower than the cost of <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="analog" href="https://www.merriam-webster.com/dictionary/analog" data-type="MW">analog</a> systems. In order to use digital transmission, however, the analog signals that make up most voice, radio, and television <a href="https://www.britannica.com/topic/communication" class="md-crosslink autoxref " data-show-preview="true">communication</a> must be subjected to a process of analog-to-digital conversion. (In <a href="https://www.britannica.com/technology/data-transmission" class="md-crosslink autoxref " data-show-preview="true">data transmission</a> this step is bypassed because the signals are already in digital form; most television, radio, and voice communication, however, use the analog system and must be digitized.) In many cases, the digitized signal is passed through a source encoder, which employs a number of formulas to reduce <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="redundant" href="https://www.merriam-webster.com/dictionary/redundant" data-type="MW">redundant</a> binary information. After source encoding, the digitized signal is processed in a channel encoder, which introduces redundant information that allows errors to be detected and corrected. The encoded signal is made suitable for transmission by <a href="https://www.britannica.com/technology/modulation-communications" class="md-crosslink autoxref " data-show-preview="true">modulation</a> onto a <a href="https://www.britannica.com/technology/carrier-wave" class="md-crosslink autoxref " data-show-preview="true">carrier wave</a> and may be made part of a larger signal in a process known as <span id="ref608166"></span><a href="https://www.britannica.com/technology/multiplexing" class="md-crosslink " data-show-preview="true">multiplexing</a>. The multiplexed signal is then sent into a multiple-access transmission channel. After transmission, the above process is reversed at the receiving end, and the information is extracted.</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">This article describes the components of a digital telecommunications system as outlined above. For details on specific applications that utilize telecommunications systems, see the articles <a href="https://www.britannica.com/technology/telephone" class="md-crosslink " data-show-preview="true">telephone</a>, <a href="https://www.britannica.com/technology/telegraph" class="md-crosslink " data-show-preview="true">telegraph</a>, <a href="https://www.britannica.com/technology/fax" class="md-crosslink " data-show-preview="true">fax</a>, <a href="https://www.britannica.com/technology/broadcasting" class="md-crosslink " data-show-preview="true">radio</a>, and <a href="https://www.britannica.com/technology/television-technology" class="md-crosslink " data-show-preview="true">television</a>. Transmission over electric <a href="https://www.britannica.com/technology/wire" class="md-crosslink autoxref " data-show-preview="true">wire</a>, <a href="https://www.britannica.com/science/radio-wave" class="md-crosslink autoxref " data-show-preview="true">radio wave</a>, and optical fibre is discussed in <a href="https://www.britannica.com/topic/telecommunications-media" class="md-crosslink " data-show-preview="true">telecommunications media</a>. For an overview of the types of networks used in information transmission, see <a href="https://www.britannica.com/technology/telecommunications-network" class="md-crosslink " data-show-preview="true">telecommunications network</a>.</p><span class="marker MOD2 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref76266"><h2 class="h1"><span id="ref608167"></span><a href="https://www.britannica.com/technology/analogue-to-digital-conversion" class="md-crosslink ">Analog-to-digital conversion</a></h2> <span class="marker PREMOD3 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="3692" data-asm-type="image"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/16/4616-004-39B3985A/steps-conversion-analog-signal-intervals-receiver-value.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/585799/3692"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/16/4616-004-39B3985A/steps-conversion-analog-signal-intervals-receiver-value.jpg"><img src="https://cdn.britannica.com/16/4616-004-39B3985A/steps-conversion-analog-signal-intervals-receiver-value.jpg?w=300" alt="Basic steps in analog-to-digital conversionAn analog signal is sampled at regular intervals. The amplitude at each interval is quantized, or assigned a value, and the values are mapped into a series of binary digits, or bits. The information is transmitted as a digital signal to the receiver, where it is decoded and the analog signal reconstituted." data-width="280" data-height="520" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/16/4616-004-39B3985A/steps-conversion-analog-signal-intervals-receiver-value.jpg" data-href="/media/1/585799/3692">Basic steps in analog-to-digital conversionAn analog signal is sampled at regular intervals. The amplitude at each interval is quantized, or assigned a value, and the values are mapped into a series of binary digits, or bits. The information is transmitted as a digital signal to the receiver, where it is decoded and the analog signal reconstituted.</a><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">In transmission of <a href="https://www.britannica.com/topic/speech-language" class="md-crosslink autoxref " data-show-preview="true">speech</a>, audio, or video information, the object is high fidelity—that is, the best possible reproduction of the original message without the <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="degradations" href="https://www.merriam-webster.com/dictionary/degradations" data-type="MW">degradations</a> imposed by signal <span id="ref608168"></span><a href="https://www.britannica.com/technology/distortion-communications" class="md-crosslink " data-show-preview="true">distortion</a> and <span id="ref608169"></span><a href="https://www.britannica.com/science/noise-acoustics" class="md-crosslink " data-show-preview="true">noise</a>. The basis of relatively noise-free and distortion-free telecommunication is the <span id="ref608170"></span>binary signal. The simplest possible signal of any kind that can be employed to transmit messages, the binary signal consists of only two possible values. These values are represented by the binary digits, or <span id="ref608171"></span><a href="https://www.britannica.com/technology/bit-communications" class="md-crosslink " data-show-preview="true">bits</a>, 1 and 0. Unless the noise and distortion picked up during transmission are great enough to change the binary signal from one value to another, the correct value can be determined by the <a href="https://www.britannica.com/technology/receiver" class="md-crosslink autoxref " data-show-preview="true">receiver</a> so that perfect reception can occur.</p><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">If the information to be <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="transmitted" href="https://www.britannica.com/dictionary/transmitted" data-type="EB">transmitted</a> is already in <a href="https://www.britannica.com/art/binary-form" class="md-crosslink autoxref " data-show-preview="true">binary form</a> (as in data communication), there is no need for the signal to be digitally encoded. But ordinary voice communications taking place by way of a telephone are not in binary form; neither is much of the information gathered for transmission from a space probe, nor are the television or radio signals gathered for transmission through a satellite link. Such signals, which continually vary among a range of values, are said to be analog, and in digital communications systems analog signals must be converted to digital form. The process of making this signal conversion is called analog-to-digital (A/D) conversion.</p><span class="marker MOD4 mod-inline"></span> <section data-level="2" id="ref76267"><h2 class="h2"><span id="ref608172"></span><a href="https://www.britannica.com/technology/sampling-communications" class="md-crosslink ">Sampling</a></h2> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">Analog-to-digital <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="conversion" href="https://www.britannica.com/dictionary/conversion" data-type="EB">conversion</a> begins with sampling, or measuring the amplitude of the analog <span id="ref608173"></span><a href="https://www.britannica.com/science/wave-physics" class="md-crosslink " data-show-preview="true">waveform</a> at equally spaced discrete instants of time. The fact that samples of a continually varying wave may be used to represent that wave relies on the assumption that the wave is constrained in its rate of variation. Because a communications signal is actually a complex wave—essentially the sum of a number of component sine waves, all of which have their own precise amplitudes and phases—the rate of variation of the complex wave can be measured by the frequencies of oscillation of all its components. The difference between the maximum rate of oscillation (or highest frequency) and the minimum rate of oscillation (or lowest frequency) of the sine waves making up the signal is known as the <span id="ref608174"></span><a href="https://www.britannica.com/technology/bandwidth" class="md-crosslink " data-show-preview="true">bandwidth</a> (<em>B</em>) of the signal. <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="Bandwidth" href="https://www.britannica.com/dictionary/Bandwidth" data-type="EB">Bandwidth</a> thus represents the maximum <a href="https://www.britannica.com/science/frequency-physics" class="md-crosslink autoxref " data-show-preview="true">frequency</a> range occupied by a signal. In the case of a voice signal having a minimum frequency of 300 hertz and a maximum frequency of 3,300 hertz, the bandwidth is 3,000 hertz, or 3 kilohertz. Audio signals generally occupy about 20 kilohertz of bandwidth, and standard video signals occupy approximately 6 million hertz, or 6 megahertz.</p><div class="module-spacing"> </div><span class="marker MOD5 mod-inline"></span> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">The concept of bandwidth is central to all telecommunication. In analog-to-digital conversion, there is a fundamental theorem that the analog signal may be uniquely represented by discrete samples spaced no more than one over twice the bandwidth (1/2<em>B</em>) apart. This theorem is commonly referred to as the <span id="ref608175"></span><a href="https://www.britannica.com/topic/sampling-theorem" class="md-crosslink ">sampling theorem</a>, and the sampling interval (1/2<em>B</em> seconds) is referred to as the <span id="ref608176"></span><a href="https://www.britannica.com/technology/Nyquist-interval" class="md-crosslink ">Nyquist interval</a> (after the Swedish-born American electrical engineer <a href="https://www.britannica.com/biography/Harry-Nyquist" class="md-crosslink " data-show-preview="true">Harry Nyquist</a>). As an example of the Nyquist interval, in past telephone practice the bandwidth, commonly fixed at 3,000 hertz, was sampled at least every 1/6,000 second. In current practice 8,000 samples are taken per second, in order to increase the frequency range and the <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="fidelity" href="https://www.merriam-webster.com/dictionary/fidelity" data-type="MW">fidelity</a> of the speech representation.</p><span class="marker MOD6 mod-inline"></span></section> <section data-level="2" id="ref76268"><h2 class="h2"><span id="ref608177"></span>Quantization</h2> <span class="marker PREMOD7 mod-inline"></span><p class="topic-paragraph">In order for a sampled signal to be stored or transmitted in digital form, each sampled amplitude must be converted to one of a finite number of possible values, or levels. For ease in conversion to binary form, the number of levels is usually a power of 2—that is, 8, 16, 32, 64, 128, 256, and so on, depending on the degree of precision required. In digital transmission of <span id="ref608178"></span>voice, 256 levels are commonly used because tests have shown that this provides adequate fidelity for the average telephone listener.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=august-2024">Subscribe</a> </div> </div> </div> </DIV></div><div class="one-good-fact-module"> </div><span class="marker MOD7 mod-inline"></span> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">The input to the quantizer is a sequence of sampled amplitudes for which there are an <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="infinite" href="https://www.merriam-webster.com/dictionary/infinite" data-type="MW">infinite</a> number of possible values. The output of the quantizer, on the other hand, must be restricted to a finite number of levels. Assigning infinitely variable amplitudes to a limited number of levels inevitably introduces inaccuracy, and inaccuracy results in a corresponding amount of signal distortion. (For this reason quantization is often called a “lossy” system.) The degree of inaccuracy depends on the number of output levels used by the quantizer. More quantization levels increase the accuracy of the representation, but they also increase the storage capacity or transmission speed required. Better performance with the same number of output levels can be achieved by judicious placement of the output levels and the amplitude <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="thresholds" href="https://www.merriam-webster.com/dictionary/thresholds" data-type="MW">thresholds</a> needed for assigning those levels. This placement in turn depends on the nature of the waveform that is being quantized. Generally, an optimal quantizer places more levels in amplitude ranges where the signal is more likely to occur and fewer levels where the signal is less likely. This technique is known as <span id="ref608179"></span>nonlinear quantization. Nonlinear quantization can also be accomplished by passing the signal through a compressor circuit, which amplifies the signal’s weak components and <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="attenuates" href="https://www.merriam-webster.com/dictionary/attenuates" data-type="MW">attenuates</a> its strong components. The compressed signal, now occupying a narrower <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="dynamic" href="https://www.merriam-webster.com/dictionary/dynamic" data-type="MW">dynamic</a> range, can be quantized with a uniform, or linear, spacing of thresholds and output levels. In the case of the telephone signal, the compressed signal is uniformly quantized at 256 levels, each level being represented by a sequence of eight bits. At the receiving end, the reconstituted signal is expanded to its original range of amplitudes. This sequence of compression and expansion, known as <span id="ref608180"></span>companding, can yield an effective dynamic range equivalent to 13 bits.</p><span class="marker MOD8 mod-inline"></span></section> </section><span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-simplify-root"></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article> </div> </div> </div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":1,"pagesTotal":6,"pageId":585799,"pageLength":1261,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-133/js/libs/jquery-3.5.0.min.js?v=3.133.48"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-133/dist/topic-page.js?v=3.133.48' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"C","adLeg":"C","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"PAGINATED","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":true,"hasAiTopQuestions":false,"hasSimplifyButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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