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class="vector-toc-numb">3.2</span> <span>In audio systems</span> </div> </a> <ul id="toc-In_audio_systems-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-In_video_systems" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#In_video_systems"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>In video systems</span> </div> </a> <ul id="toc-In_video_systems-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-In_forensics" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#In_forensics"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.4</span> <span>In forensics</span> </div> </a> <ul id="toc-In_forensics-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span 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<div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Electric or electromagnetic phenomenon</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output 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print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-More_citations_needed plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a></b>.<span class="hide-when-compact"> Please help <a href="/wiki/Special:EditPage/Mains_hum" title="Special:EditPage/Mains hum">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a>. Unsourced material may be challenged and removed.<br /><small><span class="plainlinks"><i>Find sources:</i> <a rel="nofollow" class="external text" href="https://www.google.com/search?as_eq=wikipedia&q=%22Mains+hum%22">"Mains hum"</a> – <a rel="nofollow" class="external text" href="https://www.google.com/search?tbm=nws&q=%22Mains+hum%22+-wikipedia&tbs=ar:1">news</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?&q=%22Mains+hum%22&tbs=bkt:s&tbm=bks">newspapers</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?tbs=bks:1&q=%22Mains+hum%22+-wikipedia">books</a> <b>·</b> <a rel="nofollow" class="external text" href="https://scholar.google.com/scholar?q=%22Mains+hum%22">scholar</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.jstor.org/action/doBasicSearch?Query=%22Mains+hum%22&acc=on&wc=on">JSTOR</a></span></small></span> <span class="date-container"><i>(<span class="date">March 2021</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <p><b>Mains hum</b>, <b>electric hum</b>, <b>cycle hum</b>, or <b>power line hum</b> is a sound associated with <a href="/wiki/Alternating_current" title="Alternating current">alternating current</a> which is twice the <a href="/wiki/Utility_frequency" title="Utility frequency">frequency</a> of the <a href="/wiki/Mains_electricity" title="Mains electricity">mains electricity</a>. The <a href="/wiki/Fundamental_frequency" title="Fundamental frequency">fundamental frequency</a> of this sound is usually double that of fundamental 50/60<span class="nowrap"> </span><a href="/wiki/Hertz" title="Hertz">Hz</a>, i.e., <span class="nowrap"> </span>100/120<span class="nowrap"> </span>Hz, depending on the local power-line frequency. The sound often has heavy <a href="/wiki/Harmonic" title="Harmonic">harmonic</a> content above 50/60<span class="nowrap"> </span>Hz. Due to the presence of mains current in mains-powered audio equipment as well as ubiquitous AC electromagnetic fields from nearby appliances and wiring, 50/60<span class="nowrap"> </span>Hz <a href="/wiki/Electrical_noise" class="mw-redirect" title="Electrical noise">electrical noise</a> can get into audio systems, and is heard as mains hum from their speakers. Mains hum may also be heard coming from powerful <a href="/wiki/Electric_power_grid" class="mw-redirect" title="Electric power grid">electric power grid</a> equipment such as utility <a href="/wiki/Transformer" title="Transformer">transformers</a>, caused by mechanical vibrations induced by <a href="/wiki/Magnetostriction" title="Magnetostriction">magnetostriction</a> in magnetic cores. Onboard aircraft (or spacecraft) the frequency heard is often higher pitched, due to the use of <a href="/wiki/400_Hz" class="mw-redirect" title="400 Hz">400 Hz</a> AC power in these settings because 400 Hz transformers are much smaller and lighter. </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><span><audio id="mwe_player_0" controls="" preload="none" data-mw-tmh="" class="mw-file-element" width="220" style="width:220px;" data-durationhint="6" data-mwtitle="50Hz_hum_square.ogg" data-mwprovider="wikimediacommons" resource="/wiki/File:50Hz_hum_square.ogg"><source src="//upload.wikimedia.org/wikipedia/commons/b/b7/50Hz_hum_square.ogg" type="audio/ogg; codecs="vorbis"" data-width="0" data-height="0" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/b/b7/50Hz_hum_square.ogg/50Hz_hum_square.ogg.mp3" type="audio/mpeg" data-transcodekey="mp3" data-width="0" data-height="0" /></audio></span><figcaption>50 Hz hum</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><span><audio id="mwe_player_1" controls="" preload="none" data-mw-tmh="" class="mw-file-element" width="220" style="width:220px;" data-durationhint="6" data-mwtitle="60Hz_hum_square.ogg" data-mwprovider="wikimediacommons" resource="/wiki/File:60Hz_hum_square.ogg"><source src="//upload.wikimedia.org/wikipedia/commons/7/72/60Hz_hum_square.ogg" type="audio/ogg; codecs="vorbis"" data-width="0" data-height="0" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/7/72/60Hz_hum_square.ogg/60Hz_hum_square.ogg.mp3" type="audio/mpeg" data-transcodekey="mp3" data-width="0" data-height="0" /></audio></span><figcaption>60 Hz hum</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><span><audio id="mwe_player_2" controls="" preload="none" data-mw-tmh="" class="mw-file-element" width="220" style="width:220px;" data-durationhint="6" data-mwtitle="400Hz_hum_square.ogg" data-mwprovider="wikimediacommons" resource="/wiki/File:400Hz_hum_square.ogg"><source src="//upload.wikimedia.org/wikipedia/commons/b/b4/400Hz_hum_square.ogg" type="audio/ogg; codecs="vorbis"" data-width="0" data-height="0" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/b/b4/400Hz_hum_square.ogg/400Hz_hum_square.ogg.mp3" type="audio/mpeg" data-transcodekey="mp3" data-width="0" data-height="0" /></audio></span><figcaption>400 Hz hum</figcaption></figure> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Causes">Causes</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=1" title="Edit section: Causes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Electric hum around <a href="/wiki/Transformer" title="Transformer">transformers</a> is caused by stray magnetic fields causing the enclosure and accessories to vibrate. <a href="/wiki/Magnetostriction" title="Magnetostriction">Magnetostriction</a> is a second source of vibration, in which the core iron changes shape minutely when exposed to magnetic fields. The intensity of the fields, and thus the "hum" intensity, is a function of the applied voltage. Due to the magnetic flux density is strongest twice every electrical cycle, the fundamental "hum" frequency will be twice the electrical frequency. Additional harmonics above 100/120<span class="nowrap"> </span>Hz will be caused by the non-linear behavior of most common magnetic materials. </p><p>Around high-voltage power lines, hum may be produced by <a href="/wiki/Corona_discharge" title="Corona discharge">corona discharge</a>. </p><p>In the realm of sound reinforcement (as in <a href="/wiki/Public_address_system" title="Public address system">public address systems</a> and <a href="/wiki/Loudspeaker" title="Loudspeaker">loudspeakers</a>), electric hum is often caused by <a href="/wiki/Electromagnetic_induction" title="Electromagnetic induction">induction</a>. This hum is generated by oscillating <a href="/wiki/Electric_current" title="Electric current">electric currents</a> induced in sensitive (high <a href="/wiki/Gain_(electronics)" title="Gain (electronics)">gain</a> or high impedance) <a href="/wiki/Sound" title="Sound">audio</a> circuitry by the alternating <a href="/wiki/Electromagnetic_field" title="Electromagnetic field">electromagnetic fields</a> emanating from nearby mains-powered devices like power transformers. The audible aspect of this sort of electric hum is produced by <a href="/wiki/Amplifier" title="Amplifier">amplifiers</a> and loudspeakers (note that this is not to be confused with <a href="/wiki/Audio_feedback" title="Audio feedback">acoustic feedback</a>). </p><p>The other major source of hum in audio equipment is shared <a href="/wiki/Electrical_impedance" title="Electrical impedance">impedances</a>; when a heavy current is flowing through a conductor (a <a href="/wiki/Ground_(electricity)" title="Ground (electricity)">ground</a> trace) that a small-signal device is also connected to. All practical conductors will have a finite, if small, resistance, and the small resistance present means that devices using different points on the conductor as a ground reference will be at slightly different potentials. This hum is usually at the second <a href="/wiki/Harmonic" title="Harmonic">harmonic</a> of the power line frequency (100 Hz or 120 Hz), since the heavy ground currents are from <a href="/wiki/AC_to_DC_power_supply" class="mw-redirect" title="AC to DC power supply">AC to DC power supplies</a> that <a href="/wiki/Rectifier" title="Rectifier">rectify</a> the mains waveform. (See also <a href="/wiki/Ground_loop_(electricity)" title="Ground loop (electricity)">ground loop</a>.) </p><p>In <a href="/wiki/Vacuum_tube" title="Vacuum tube">vacuum tube</a> equipment, one potential source of hum is current leakage between the heaters and cathodes of the tubes. Another source is direct emission of electrons from the heater, or magnetic fields produced by the heater. Tubes for critical applications may have the heater circuit powered by direct current to prevent this source of hum.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p><p>Leakage of <a href="/wiki/Video#Analog_video" title="Video">analogue video</a> signals can give rise to hum sounding very similar to mains hum. </p> <div class="mw-heading mw-heading2"><h2 id="Prevention">Prevention</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=2" title="Edit section: Prevention"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>It is often the case that electric hum at a venue is picked up via a ground loop. In this situation, an amplifier and a mixing desk are typically at some distance from one another. The chassis of each item is grounded via the mains earth pin, and is also connected along a different pathway via the conductor of a shielded cable. As these two pathways do not run alongside each other, an electrical circuit in the shape of a loop is formed. The same situation occurs between musical instrument amplifiers on stage and the mixing desk. To fix this, stage equipment often has a "<a href="/wiki/Ground_lift" title="Ground lift">ground lift</a>" switch which breaks the loop. Another solution is to connect the source and destination through a 1:1 <a href="/wiki/Isolation_transformer" title="Isolation transformer">isolation transformer</a>, called variously <i>audio <a href="/wiki/Humbucker" title="Humbucker">humbucker</a></i> or <i>iso coil</i>. An extremely deadly option is to break contact with the ground wire by using an <a href="/wiki/Cheater_plug" class="mw-redirect" title="Cheater plug">AC ground lift adapter</a> or by <a href="/wiki/AC_power_plugs_and_sockets#Earthing_(grounding)" title="AC power plugs and sockets">breaking the earth pin off</a> the power plug used at the mixing deck. Depending on the design and layout of the audio equipment, lethal voltages between the (now isolated) ground at the mixing desk and earth ground can then develop. Any contact between the AC line live terminals and the equipment chassis will energize all the cable shields and interconnected equipment. </p> <div class="mw-heading mw-heading3"><h3 id="Humbucking">Humbucking</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=3" title="Edit section: Humbucking"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Humbucking is a technique of introducing a small amount of line-frequency signal so as to cancel any hum introduced, or otherwise arrange to electrically cancel the effect of induced <a href="/wiki/Utility_frequency" title="Utility frequency">line frequency</a> hum. </p><p>Humbucking is a process in which "hum" that is causing objectionable artifacts, generally in audio or video systems, is reduced. In a <a href="/wiki/Humbucker" title="Humbucker">humbucker</a> electric guitar <a href="/wiki/Pickup_(music_technology)" title="Pickup (music technology)">pickup</a> or microphone, two coils are used instead of one; they are arranged in opposing polarity so that AC hum induced in the two coils will cancel, while still giving a signal for the movement of the guitar strings or diaphragm.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p><p>In certain vacuum-tube radio receivers, a winding on the dynamic speaker field coil was connected in series with the power supply to help cancel any residual hum. </p><p>Some other common applications of this process are: </p> <ul><li>Humbucking transformers or coils used in video systems.</li> <li>Telephone (and other audio) system and computer communications wiring.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Consequences">Consequences</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=4" title="Edit section: Consequences"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="In_music">In music</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=5" title="Edit section: In music"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In musical instruments, hum is usually treated as a nuisance, and various electrical modifications are made to eliminate it. For instance, humbucker pickups on <a href="/wiki/Electric_guitar" title="Electric guitar">electric guitars</a> are designed to reduce the hum.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Sometimes hum is used creatively, for example in <a href="/wiki/Dub_music" title="Dub music">dub</a> and <a href="/wiki/Glitch_(music)" title="Glitch (music)">glitch music</a>. </p> <div class="mw-heading mw-heading4"><h4 id="John_Lennon_demos">John Lennon demos</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=6" title="Edit section: John Lennon demos"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">Main articles: <a href="/wiki/Real_Love_(Beatles_song)" title="Real Love (Beatles song)">Real Love (Beatles song)</a> and <a href="/wiki/Now_and_Then_(Beatles_song)" title="Now and Then (Beatles song)">Now and Then (Beatles song)</a></div> <p>In the late 1970s, former <a href="/wiki/Beatles" class="mw-redirect" title="Beatles">Beatle</a> <a href="/wiki/John_Lennon" title="John Lennon">John Lennon</a> recorded some demo songs at his and <a href="/wiki/Yoko_Ono" title="Yoko Ono">Yoko Ono</a>'s <a href="/wiki/The_Dakota" title="The Dakota">Dakota</a> apartment. These demos did not see any official release at the time, nor were they properly recorded for <i><a href="/wiki/Double_Fantasy" title="Double Fantasy">Double Fantasy</a></i> or its follow-up <i><a href="/wiki/Milk_and_Honey_(album)" title="Milk and Honey (album)">Milk and Honey</a></i>, but they did spread as bootlegs amongst Lennon fans. </p><p>In the mid-1990s, as part of the Beatles anthology series, the three surviving members, <a href="/wiki/Paul_McCartney" title="Paul McCartney">Paul McCartney</a>, <a href="/wiki/George_Harrison" title="George Harrison">George Harrison</a>, and <a href="/wiki/Ringo_Starr" title="Ringo Starr">Ringo Starr</a>, regrouped to record initially incidental music for the albums, but decided to rework some John Lennon demos instead. Several demos were given to McCartney from Ono, the most notable being "<a href="/wiki/Free_as_a_Bird" title="Free as a Bird">Free as a Bird</a>", "Real Love", and "Now and Then". </p><p>Of the demos received, only the aforementioned three were worked on. Of the three, "Real Love" and "Now and Then" were the most difficult to work on as, compared to "Free as a Bird"; both contained a prominent 60-cycle mains hum, as a result of the cheap recording equipment Lennon used to record the demos. While the mains hum was removed from "Real Love",<sup id="cite_ref-f95_4-0" class="reference"><a href="#cite_note-f95-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> it was noticeably louder on "Now and Then", which made it much harder to remove. This, and to a much bigger extent, Harrison's distaste for that particular demo, lead to it being scrapped altogether,<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> although reports circulated in the years since that McCartney was hoping to finish it.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> In 2009, a version of Lennon's demo, supposedly without the mains hum that hampered the Beatles version, appeared as a bootleg. In 2023, the mains hum was finally removed thanks to <a href="/wiki/Peter_Jackson" title="Peter Jackson">Peter Jackson</a>'s <a href="/wiki/Sound_source_separation" class="mw-redirect" title="Sound source separation">sound source separation</a> technology,<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> and the track was released on November 2, 2023.<sup id="cite_ref-announcement_10-0" class="reference"><a href="#cite_note-announcement-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="In_audio_systems">In audio systems</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=7" title="Edit section: In audio systems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Power line hum can be alleviated using a <a href="/wiki/Band-stop_filter" title="Band-stop filter">band-stop filter</a>.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="In_video_systems">In video systems</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=8" title="Edit section: In video systems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In <a href="/wiki/Analog_video" class="mw-redirect" title="Analog video">analog video</a>, mains hum can be seen as hum bars, (bands of slightly different brightness) scrolling vertically up the screen. Broadcast television frame rates are chosen to match the line frequency, to minimize the disturbance these bars cause to the picture. A hum bar can be caused by a ground loop in cables carrying analog video signals,<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> poor power supply smoothing, or magnetic interference with the <a href="/wiki/Cathode-ray_tube" title="Cathode-ray tube">cathode-ray tube</a>. </p> <div class="mw-heading mw-heading3"><h3 id="In_forensics">In forensics</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=9" title="Edit section: In forensics"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Electrical_network_frequency_analysis" title="Electrical network frequency analysis">Electrical network frequency analysis</a></div> <p>Electrical network frequency (ENF) analysis is a <a href="/wiki/Forensic_science" title="Forensic science">forensic</a> technique for validating <a href="/wiki/Audio_recording" class="mw-redirect" title="Audio recording">audio recordings</a> by comparing frequency changes in background mains hum in the recording with long-term high-precision historical records of <a href="/wiki/Mains_frequency" class="mw-redirect" title="Mains frequency">mains frequency</a> changes from a database. In effect the mains hum signal is treated as a time-dependent <a href="/wiki/Digital_watermark" class="mw-redirect" title="Digital watermark">digital watermark</a> that can be used to find when the recording was created, and to help to detect any edits in the sound recording.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=10" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Electromagnetically_induced_acoustic_noise" title="Electromagnetically induced acoustic noise">Electromagnetically induced acoustic noise</a></li> <li><a href="/wiki/Cathode-ray_tube#High-frequency_audible_noise" title="Cathode-ray tube">High frequency noise in CRTs</a></li> <li><a href="/wiki/Valve_amplifier" title="Valve amplifier">Valve amplifier</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mains_hum&action=edit&section=11" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">Robert B. Tomer, <i>Getting the most out of vacuum tubes</i>, Howard W. Sams, Indianapolis, USA 1960, Library of Congress card no. 60-13843, available on the Internet Archive. Chapter 3</span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">Tom Hirst, <i>Electric Guitar Construction</i>, Hal Leonard Corporation, 2003 <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/1-57424-125-7" title="Special:BookSources/1-57424-125-7">1-57424-125-7</a>, page 126</span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFThompson" class="citation journal cs1">Thompson, Art. 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Retrieved 24 June 2005.</span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFRemnick2021" class="citation magazine cs1">Remnick, David (11 October 2021). <a rel="nofollow" class="external text" href="https://www.newyorker.com/magazine/2021/10/18/paul-mccartney-doesnt-really-want-to-stop-the-show">"Paul McCartney Doesn't Really Want to Stop the Show"</a>. <i>The New Yorker</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+New+Yorker&rft.atitle=Paul+McCartney+Doesn%27t+Really+Want+to+Stop+the+Show&rft.date=2021-10-11&rft.aulast=Remnick&rft.aufirst=David&rft_id=https%3A%2F%2Fwww.newyorker.com%2Fmagazine%2F2021%2F10%2F18%2Fpaul-mccartney-doesnt-really-want-to-stop-the-show&rfr_id=info%3Asid%2Fen.wikipedia.org%3AMains+hum" class="Z3988"></span></span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.inthenews.co.uk/money/autocodes/world-cup-teams/angola/mccartney-plans-last-great-song-$1081041.htm">www.inthenews.co.uk</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20070927223245/http://www.inthenews.co.uk/money/autocodes/world-cup-teams/angola/mccartney-plans-last-great-song-$1081041.htm">Archived</a> 27 September 2007 at the <a href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</a></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.bbc.co.uk/programmes/b01n3yf4">"BBC 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title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+New+Yorker&rft.atitle=Paul+McCartney+Doesn%27t+Really+Want+to+Stop+the+Show&rft.date=2021-10-11&rft.aulast=Remnick&rft.aufirst=David&rft_id=https%3A%2F%2Fwww.newyorker.com%2Fmagazine%2F2021%2F10%2F18%2Fpaul-mccartney-doesnt-really-want-to-stop-the-show&rfr_id=info%3Asid%2Fen.wikipedia.org%3AMains+hum" class="Z3988"></span></span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://deadline.com/2023/06/paul-mccartney-john-lennon-beatles-now-and-then-new-record-1235422760/">"Paul McCartney on Upcoming AI-Assisted Beatles Record: "It's All Real and We All Play on It"<span class="cs1-kern-right"></span>"</a>. 22 June 2023.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Paul+McCartney+on+Upcoming+AI-Assisted+Beatles+Record%3A+%22It%27s+All+Real+and+We+All+Play+on+It%22&rft.date=2023-06-22&rft_id=https%3A%2F%2Fdeadline.com%2F2023%2F06%2Fpaul-mccartney-john-lennon-beatles-now-and-then-new-record-1235422760%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AMains+hum" class="Z3988"></span></span> </li> <li id="cite_note-announcement-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-announcement_10-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.thebeatles.com/announcement">"Announcement | The Beatles"</a>. <i><a href="/wiki/TheBeatles.com" class="mw-redirect" title="TheBeatles.com">TheBeatles.com</a></i>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20231026125709/https://www.thebeatles.com/announcement">Archived</a> from the original on 26 October 2023<span class="reference-accessdate">. Retrieved <span class="nowrap">27 October</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=TheBeatles.com&rft.atitle=Announcement+%7C+The+Beatles&rft_id=https%3A%2F%2Fwww.thebeatles.com%2Fannouncement&rfr_id=info%3Asid%2Fen.wikipedia.org%3AMains+hum" class="Z3988"></span></span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFVidyalal,_Rajasree,_and_Sivanand2003" class="citation book cs1">Vidyalal, Rajasree, and Sivanand (2003). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=htD5RbaUmIIC&pg=PA11"><i>Electronics Projects Volume 17 - A simple design of high-quality bandstop filter</i></a>. EFY Enterprises Ltd. p. 11. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/81-88152-10-2" title="Special:BookSources/81-88152-10-2"><bdi>81-88152-10-2</bdi></a><span class="reference-accessdate">. Retrieved <span class="nowrap">2009-08-10</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Electronics+Projects+Volume+17+-+A+simple+design+of+high-quality+bandstop+filter&rft.pages=11&rft.pub=EFY+Enterprises+Ltd&rft.date=2003&rft.isbn=81-88152-10-2&rft.au=Vidyalal%2C+Rajasree%2C+and+Sivanand&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DhtD5RbaUmIIC%26pg%3DPA11&rfr_id=info%3Asid%2Fen.wikipedia.org%3AMains+hum" class="Z3988"></span><span class="cs1-maint citation-comment"><code class="cs1-code">{{<a href="/wiki/Template:Cite_book" title="Template:Cite book">cite book</a>}}</code>: CS1 maint: multiple names: authors list (<a href="/wiki/Category:CS1_maint:_multiple_names:_authors_list" title="Category:CS1 maint: multiple names: authors list">link</a>)</span></span> </li> <li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text">John J. Fay, <i>Encyclopedia of Security Management: Techniques and Technology</i>, Butterworth-Heinemann, 1993, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0750696605" title="Special:BookSources/0750696605">0750696605</a> page 372</span> </li> <li id="cite_note-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-13">^</a></b></span> <span class="reference-text">Cooper, A.J: <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.aes.org/e-lib/browse.cfm?elib=14411">"The electric network frequency (ENF) as an aid to authenticating forensic digital audio recordings – an automated approach"</a>. June 2008.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+electric+network+frequency+%28ENF%29+as+an+aid+to+authenticating+forensic+digital+audio+recordings+%E2%80%93+an+automated+approach&rft.date=2008-06&rft_id=http%3A%2F%2Fwww.aes.org%2Fe-lib%2Fbrowse.cfm%3Felib%3D14411&rfr_id=info%3Asid%2Fen.wikipedia.org%3AMains+hum" class="Z3988"></span>, Conference paper, AES 33rd International Conference, USA (2008)</span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text">Grigoras, C.: <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120307075712/http://www.equinoxjournals.com/IJSLL/article/viewArticle/525">"Digital audio recording analysis – the electric network frequency criterion"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.equinoxjournals.com/IJSLL/article/viewArticle/525">the original</a> on 2012-03-07<span class="reference-accessdate">. Retrieved <span class="nowrap">2010-10-11</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Digital+audio+recording+analysis+%E2%80%93+the+electric+network+frequency+criterion&rft_id=http%3A%2F%2Fwww.equinoxjournals.com%2FIJSLL%2Farticle%2FviewArticle%2F525&rfr_id=info%3Asid%2Fen.wikipedia.org%3AMains+hum" class="Z3988"></span>, International Journal of Speech Language and the Law, vol. 12, no. 1, pp. 63-76 (2005)</span> </li> <li id="cite_note-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-15">^</a></b></span> <span class="reference-text">Mateusz Kajstura, Agata Trawinska, Jacek Hebenstreit. <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.fsijournal.org/article/S0379-0738%2804%2900766-2/abstract">"Application of the Electrical Network Frequency (ENF) Criterion: A case of a digital recording"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Application+of+the+Electrical+Network+Frequency+%28ENF%29+Criterion%3A+A+case+of+a+digital+recording&rft_id=http%3A%2F%2Fwww.fsijournal.org%2Farticle%2FS0379-0738%252804%252900766-2%2Fabstract&rfr_id=info%3Asid%2Fen.wikipedia.org%3AMains+hum" class="Z3988"></span> Forensic Science International, Volume 155, Issue 2, Pages 165-171 (20 December 2005)</span> </li> </ol></div></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?useformat=desktop&type=1x1&usesul3=0" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=Mains_hum&oldid=1281813246">https://en.wikipedia.org/w/index.php?title=Mains_hum&oldid=1281813246</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Help:Category" title="Help:Category">Categories</a>: <ul><li><a href="/wiki/Category:Electrical_phenomena" title="Category:Electrical phenomena">Electrical phenomena</a></li><li><a href="/wiki/Category:Sounds_by_type" title="Category:Sounds by type">Sounds by type</a></li><li><a href="/wiki/Category:Noise" title="Category:Noise">Noise</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:Webarchive_template_wayback_links" title="Category:Webarchive template wayback links">Webarchive template wayback links</a></li><li><a href="/wiki/Category:CS1_maint:_multiple_names:_authors_list" title="Category:CS1 maint: multiple names: authors list">CS1 maint: multiple names: authors list</a></li><li><a href="/wiki/Category:Articles_with_short_description" title="Category:Articles with short description">Articles with short description</a></li><li><a href="/wiki/Category:Short_description_is_different_from_Wikidata" title="Category:Short description is different from Wikidata">Short description is different from Wikidata</a></li><li><a href="/wiki/Category:Articles_needing_additional_references_from_March_2021" title="Category:Articles needing additional references from March 2021">Articles needing additional references from March 2021</a></li><li><a href="/wiki/Category:All_articles_needing_additional_references" title="Category:All articles needing additional references">All articles needing additional references</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 22 March 2025, at 17:22<span class="anonymous-show"> (UTC)</span>.</li> <li id="footer-info-copyright">Text is available under the <a href="/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License" title="Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License">Creative Commons Attribution-ShareAlike 4.0 License</a>; additional terms may apply. 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