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<body class="mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject page-Alternative_Noise_Reduction_Techniques rootpage-Alternative_Noise_Reduction_Techniques skin-monobook action-view"><div id="globalWrapper">
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<h1 id="firstHeading" class="firstHeading" lang="en">Alternative Noise Reduction Techniques</h1>
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<div id="bodyContent" class="mw-body-content">
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<div id="siteSub">From Audacity Development Manual</div>
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<div id="jump-to-nav" class="mw-jump">Jump to: <a href="#column-one">navigation</a>, <a href="https://alphamanual.audacityteam.org/man/Alternative_Noise_Reduction_Techniques#searchInput">search</a></div>
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<div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><div class="intro">Audacity's <b>Noise Reduction</b> effect can be used to attenuate <b>constant</b> background noise such as tape hiss, electric fans or hums. It will not work very well for removing talking or music in the background. There are two steps:
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<ul><li>Show Audacity a "noise profile" - a short section of audio containing <b>only the noise to be reduced</b></li>
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<li>Return to the effect to apply the noise profile to all the audio.</div></li></ul>
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<div id="notch"></div>
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<div id="toc" class="toc"><div id="toctitle"><h2>Contents</h2></div>
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<ul>
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<li class="toclevel-1 tocsection-1"><a href="#Notch_Filter"><span class="tocnumber">1</span> <span class="toctext">Notch Filter</span></a></li>
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<li class="toclevel-1 tocsection-2"><a href="#Spectral_Editing"><span class="tocnumber">2</span> <span class="toctext">Spectral Editing</span></a></li>
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<li class="toclevel-1 tocsection-3"><a href="#Noise_Gate"><span class="tocnumber">3</span> <span class="toctext">Noise Gate</span></a>
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<ul>
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<li class="toclevel-2 tocsection-4"><a href="#Nyquist_Noise_Gate_Plugin"><span class="tocnumber">3.1</span> <span class="toctext">Nyquist Noise Gate Plugin</span></a></li>
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</ul>
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</li>
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<h2><span class="mw-headline" id="Notch_Filter"><a href="notch_filter.html" title="Notch Filter">Notch Filter</a></span></h2>
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<p>Suppose you have loaded your audio into Audacity and listened to it, only to be disappointed to find it iss contaminated with a continuous, fairly pure tone of some kind. This is a case where you can get good results using the <a href="notch_filter.html" title="Notch Filter">Notch Filter</a> effect which you will find underneath the divider in the Effect menu.
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</p>
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<div id="spectral"></div>
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<h2><span class="mw-headline" id="Spectral_Editing">Spectral Editing</span></h2>
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<p>Use the <a href="spectral_selection.html#edit" title="Spectral Selection">Spectral Editing</a> tools to identify and eliminate continuous tones or transient noises.
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</p>
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<div id="gate"></div>
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<h2><span class="mw-headline" id="Noise_Gate">Noise Gate</span></h2>
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<p>A <a rel="nofollow" class="external text" href="http://en.wikipedia.org/wiki/Noise_gate">Noise Gate</a> is a type of "audio gate" that is "open" and allows sounds to pass unaltered when the level is above a "threshold" level. When the audio signal is below the threshold level, the gate "closes" and stops, or reduces the signal making it substantially quieter. A Noise Gate does not eliminate noise from a signal but reduces the noise level during the quiet periods between sounds. There are many situations where this can be useful.
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</p>
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<ul><li> When there is very low level noise that is effectively masked by the recorded material, a Noise Gate can lower the noise level during silent parts of the recording where the low level noise would otherwise be apparent.
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<div class="note">Example: Noise Gate can eliminate <a href="dither.html" title="Dither">dither</a> noise that may be evident in silent passages in 16-bit audio files. Be sure in Quality Preferences to enable 32-bit Default Sample Format and to disable "High-quality" dither - more explanation <a rel="nofollow" class="external text" href="https://forum.audacityteam.org/viewtopic.php?f=28&t=38756">here</a>.</div>
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<li> When noise reduction by other methods causes unacceptable degradation of the sound quality, a Noise Gate can reduce the noise level to some extent between sounds without affecting the actual recorded sounds.
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<li> Where there is low level intermittent noise of a similar type to the actual recorded sound (for example, if sound from a distant television or radio is audible during pauses in a speech recording) a Noise Gate can make the pauses more silent.
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<li> A Noise Gate may be used after the Audacity Noise Reduction effect to further reduce the noise level during periods that should be silent.</ul>
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<h3><span class="mw-headline" id="Nyquist_Noise_Gate_Plugin">Nyquist Noise Gate Plugin</span></h3>
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<table style="margin-left:50px">
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<tr>
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<td><a href="https://alphamanual.audacityteam.org/man/File:Noise_Gate.png" class="image" title="Nyquist Noise Gate GUI"><img alt="Nyquist Noise Gate GUI" src="../m/images/9/9e/noise_gate.png" width="400" height="310" /></a>
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</td></tr></table>
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<p>The <a href="noise_gate.html" title="Noise Gate">Noise Gate</a> plugin has a number of features and settings that allow it to be both effective and unobtrusive. One of the most critical settings when using a Noise Gate is to set the <i>Threshold</i> carefully. This plugin provides an analysis tool to assist with setting the threshold level correctly:
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</p>
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<ol><li> Make a selection that is "noise only" and open the Noise Gate effect.</li>
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<li> <span class="menu">Select Function > Analyse Noise Level</span> and make a note of the suggested threshold level.</li>
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<li> Select a section of the audio track that includes both sound and <i>silence</i>.</li>
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<li> Apply the Noise Gate with the following settings: <span class="menu">Select Function > Gate</span> <span class="menu">Level reduction > -100</span>. Listen carefully to the result to check that the noise is being cut and the audio is still present. This effect will probably sound unnatural as the gate is fully closing and producing absolute silence when closed, but it will allow you to easily hear if the threshold level is set correctly. Click CTRL + Z to undo and if necessary adjust the threshold level and retest.</li>
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<li> When you are happy that the threshold level is correct, raise the "Level reduction" setting to the highest setting that produces an acceptable amount of gating (the default level of -12 dB usually works well).</li>
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<li> When you are happy with the settings, apply to the entire song.</li></ol>
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<td width="30px" valign="top" align="center"><img alt="Tip" src="../m/images/d/d7/bulbicon.png" title="Tip" width="32" height="32" />
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</td>
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<td align="left" valign="top"><b>Advanced Tip:</b> By default the Noise Gate will take 1/4 second or 250 milliseconds (ms) to fully open and fully close. In some cases it is desirable to make the gate open faster or more slowly. At the minimum (10 ms) the gate will fully open and close almost instantly as the audio level crosses the threshold. This could cause the gate to 'flutter' or 'snap'. At the maximum
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<p>(1000 ms) the gate will begin to slowly open (fade-in) 1 second before the sound level exceeds the Threshold, and will gradually close (fade-out) after the sound level drops below the Threshold for a period of 1 second. Longer gate times (up to 10 seconds) may be achieved by typing in the text box instead of using the slider.
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<div align="center"><ul id="f_list"><li>This version created on 2025-12-04 - <a href="https://alphamanual.audacityteam.org/man/Alternative_Noise_Reduction_Techniques">Check current version of this page (development Manual)</a></li></ul></div>
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