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<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width,initial-scale=1,viewport-fit=cover"><link rel="preconnect" href="https://stats.apps.seigler.net/"><style>@font-face{font-family:'Inter Variable';font-style:normal;font-display:swap;font-weight:100 900;src:url(/fonts/inter-latin-wght-normal.woff2) format('woff2-variations');unicode-range:U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD}@font-face{font-family:'Inter Variable';font-style:italic;font-display:swap;font-weight:100 900;src:url(/fonts/inter-latin-wght-italic.woff2) format('woff2-variations');unicode-range:U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD}</style><script defer src="https://stats.apps.seigler.net/script.js" data-website-id="ccb4bd94-2a71-47fe-8eea-d85bf75b7f6d"></script><link rel="me" href="https://github.com/seigler"><link rel="webmention" href="https://webmention.io/joshua.seigler.net/webmention"><title>FFmpeg audio cleanup - joshua.seigler.net</title><meta name="description" content="A script to apply dynamic compression and noise reduction to audio files"><meta name="keywords" content="posts, technical, ffmpeg"><meta property="og:title" content="FFmpeg audio cleanup"><meta property="og:type" content=""><meta property="og:url" content="/posts/ffmpeg-audio-cleanup/"><meta name="twitter:title" content="FFmpeg audio cleanup"><meta name="twitter:description" content="A script to apply dynamic compression and noise reduction to audio files"><meta name="twitter:card" content="summary"><meta name="generator" content="Eleventy v3.1.0"><script type="module" crossorigin src="/assets/main-BcCmWSCK.js"></script><link rel="stylesheet" crossorigin href="/assets/main-MPbmXHLu.css"></head><body data-font="english" data-path="/posts/ffmpeg-audio-cleanup/"><header><nav><div class="nav-row"><div class="nav-home"><a href="/">joshua.seigler.net</a></div></div><div class="nav-categories"><a aria-current="page" href="/posts/">/posts</a> <a href="/about/">/about</a> <a href="/now/">/now</a> <a href="/uses/">/uses</a> <a href="/recipes/">/recipes</a> <a href="/music/">/music</a> <a href="/books/">/books</a> <a href="/links/">/links</a> <a href="/search/">/search</a></div></nav><h1>FFmpeg audio cleanup</h1><div class="header-meta"><span>June 26, 2025</span> <span class="tags"><a class="tag" style="--tagIndex:5" href="/tags/technical/">technical</a> <a class="tag" style="--tagIndex:10" href="/tags/ffmpeg/">ffmpeg</a></span></div></header><header class="toc"></header><main data-pagefind-body="data-pagefind-body"><p>I recently needed to process 20+ phone audio recordings. The files are mp3 recordings in stereo, made in an environment with echoes and noise from fans/heaters.</p><p>Although I could do it easily with <a href="https://tenacityaudio.org/" target="_blank" rel="noopener">Tenacity</a> I didn’t want to use a manual process, since it would take days. So I tried using FFmpeg filters and Bash scripting.</p><p>I found an FFmpeg filter called <a href="https://ffmpeg.org/ffmpeg-filters.html#compand" target="_blank" rel="noopener">compand</a> which lets you map an input decibel range to an output decibel range. I also used the <a href="https://ffmpeg.org/ffmpeg-filters.html#anlmdn" target="_blank" rel="noopener">anlmdn</a> filter to reduce noise, and the <a href="https://ffmpeg.org/ffmpeg-filters.html#highpass" target="_blank" rel="noopener">highpass</a> filter to help with clarity.</p><p>I ran into a couple gotchas.</p><ol><li><code>mpv</code> does something special for audio playback that prevents audio from clipping. <code>vlc</code> plays the file as it is.</li><li>Because the compressor has an attack and decay (which is necessary for things to sound good) it can cause clipping if the volume rises sharply. Applying a <code>delay</code> parameter with half the duration of the attack length fixed this.</li></ol><p>Here is the script:</p><p><code>process-audio.sh</code></p><pre class="language-bash"><code class="language-bash"><span class="token shebang important">#!/bin/bash</span>
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<span class="token keyword">if</span> <span class="token punctuation">[</span> <span class="token string">"<span class="token variable">$#</span>"</span> <span class="token operator">==</span> <span class="token string">"0"</span> <span class="token punctuation">]</span><span class="token punctuation">;</span> <span class="token keyword">then</span>
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<span class="token builtin class-name">echo</span> <span class="token string">"Error: no arguments provided."</span>
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<span class="token builtin class-name">echo</span> <span class="token string">"Usage: <span class="token variable">$0</span> file1 file2 file3 ..."</span>
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<span class="token builtin class-name">echo</span> <span class="token string">"or <span class="token variable">$0</span> *.ext"</span>
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<span class="token builtin class-name">exit</span> <span class="token number">1</span>
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<span class="token keyword">fi</span>
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<span class="token builtin class-name">trap</span> <span class="token string">"exit"</span> INT
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<span class="token keyword">while</span> <span class="token punctuation">[</span> <span class="token string">"<span class="token variable">$#</span>"</span> <span class="token operator">!=</span> <span class="token string">"0"</span> <span class="token punctuation">]</span><span class="token punctuation">;</span> <span class="token keyword">do</span>
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<span class="token assign-left variable">path</span><span class="token operator">=</span><span class="token string">"<span class="token variable">${1<span class="token operator">%</span><span class="token operator">/</span>*}</span>"</span>
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<span class="token assign-left variable">file</span><span class="token operator">=</span><span class="token string">"<span class="token variable">${1<span class="token operator">##</span>*<span class="token operator">/</span>}</span>"</span>
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<span class="token assign-left variable">outfile</span><span class="token operator">=</span><span class="token string">"./normalized--<span class="token variable">$file</span>"</span>
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<span class="token keyword">if</span> <span class="token punctuation">[</span> <span class="token operator">!</span> <span class="token parameter variable">-f</span> <span class="token string">"<span class="token variable">$outfile</span>"</span> <span class="token punctuation">]</span><span class="token punctuation">;</span> <span class="token keyword">then</span>
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<span class="token builtin class-name">echo</span> <span class="token string">"Processing <span class="token variable">$1</span>"</span>
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ffmpeg <span class="token parameter variable">-i</span> <span class="token string">"<span class="token variable">$1</span>"</span> <span class="token parameter variable">-v</span> warning <span class="token parameter variable">-ac</span> <span class="token number">1</span> <span class="token parameter variable">-af</span> <span class="token string">"compand=attacks=0.3:decays=0.3:delay=0.15:points=-80/-300|-45/-25|-27/-15|0/-12|20/-12,anlmdn=s=10,highpass=f=500"</span> <span class="token parameter variable">-threads</span> <span class="token number">4</span> <span class="token string">"<span class="token variable">$outfile</span>"</span>
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<span class="token keyword">else</span>
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<span class="token builtin class-name">echo</span> <span class="token string">"Skipping <span class="token variable">$1</span>, already processed."</span>
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<span class="token keyword">fi</span>
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<span class="token builtin class-name">shift</span>
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<span class="token keyword">done</span>
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</code></pre><p>If this is useful to you please leave a comment or send an email, I would love to hear about it.</p></main><script data-isso="//comments.apps.seigler.net/" src="//comments.apps.seigler.net/js/embed.min.js"></script><section id="isso-thread" data-title=""><noscript>Javascript needs to be activated to view comments.</noscript></section><footer>© Joshua Seigler 2025. - <a rel="me" href="mailto:joshua@seigler.net?subject=Hello">Contact</a> - <a href="/feed.xml">RSS</a> - <a href="/unoffice-hours/">Unoffice Hours</a> - <a href="/webrings/">Webrings</a></footer><div id="effects"></div></body></html> |