Marek Kowalczyk marekkowalczyk

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Building an 'Automatic Gain Control' with SoX

SoX is a great tool for converting and processing audio. As an engineer working at a radio station I find it especially useful for processing audio files so the volume is even and smooth throughout. A recent use case was preparing news bulletins recorded by a non-technical journalist so they sounded clear and loud for an Amazon Alexa skill.

What is an AGC?

Automatic Gain Control (AGC) is an audio processing technique that is designed to smooth out volume differences between different parts of an audio programme. The majority of radio stations will have a device at their transmitter (for example, an Optimod) that does just that. Parts of the broadcast that are two quiet are boosted and parts that are too loud are atenuated.

For those familiar with audio [compressors

	# Zathura configuration file
	# See man `man zathurarc'

	# Open document in fit-width mode by default
	set adjust-open "best-fit"

	# One page per row by default
	set pages-per-row 1

	#stop at page boundries

	This is free and unencumbered software released into the public domain.

	Anyone is free to copy, modify, publish, use, compile, sell, or
	distribute this software, either in source code form or as a compiled
	binary, for any purpose, commercial or non-commercial, and by any
	means.

	In jurisdictions that recognize copyright laws, the author or authors
	of this software dedicate any and all copyright interest in the
	software to the public domain. We make this dedication for the benefit

	Originall From: Posted 2015-05-29 http://ubwg.net/b/full-list-of-ffmpeg-flags-and-options

	This is the complete list that’s outputted by ffmpeg when running ffmpeg -h full.

	usage: ffmpeg [options] [[infile options] -i infile]… {[outfile options] outfile}…

	Getting help:
	-h — print basic options
	-h long — print more options
	-h full — print all options (including all format and codec specific options, very long)

	# Output a single frame from the video into an image file:
	ffmpeg -i input.mov -ss 00:00:14.435 -vframes 1 out.png

	# Output one image every second, named out1.png, out2.png, out3.png, etc.
	# The %01d dictates that the ordinal number of each output image will be formatted using 1 digits.
	ffmpeg -i input.mov -vf fps=1 out%d.png

	# Output one image every minute, named out001.jpg, out002.jpg, out003.jpg, etc.
	# The %02d dictates that the ordinal number of each output image will be formatted using 2 digits.
	ffmpeg -i input.mov -vf fps=1/60 out%02d.jpg

	<meta name="description" content="{{ if .IsHome }}{{ .Site.Params.description }}{{ else }}{{ .Description }}{{ end }}"/>
	<meta name="robots" content="noodp"/>
	<link rel="canonical" href="{{ .Permalink }}" />

	<!-- Twitter Card -->
	<meta name="twitter:card" content="summary" />
	<meta name="twitter:description" content="{{ if .IsHome }}{{ .Site.Params.description }}{{ else }}{{ .Description }}{{ end }}" />
	<meta name="twitter:title" content="{{ .Title }}{{ if .IsHome }} - {{ .Site.Params.Tagline }}{{ else }} - {{ .Site.Title }}{{ end }}" />
	<meta name="twitter:site" content="{{ .Site.Params.twitter }}" />
	<meta name="twitter:creator" content="{{ .Site.Params.twitter }}" />

	#!/usr/bin/env python3

	# based on https://groups.google.com/d/msg/pandoc-discuss/RUC-tuu_qf0/h-H3RRVt1coJ

	import pandocfilters as pf
	import sys
	import re

	def latex(s):
	return pf.RawBlock('tex', s)

	"""
	Convert YouTube subtitles(vtt) to human readable text.

	Download only subtitles from YouTube with youtube-dl:
	youtube-dl --skip-download --convert-subs vtt <video_url>

	Note that default subtitle format provided by YouTube is ass, which is hard
	to process with simple regex. Luckily youtube-dl can convert ass to vtt, which
	is easier to process.