audio effects in liquidsoap

big balls of mud killer
, in 20 December 2014

Do you ever wish you could apply audio effects like compression, echo, or delay to your liquidsoap stream? Liquidsoap provides several built-in effects as well as an endless range of effects via linux’s plugin audio system LADSPA.

You need to install some packages on your system first. The liquidsoap plugin package is required:

sudo apt-get install liquidsoap-plugin-ladspa

If you are compiling liquidsoap from source, you need to uncomment the line ocaml-ladspa in your PACKAGES file.

Once you have that installed, you can use this command to see what ladspa plugins are available.

$ liquidsoap --list-plugins | grep -i ladspa

At first, you may not have any. Liqudsoap uses all the ladspa plugins it finds on your system. You can install more through additional packages. I recommend these ones to get started.

$ sudo apt-get install ladspa-sdk multimedia-audio-plugins

Run liquidsoap --list-plugins | grep -i ladspa again and you should see many plugins listed.

You can get individual documentation for one plugin by using liquidsoap -h name-of-plugin.

$ liquidsoap -h ladspa.compress
no more csLADSPA plugins

C* Compress - Compressor and saturating limiter by Tim Goetze

Type: (?id:string,?attack:'a,?gain:'b,?measure:int,?mode:int,
where 'a, 'b, 'c, 'd, 'e is either float or ()->float

Category: Source / Sound Processing


 * id : string (default: "")
     Force the value of the source ID.

 * attack : anything that is either float or ()->float (default: 0.)
     attack (0 <= <code>attack</code> <= 1).

 * gain : anything that is either float or ()->float (default: 0.)
     gain (dB) (-12 <= <code>gain</code> <= 24).

 * measure : int (default: 0)
     measure (0 <= <code>measure</code> <= 1).

 * mode : int (default: 1)
     mode (0 <= <code>mode</code> <= 3).

 * release : anything that is either float or ()->float (default: 0.25)
     release (0 <= <code>release</code> <= 1).

 * strength : anything that is either float or ()->float (default: 0.25)
     strength (0 <= <code>strength</code> <= 1).

 * threshold : anything that is either float or ()->float (default: 0.)
     threshold (0 <= <code>threshold</code> <= 1).

 * (unlabeled) : source(audio='#f,video='#g,midi='#h) (default: None)

You are probably pretty overwhelmed right now, like most liquidsoap documentation this looks pretty confusing. But its really just telling you what parameters this plugin accepts. Using it is quite simple, you just set the parameters to what you want and it just returns a new source.

source = ladspa.compress(source, attack = 5.0, gain = 8.0, measure = 1, mode =
1, release = 1.0, strength = 1.0, threshold = 1.0)

The above will give you some pretty loud compression.

I admit this is not the niceest way to tweak effects. It would be really nice if it could just be controlled by knobs or something. Perhaps the parameters could be controlled by telnet commands, but I’m not sure how well that would work.

Plus, there is little documentation about how the plugins actually work. I had to google find the original author of the ladspa.compress plugin’s site where he explains what all the parameters do.

They are not documented well, but liquidsoap comes with quite a few built in effects as well. At least the parameters of these effects are documented.

Right now I am using sky(a multiband compressor), compress(a normal compressor), normalize(a volume normalizer), and limit(a limiter) together. This provides a nice loudness boost to my station.

source = sky(source)
source = compress(source, attack = 5.0, gain = 8.0, knee = 10.0, ratio = 5.0, release = 100.0, threshold = -18.0, rms_window = 0.7)
source = normalize(source, target = -1.0, threshold = -65.0)
source = limit(source, threshold = -0.2, attack = 2.0, release = 25.0, rms_window = 0.02)

I’d like to thank JamesHarrison for sharing his conduit repository, where he has a few good examples of using liquidsoap effects.

Are there any other liquidsoap effects you are interested in using? I honestly can’t imagine using much more than just compression,limiting, etc, for a normal radio station. But maybe there are some more interesting liquidsoap setups out there? Let me know.

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