Alsa Plugin Framework

Ever want to connect audio plugins to alsa sinks? Well this makes doing that way easier.

Q: What's the point of connecting audio plugins to alsa sinks?

1. A lot of movies have a high dynamic range. You could slap a limiter or compressor on one of your sinks to reduce that dynamic range requiring less manual volume adjustment during playback.

Example Usage

We create our alsa chain in audio_settings.json. This file contains two components. The order field whereby you list the plugins you want (order matters). Then every other key corresponds to a plugin supported in the plugins folder. In the following example you have hpf which stands for high pass filter.

{
  "order": ["hpf", "Eq10"],
  "hpf": {
    "info": "High Pass Filter",
    "alsa_alias": "hpf",
    "settings": {
      "frequency_cutoff": "80"
    },
    "template_path": "/home/pi/audioConfigs/plugins/hpf/hpf.template"
  },

The settings field allows you to edit the cutoff frequency.

After you have input the desired settings run effected.sh to generate the new alsa config and copy it into your home directory. You will then need to restart alsa for the changes to take effect.

Add support for a new LADSPA plugin

Create a new folder in plugins with the name of the ladspa plugin as the folder name. Then place a file called pluginname.template there. This template folder contains the alsa template for this plugin. For example, for hpf we have:

Replace all instances of hpf with your plugin name. Replace controls field with the controls documented for the LADSPA plugin you're adding.

pcm.hpf {
	type ladspa
	slave.pcm $NEXT
	path "/usr/lib/ladspa";
	plugins [{
		label hpf
		input {
			controls [ frequency_cutoff ]
		}
	}]
}

Now add an entry to audio_settings.json and you're good to go.