nixos-config/modules/system/audio.nix

{ config, lib, pkgs, ... }:

with lib;

let

  ladspaPath = "${pkgs.ladspaPlugins}/lib/ladspa";

  jackScript =
    pkgs.writeShellScriptBin "jack" (lib.fileContents <assets/jack.sh>);

  queueElement = {
    options = {
      plugin = mkOption {
        type = with types; str;
        description = "file name without suffix of the plugin";
      };
      label = mkOption {
        type = with types; str;
        description = "label of the queue element (needs to be correct)";
      };
      control = mkOption {
        type = with types; listOf str;
        description = "parameter of plugin";
      };
    };
  };

  sinkElement = {
    options = {
      name = mkOption {
        type = with types; str;
        description = "name of the sink";
      };
      queue = mkOption {
        type = with types; listOf (submodule queueElement);
        description = "queues";
      };
    };
  };

  cfg = config.system.custom.audio;

in {

  options.system.custom.audio = {
    enable = mkEnableOption "use PluseAudio";
    sinks = mkOption {
      type = with types; listOf (submodule sinkElement);
      description = "list of sinks";
    };
  };

  config = mkIf cfg.enable {

    # add virtual midi module
    # -----------------------
    #boot = {
    #  # to route midi signals
    #  # between bitwig and vcvrack
    #  kernelModules = [ "snd_virmidi" ];
    #  # index=-2  prevents from beeing recognised as the default
    #  #           audio device
    #  # midi_devs limit the number of midi devices.
    #  extraModprobeConfig = "options snd-virmidi index=-2 midi_devs=1";
    #};

    # LADSPA
    # ------
    programs.bash.interactiveShellInit = # sh
      ''
        # set ladspa library path
        # about testing the plugins check analyseplugin command
        export LADSPA_PATH=${ladspaPath}
      '';
    programs.zsh.interactiveShellInit = # sh
      ''
        # set ladspa library path
        # about testing the plugins check analyseplugin command
        export LADSPA_PATH=${ladspaPath}
      '';

    # PulseAudio
    # ----------

    # because of systemWide ensure main user is in audio group
    system.custom.mainUser.extraGroups = [ "audio" ];

    hardware.pulseaudio = {
      enable = true;
      package = pkgs.pulseaudioFull;

      # all in audio group can do audio
      systemWide = true;

      extraConfig = ''

        # automatically switch to newly-connected devices
        load-module module-switch-on-connect

        # http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html
        # https://gavv.github.io/articles/pulseaudio-under-the-hood/#ladspa-plugin-sink
        ${builtins.toString (flip map cfg.sinks (sink: ''
          # ladspa sink : ${sink.name}
          # -------------
          ${builtins.toString (flip imap0 (reverseList sink.queue)
            (index: queua:
              let
                sinkName = suffix: "${sink.name}${builtins.toString suffix}";
                sinkValue = "sink_name=${sinkName index}";
                sinkDescription = "sink_properties=device.description=${
                    sinkName index
                  }-${queua.label}";
                masterValue = if (index == 0) then
                  ""
                else
                  "sink_master=${sinkName (index - 1)}";
                pluginValue = "plugin=${ladspaPath}/${queua.plugin}";
                labelValue = "label=${queua.label}";
                controlValue = "control=${
                    builtins.toString
                    (foldl (a: b: "${a},${b}") (head queua.control)
                      (tail queua.control))
                  }";
              in ''
                # ${sinkName index} : ${queua.label}
                load-module module-ladspa-sink ${sinkValue} ${sinkDescription} ${masterValue} ${pluginValue} ${labelValue} ${controlValue}
              ''))}
        ''))}
      '';
    };

    # Packages needed
    # ---------------
    environment.systemPackages = with pkgs; [

      # Music making
      # ------------
      #jackScript
      #jack2Full
      #patchage
      #zynaddsubfx
      #qjackctl

      alsaUtils

      # LADSPA
      # ------
      ladspaPlugins
      ladspa-sdk

      # PulseAudio control
      # ------------------
      pavucontrol
      lxqt.pavucontrol-qt

    ];

  };

}