Sonic w/ SuperCollider on relatime kernel on NixOS

flake.nix

{
  description = "NixOS configuration with real-time kernel, Sonic Pi, and SuperCollider";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    musnix.url = "github:musnix/musnix";
  };

  outputs = { self, nixpkgs, musnix, ... }@inputs: {
    nixosConfigurations.example-config = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        # Import musnix for real-time kernel and audio optimizations
        musnix.nixosModules.musnix
        {
          # Musnix configuration
          musnix = {
            enable = true;
            kernel.realtime = true; # Enable real-time kernel with CONFIG_PREEMPT_RT
            kernel.packages = nixpkgs.lib.mkDefault nixpkgs.legacyPackages.x86_64-linux.linuxPackages_latest;
            # Optional: Enable ALSA sequencer for MIDI support
            alsaSeq.enable = true;
            # Optional: Enable additional real-time optimizations
            rtirq.enable = true;
          };

          # Enable JACK audio server
          services.jack = {
            jackd.enable = true;
            # Use ALSA backend for JACK
            alsa.enable = true;
            # Ensure JACK is compatible with PulseAudio
            pulseaudio.enable = true;
          };

          # Enable PipeWire for modern audio handling (optional, for compatibility)
          services.pipewire = {
            enable = true;
            alsa.enable = true;
            pulse.enable = true;
            jack.enable = true;
          };

          # Enable real-time kit for low-latency audio
          security.rtkit.enable = true;

          # System packages including Sonic Pi and SuperCollider
          environment.systemPackages = with nixpkgs.legacyPackages.x86_64-linux; [
            sonic-pi
            supercollider
            qjackctl # GUI for controlling JACK
          ];

          # User configuration
          users.users.yourusername = {
            isNormalUser = true;
            extraGroups = [ "wheel" "audio" ]; # Add user to audio group for real-time privileges
          };

          # Kernel parameters for low-latency audio
          boot.kernelParams = [ "threadirqs" ];
          boot.kernel.sysctl = {
            "vm.swappiness" = 10;
            "fs.inotify.max_user_watches" = 524288;
          };

          # PAM limits for audio group (reduce xruns)
          security.pam.loginLimits = [
            { domain = "@audio"; item = "memlock"; type = "-"; value = "unlimited"; }
            { domain = "@audio"; item = "rtprio"; type = "-"; value = "99"; }
            { domain = "@audio"; item = "nofile"; type = "soft"; value = "99999"; }
            { domain = "@audio"; item = "nofile"; type = "hard"; value = "99999"; }
          ];

          # Ensure VST and other plugin paths are set for audio applications
          environment.variables = {
            VST_PATH = "/nix/var/nix/profiles/default/lib/vst:/var/run/current-system/sw/lib/vst:~/.vst";
            LV2_PATH = "/nix/var/nix/profiles/default/lib/lv2:/var/run/current-system/sw/lib/lv2:~/.lv2";
            LADSPA_PATH = "/nix/var/nix/profiles/default/lib/ladspa:/var/run/current-system/sw/lib/ladspa:~/.ladspa";
            DSSI_PATH = "/nix/var/nix/profiles/default/lib/dssi:/var/run/current-system/sw/lib/dssi:~/.dssi";
          };

          # System-wide configuration
          nix.settings.experimental-features = [ "nix-command" "flakes" ];
          system.stateVersion = "24.11"; # Adjust to your NixOS version
        }
      ];
      specialArgs = { inherit inputs; };
    };
  };
}