DeMoD Vox

Power armor voice FX — LV2 (Faust) + Csound instrument for Linux.

Inspired by this song. https://www.youtube.com/watch?v=-S8Kr4NvYJY&list=RDMM&start_radio=1&rv=O_xgVCWPzSM

Released as an open source MIT project since I am still learning. Also want you bastards to make shit like this!!!!

Transforms a microphone input into a sealed-helmet, vox-unit voice. Granular pitch shifting, bass shelf boost, bitcrusher, ring modulator, helmet echo, compressor, and TPDF-dithered output to 16/20/24-bit at a locked 96 kHz sample rate.

Packaged as a Nix flake with NixOS and Home Manager modules for one-command setup with Carla and EasyEffects over PipeWire/JACK.

video

---

⚠ Latency

Total round-trip latency (plugin processing + hardware buffer):

Source	Frames	Time @ 96 kHz
Pitch shifter (Faust ef.transpose, window=2048)	2048	~21 ms
Pitch shifter (Csound PVS, ifftsize=2048)	2048	~21 ms
PipeWire hardware buffer (default quantum=256)	256	~2.7 ms
Total (typical)		~24 ms

Latency is constant at all semitone values, including 0 — the pitch engine always runs. In a DAW, compensate by advancing the recorded output forward by ~21 ms, or use manual plugin delay compensation.

---

I/O Specification (Locked)

Property	Value
Sample rate	96 000 Hz — host must match
Input	32-bit float (LV2 audio port)
Output depth	16-bit default · 20-bit · 24-bit selectable
Channels	Mono in → Mono out

---

Signal Chain

IN (32f, 96 kHz)
  → [Pitch Shift]          0 to −12 semitones  (21 ms latency)
  → [HPF] → [LPF] → [Mid Peak EQ]
  → [Bitcrusher / Downsample]
  → [Ring Modulator]
  → [Helmet Echo]
  → [Bass Boost]           1st-order low shelf
  → [Compressor]
  → [Output Gain]
  → [Hard Clip ±1.0]
  → [TPDF Dither + Word-Length Reduction (16/20/24-bit)]
  → [SR Guard × 1.0 or × 0.0]
  → OUT

---

Files

DeMoD-Vox/
├── flake.nix                        Nix flake — packages, modules, devShell
├── modules/
│   ├── nixos.nix                    NixOS module  (system-wide)
│   └── home-manager.nix             Home Manager module (per-user)
├── easyeffects/
│   └── DeMoD_Vox_input.json         EasyEffects input preset
├── DeMoD_Vox.dsp                    Faust source → LV2 / LADSPA
├── DeMoD_Vox.csd                    Csound source → standalone / csound-lv2
├── LICENSE                          MIT
└── README.md

---

Quick Start — NixOS + Home Manager

1. Add the flake input

In your system flake.nix:

{
  inputs = {
    nixpkgs.url     = "github:NixOS/nixpkgs/nixos-unstable";
    home-manager.url = "github:nix-community/home-manager";
    demod-vox.url   = "github:ALH477/DeMoD-Vox";
  };

  outputs = { self, nixpkgs, home-manager, demod-vox, ... }: {
    nixosConfigurations.mymachine = nixpkgs.lib.nixosSystem {
      modules = [
        ./configuration.nix
        demod-vox.nixosModules.default
        home-manager.nixosModules.home-manager
        {
          home-manager.users.youruser = {
            imports = [ demod-vox.homeManagerModules.default ];
          };
        }
      ];
    };
  };
}

2. Enable in configuration.nix

# System-wide: PipeWire at 96 kHz + JACK + RT priorities + Carla
programs.demod-vox = {
  enable              = true;
  quantum             = 256;      # 2.67 ms @ 96 kHz
  installCarla        = true;
  installEasyEffects  = true;
};

3. Enable in your Home Manager config

# Per-user: LV2_PATH, EasyEffects preset, optional Carla session
programs.demod-vox = {
  enable                    = true;
  installEasyEffectsPreset  = true;
  installCarlaSession       = true;   # pre-loads plugin in Carla
  installCarla              = true;
};

4. Rebuild

sudo nixos-rebuild switch --flake .#mymachine

The plugin is now discoverable by Carla and EasyEffects. PipeWire is running at 96 kHz with JACK compatibility and RT priorities.

---

What the Nix Module Does

NixOS module (programs.demod-vox.enable = true)

What	How
Installs LV2 plugin	environment.systemPackages → /run/current-system/sw/lib/lv2/
Sets LV2_PATH	profileRelativeSessionVariables → includes system + user profile lv2 dirs
PipeWire at 96 kHz	services.pipewire.extraConfig → clock rate, quantum, min/max quantum
JACK compatibility	services.pipewire.jack.enable = true
RT priorities	security.rtkit.enable + security.pam.loginLimits for @audio group
VM settings	vm.swappiness = 10, kernel.timer_migration = 0
Installs Carla	optional — installCarla = true
Installs EasyEffects	optional — preset in /etc/easyeffects/input/

Home Manager module (programs.demod-vox.enable = true)

What	How
LV2 to user profile	home.packages → ~/.nix-profile/lib/lv2/
LV2_PATH session var	home.sessionVariables — covers user + system profile paths
EasyEffects preset	xdg.configFile."easyeffects/input/DeMoD_Vox.json"
Carla session	xdg.configFile."rncbc.org/Carla/DeMoD_Vox.carxs"

---

Manual Build (without Nix)

Faust → LV2

-vec -vs 32 -dfs enables SIMD vectorisation and loop scheduling for lower CPU overhead:

faust2lv2 -srate 96000 -vec -vs 32 -dfs DeMoD_Vox.dsp
cp -r DeMoD_Vox.lv2 ~/.lv2/

# Verify URI (needed for EasyEffects preset):
cat DeMoD_Vox.lv2/manifest.ttl | grep 'lv2:Plugin'

Faust → LADSPA (fallback)

faust2ladspa -srate 96000 -vec -vs 32 DeMoD_Vox.dsp
cp DeMoD_Vox.so ~/.ladspa/

Faust → JACK standalone

faust2jack -srate 96000 -vec -vs 32 DeMoD_Vox.dsp && ./DeMoD_Vox

Csound → JACK (PipeWire compatible)

csound -+rtaudio=jack -+rtmidi=null \
       -odac -iadc -b256 -B512 \
       DeMoD_Vox.csd

At 96 kHz, -b256 = 2.67 ms per period. PipeWire-JACK handles the connection — no separate jackd needed.

Csound → ALSA

csound -+rtaudio=alsa -odac0 -iadc0 \
       -b512 -B2048 DeMoD_Vox.csd

---

Using with Carla

1. Start Carla — it connects to PipeWire-JACK automatically.
2. Add Plugin → scan LV2 → search DeMoD Vox. If it doesn't appear:

   echo $LV2_PATH          # check path is set
   ls $LV2_PATH            # check plugin bundle exists
   cat ~/.lv2/DeMoD_Vox.lv2/manifest.ttl   # check URI

3. Connect your microphone input to the plugin input port in the Carla patchbay.
4. Connect the plugin output to your monitor / recording output.
5. Adjust parameters in the plugin GUI or via OSC automation.

Carla sample rate must be 96000. Set in Carla: Settings → Configure Carla → Engine → Sample Rate → 96000.

---

Using with EasyEffects

EasyEffects applies effects to the system microphone input (or output). DeMoD Vox works as a microphone (input device) effect.

1. Open EasyEffects → Input tab.
2. Click Presets → Import → select the installed DeMoD_Vox.json, or use the system/HM module which installs it automatically.
3. Click Load to apply.
4. The plugin appears in the effects chain. Enable it with the toggle.

If the plugin doesn't appear in the effects list:

# Check LV2_PATH is set
echo $LV2_PATH

# Check EasyEffects can see the plugin
easyeffects --lv2-dump 2>&1 | grep -i demod

# Verify the URI in the preset matches the built plugin
cat ~/.config/easyeffects/input/DeMoD_Vox.json | grep '"lv2#'
cat ~/.lv2/DeMoD_Vox.lv2/manifest.ttl | grep 'a lv2:Plugin'
# Update the URI in DeMoD_Vox.json if they differ.

EasyEffects needs PipeWire. It does not work with standalone JACK. The NixOS module configures this correctly.

---

PipeWire / JACK Manual Configuration

If not using the NixOS module, configure PipeWire manually:

# /etc/pipewire/pipewire.conf.d/92-demod-vox.conf
context.properties = {
    default.clock.rate        = 96000
    default.clock.quantum     = 256
    default.clock.min-quantum = 256
    default.clock.max-quantum = 1024
    default.clock.allowed-rates = [ 96000 ]
}

systemctl --user restart pipewire pipewire-pulse wireplumber
# Verify:
pw-cli info 0 | grep -E 'rate|quantum'

For real-time priorities without the NixOS module:

# /etc/security/limits.d/99-audio.conf
@audio  -  rtprio   99
@audio  -  memlock  unlimited
@audio  -  nice     -20

# Add yourself to the audio group:
sudo usermod -aG audio $USER

---

Development Shell

nix develop github:ALH477/DeMoD-Vox

# Or from a local clone:
git clone https://github.com/ALH477/DeMoD-Vox
cd DeMoD-Vox
nix develop

The dev shell includes: faust, csound, carla, easyeffects, jalv, lv2lint, pkg-config.

# Quick test with jalv (minimal LV2 host):
faust2lv2 -srate 96000 -vec -vs 32 -dfs DeMoD_Vox.dsp
jalv.gtk https://faustlv2.grame.fr/DeMoD_Vox

# Lint the LV2 bundle:
lv2lint -s lv2 https://faustlv2.grame.fr/DeMoD_Vox

# Run Nix build checks:
nix flake check

---

Nix Module Options Reference

NixOS (programs.demod-vox)

Option	Type	Default	Description
enable	bool	false	Enable the module
package	package	flake default	Override the plugin package
sampleRate	int	96000	PipeWire clock rate
quantum	int	256	PipeWire/JACK buffer size (frames)
installCarla	bool	true	Install Carla
installEasyEffects	bool	true	Install EasyEffects + system preset
installCsound	bool	false	Install Csound + runner script

Home Manager (programs.demod-vox)

Option	Type	Default	Description
enable	bool	false	Enable the module
package	package	flake default	Override the plugin package
installEasyEffectsPreset	bool	true	Install preset to ~/.config/easyeffects/input/
installCarla	bool	false	Install Carla to user profile
installEasyEffects	bool	false	Install EasyEffects to user profile
installCsound	bool	false	Install Csound + runner to user profile
installCarlaSession	bool	false	Install Carla rack session with plugin pre-loaded

---

Parameter Reference

Heavy

Parameter	Range	Default	Notes
Pitch Shift	−12–0 st	0	0 = no shift (21 ms latency still applies)
Bass Boost	0–18 dB	0 dB	0 = flat passthrough
Bass Freq	40–400 Hz	120 Hz	Shelf −3 dB point

EQ

Parameter	Range	Default
HPF Freq	20–500 Hz	100 Hz
LPF Freq	1–12 kHz	4.5 kHz
Mid Boost	0–18 dB	6 dB
Mid Freq	500–5000 Hz	2000 Hz
Mid BW	100–4000 Hz	800 Hz

Bitcrusher

Parameter	Range	Default
Bit Depth	2–16	8
Downsample	1–8×	2×
Mix	0–1	0.6

Ring Modulator

Parameter	Range	Default
Carrier Freq	1–800 Hz	60 Hz
Mix	0–1	0.35

Helmet Echo

Parameter	Range	Default
Delay	1–60 ms	10 ms
Mix	0–1	0.22
Feedback	0–0.7	0.15

Compressor

Parameter	Range	Default	Notes
Threshold	−40–0 dBFS	−18 dB
Ratio	1–20:1	8:1
Attack	0.1–80 ms	5 ms
Release	10–500 ms	60 ms

Output

Parameter	Range	Default	Notes
Gain	−12–24 dB	+6 dB	Compressor makeup gain; signals above ±1.0 are hard-clipped
Bit Depth	16 / 20 / 24	16	TPDF dither applied at all depths

---

Troubleshooting

Plugin not found by Carla / EasyEffects

echo $LV2_PATH
ls $(echo $LV2_PATH | tr ':' '\n' | head -1)
# If empty, re-login or: source ~/.nix-profile/etc/profile.d/hm-session-vars.sh

PipeWire not at 96 kHz

pw-cli info 0 | grep rate
# Should show: clock.rate = 96000
# If not: systemctl --user restart wireplumber pipewire pipewire-pulse

Xruns / audio dropout

Increase quantum: programs.demod-vox.quantum = 512 (5.3 ms). Check RT priorities:

chrt -p $(pgrep pipewire)    # should show SCHED_FIFO or SCHED_RR
ulimit -r                    # should be > 0 (rtprio limit)

EasyEffects preset URI mismatch

# Get the actual URI from the built plugin:
cat ~/.lv2/DeMoD_Vox.lv2/manifest.ttl | grep 'a lv2:Plugin' -A2
# Update DeMoD_Vox_input.json: replace the URI in "plugins_order" and the key name

Csound JACK connection fails

pw-jack csound -+rtaudio=jack -odac -iadc -b256 -B512 DeMoD_Vox.csd
# pw-jack wraps Csound in the PipeWire JACK layer explicitly

---

Changelog

Current

• Nix flake added: packages, nixosModules.default, homeManagerModules.default, devShells.default, checks
• NixOS module: PipeWire 96 kHz, JACK compat, RTKit, PAM limits, EasyEffects system preset, Carla
• Home Manager module: LV2_PATH, EasyEffects preset, Carla session file
• EasyEffects preset JSON with three named sub-presets
• Latency improved: Faust 85 ms → 21 ms (window 8192→2048); Csound 42 ms → 21 ms (fftsize 4096→2048)
• Build flags: -vec -vs 32 -dfs added to faust2lv2 call for SIMD vectorisation

Previous

• Hard clip before WLR; TPDF dither fixed (two independent LCGs); compressor ratio wired; bass shelf corrected
• Pitch shift + bass boost added; latency documented
• SR locked to 96 kHz; TPDF dither + word-length reduction output

---

License

MIT — see LICENSE.
Copyright (c) 2026 ALH477