PipeWire VST Stacks using Carla

📋 PipeWire Audio Guide Series

🔹 You are here: Part 4 of 4 - Professional audio processing with plugins

Complete Series:

PipeWire Setup and Fundamentals - Foundation setup and verification
PipeWire Virtual Devices - Create virtual sinks, sources, and loopbacks
PipeWire PulseAudio Integration - PulseAudio compatibility and application routing
PipeWire VST Stacks using Carla ← Professional audio processing with plugins

Previous: PulseAudio Integration - Application routing and compatibility
Foundation: Setup and Fundamentals - Start here if new
Virtual Devices: Virtual Devices - Required for advanced routing

Prerequisites

Before working with VST plugins in PipeWire, you should complete these prerequisite guides:

PipeWire Setup and Fundamentals - Essential foundation
PipeWire Virtual Devices - Virtual device concepts and implementation
PipeWire PulseAudio Integration - Application routing and configuration

You should have:

PipeWire 1.0.7+ and WirePlumber 0.5.2+ installed and verified
All compatibility layers working (ALSA, JACK, PulseAudio)
Understanding of virtual devices and PulseAudio application routing
Experience with audio processing concepts

What is Carla?

Carla is a fully-featured audio plugin host that acts as a bridge between VST plugins and Linux audio systems. It provides:

VST2/VST3 Support: Load Windows and Linux VST plugins
Multiple Plugin Formats: VST, LV2, LADSPA, AU (on macOS), and internal plugins
JACK Integration: Native JACK support for low-latency audio
PipeWire Compatibility: Works seamlessly with PipeWire’s JACK compatibility layer
Plugin Chains: Create complex effect chains and instrument racks

Installation

Option 1: KXStudio Repository (Recommended)

The KXStudio repository by falktx (Carla’s author) provides the most up-to-date packages with latest features and bug fixes:

# Add KXStudio repository
sudo apt update
sudo apt install gpgv wget

# Download package file
wget https://launchpad.net/~kxstudio-debian/+archive/kxstudio/+files/kxstudio-repos_11.2.0_all.deb

# Install it
sudo dpkg -i kxstudio-repos_11.2.0_all.deb

# Update package lists
sudo apt update

# Install latest Carla from KXStudio
sudo apt install carla carla-data carla-lv2 carla-vst

# Check installation
carla --version

What you get:

Latest stable Carla versions (currently 2.5.9+, with development versions 2.6.0+)
Complete plugin format support (VST2, VST3, LV2, LADSPA, AU)
KXStudio-optimized builds with additional features
Regular updates from the official Carla maintainer

Option 2: Ubuntu Default Repositories

For basic functionality with older but stable versions:

# Ubuntu/Debian default repositories
sudo apt install carla carla-data

# Check installation
carla --version

Verification

# Check installed version
carla --version

# Verify PipeWire compatibility
pw-jack carla --help

# Check available plugin formats
carla-discovery native

References:

VST Plugin Support

Content to be added: VST plugin installation and configuration

Basic Usage

Carla integrates with PipeWire through the pipewire-jack compatibility layer, appearing as JACK clients in the PipeWire audio graph.

Core Workflow

Launch Carla: carla starts and connects to PipeWire via JACK compatibility
Add VST Plugins: Load VST2/VST3 plugins using the “Add Plugin” toolbar button
Create Plugin Stacks: Chain multiple effects/instruments in Rack mode for serial processing
Audio Routing: Carla appears in wpctl status as audio streams for manual or automatic routing

PipeWire Integration

# Launch Carla with explicit JACK compatibility
pw-jack carla

# Monitor Carla's PipeWire presence
wpctl status | grep -i carla

How it works:

Carla as JACK client: Uses PipeWire’s libpipewire-module-jack-tunnel for audio routing
Manual patchbay control: Best approach for VST processing chains with precise signal flow control
Virtual device integration: Can route to/from PipeWire virtual devices for complex audio workflows

Plugin Stack Concept

VST plugins in Carla create processing chains where audio flows through multiple effects sequentially. The entire stack appears to PipeWire as a single audio processing node, allowing complex VST setups to integrate seamlessly with virtual sinks and sources.

References:

Creating VST Processing Chains

This section demonstrates how to create VST processing chains using Carla and integrate them into PipeWire’s audio routing system. We’ll use the practical example from our debugging session of routing Spotify audio through Carla VST processing before it reaches your Schiit Modi DAC.

Architecture Overview

Based on our testing, the most effective approach for VST processing chains uses support.null-audio-sink for better manual control over VST processing connections. The audio flow looks like this:

Spotify → Virtual Null Sink → Monitor Ports → Carla (VST) → Hardware DAC (via patchbay)

Why null sinks for VST workflows: From our debugging session, null sinks provide better fit for what you’re trying to do with cleaner manual routing control for VST processing chains. Unlike loopback devices which rely on WirePlumber’s automatic routing, null sinks give you precise control over the signal flow through your VST stack.

Step 1: Create a Null Sink Virtual Device

Create a support.null-audio-sink device optimized for VST processing workflows:

# ~/.config/pipewire/pipewire.conf.d/11-music-null-sink.conf
context.objects = [
    {
        factory = adapter
        args = {
            factory.name = support.null-audio-sink
            node.name = "music-null-sink"
            node.description = "Music Virtual Sink"
            media.class = Audio/Sink
            audio.position = [ FL FR ]
            # Desktop integration properties for user selection
            device.description = "Music Virtual Sink"
            device.class = "sound"
            device.icon-name = "audio-card"
            node.virtual = false
            # Monitor configuration for VST routing
            monitor.channel-volumes = true
            monitor.passthrough = true
            adapter.auto-port-config = {
                mode = dsp
                monitor = true
                position = preserve
            }
        }
    }
]

Apply the configuration:

systemctl --user restart pipewire

Verify the null sink appears:

wpctl status | grep -i music
# Should show the null sink and its monitor ports

What this creates:

music-null-sink: Virtual sink that applications like Spotify connect to (appears in desktop audio controls)
Monitor ports: music-null-sink:monitor_FL and music-null-sink:monitor_FR for routing to Carla

Step 2: Configure Carla Engine

Launch carla and configure it for PipeWire integration:

Set Audio Driver: Go to Settings > Configure Carla > Engine
Select JACK: Set Audio driver to JACK (uses pipewire-jack compatibility layer)
Choose Process Mode: Select Continuous Rack for serial plugin processing

Alternatively, launch directly in Rack mode:

pw-jack carla-rack

Engine Settings Reference: Based on Carla’s process modes:

Continuous Rack: Plugins process in order, top to bottom (ideal for EQ chains)
Patchbay: Full modular routing (for complex setups)

Step 3: Build Your VST Chain

In Carla’s Rack tab, add your VST plugins:

Add Equalizer: Click “Add Plugin” → Select your EQ VST (e.g., EQual, ReaEQ)
Plugin Order: Arrange plugins from top to bottom in processing order
Configure Settings: Adjust EQ bands, frequencies, and gain as desired

Plugin Chain Example (top to bottom processing order):

High-pass filter (remove low-end rumble)
Parametric EQ (shape frequency response)
Compressor (optional - dynamic control)

Step 4: Audio Routing in Patchbay

Switch to Carla’s Patchbay tab to create the manual connections for your VST processing chain:

Connect Null Sink Monitor to Carla Input

Locate Monitor Ports: Find music-null-sink:monitor_FL and music-null-sink:monitor_FR in the available connections

Connect to Carla: Route monitor outputs to Carla’s audio inputs:

music-null-sink:monitor_FL → Carla:input_FL
music-null-sink:monitor_FR → Carla:input_FR

Verify Signal Flow: Audio flows: Spotify → Null Sink → Monitor → Carla VST processing

Connect Carla Output to Hardware DAC

Locate Carla Outputs: Find Carla’s processed audio outputs

Route to Hardware: Connect directly to your Schiit Modi DAC outputs:

Carla:output_FL → alsa_output.usb-Schiit_Modi_3-00.analog-stereo:playback_FL
Carla:output_FR → alsa_output.usb-Schiit_Modi_3-00.analog-stereo:playback_FR

Save Configuration: Create config directory and save project:
```
mkdir -p ~/.local/share/carla
```
File > Save As → Save as ~/.local/share/carla/spotify_vst_chain.carxp

Connection Pattern (manual VST processing control):

music-null-sink:monitor_FL → Carla:input_FL
music-null-sink:monitor_FR → Carla:input_FR
Carla:output_FL → Schiit_Modi:playback_FL
Carla:output_FR → Schiit_Modi:playback_FR

Why This Approach Works: From our debugging session, this null sink approach provides “better fit for what you’re trying to do” with cleaner manual routing control for VST processing chains. You have precise control over the signal flow through your VST stack and directly to your preferred DAC.

Step 5: Route Spotify to Processing Chain

Critical: Spotify connects via PulseAudio compatibility layer and requires pulse.rules configuration, not WirePlumber stream rules.

Automatic Routing for PulseAudio Applications

Create a PulseAudio routing rule that automatically sends Spotify to your null sink:

# ~/.config/pipewire/pipewire-pulse.conf.d/custom.conf
pulse.rules = [
  {
    matches = [
      { application.name = "Spotify" }
    ]
    actions = {
      update-props = {
        target.object = "music-null-sink"
      }
    }
  }
]

Apply the configuration:

systemctl --user restart pipewire

Why this approach is needed: From our debugging session, applications that connect via pipewire-pulse (like Spotify) bypass WirePlumber’s normal stream routing and require their own pulse.rules configuration.

Audio Flow Verification: The complete processing chain should be:

Spotify → music-null-sink (via pulse.rules)
Null sink monitor → Carla VST processing (manual patchbay connection)
Carla output → Schiit Modi DAC (manual patchbay connection)

Testing the routing: After restart, launch Spotify and verify:

wpctl status | grep -i spotify
# Should show Spotify connected to music-null-sink

Step 6: Autostart Carla Processing

For persistent operation, create a systemd service to auto-load your VST chain:

# ~/.config/systemd/user/carla-vst-chain.service
[Unit]
Description=Carla VST Processing Chain
After=pipewire.service

[Service]
Environment=PIPEWIRE_LINK_PASSIVE=true
Type=exec
ExecStart=/usr/bin/pw-jack carla-rack --no-gui %h/.local/share/carla/spotify_vst_chain.carxp

[Install]
WantedBy=default.target

Enable the service:

systemctl --user enable --now carla-vst-chain.service

Verify the service is working:

# Check service status
systemctl --user status carla-vst-chain.service

# Monitor Carla's connection to PipeWire
wpctl status | grep -i carla

Final Testing: With everything configured, the complete audio chain should be:

Launch Spotify → automatically routes to music-null-sink
Carla loads VST processing chain → processes audio from null sink monitor
Processed audio → routed directly to Schiit Modi DAC
Enjoy enhanced audio with VST processing applied to Spotify

Related guides:

benashby.com

PipeWire VST Stacks using Carla

📋 PipeWire Audio Guide Series

Complete Series:

Navigation:

Prerequisites

What is Carla?

Installation

Option 1: KXStudio Repository (Recommended)

Option 2: Ubuntu Default Repositories

Verification

VST Plugin Support

Basic Usage

Core Workflow

PipeWire Integration

Plugin Stack Concept

Creating VST Processing Chains

Architecture Overview

Step 1: Create a Null Sink Virtual Device

Step 2: Configure Carla Engine

Step 3: Build Your VST Chain

Step 4: Audio Routing in Patchbay

Connect Null Sink Monitor to Carla Input

Connect Carla Output to Hardware DAC

Step 5: Route Spotify to Processing Chain

Automatic Routing for PulseAudio Applications

Step 6: Autostart Carla Processing