Audio Routing

This guide covers everything you need to know about routing audio and MIDI in plugdata, from basic stereo I/O to complex multichannel configurations.

Understanding Audio in Plugdata

Signal Flow

Audio flows through plugdata in this order:

Audio Input

Physical inputs or DAW tracks enter via [adc~] objects

Signal Processing

Audio-rate objects (marked with ~) process signals

Audio Output

Processed audio exits via [dac~] to physical outputs or DAW

Key Concepts:

Sample Rate - Samples per second (44100, 48000, 96000 Hz)
Block Size - Samples processed per cycle (affects latency)
Channels - Separate audio streams (mono=1, stereo=2, etc.)
Signal vs Message - Audio runs at sample rate, messages at block rate

Audio Input with [adc~]

Basic Input

The [adc~] object receives audio from external sources:

[adc~]              # All enabled inputs
  |
[dac~]              # Pass through to output

Channel Selection

Specify which input channels to use:

Stereo Input
Mono Input
Multiple Inputs
Specific Channels

Receive left and right channels:

[adc~ 1 2]        # Channels 1 and 2 (L/R)
  |   |
  |   [*~ 0.5]    # Process right channel
  |   |
[dac~ 1 2]        # Output to L/R

Receive a single channel:

[adc~ 1]          # Channel 1 only
  |
[*~ 2]            # Process
  |
[dac~ 1 2]        # Send to both outputs

Receive multiple discrete channels:

[adc~ 1 2 3 4]    # Four channels
  |  |  |  |
  |  |  |  [*~ 0.8]  # Process channel 4
  |  |  |  |
[dac~ 1 2 3 4]    # Output four channels

Select non-consecutive channels:

[adc~ 1 3 5]      # Channels 1, 3, and 5
  |  |  |
[dac~ 2 4 6]      # Output to different channels

Channel numbers start at 1. Available channels depend on your audio interface configuration.

Monitoring Input Levels

Visualize input levels:

[adc~ 1 2]          # Stereo input
  |   |
  |   [env~]          # Envelope follower
  |     |
  |   [- 100]         # Convert to dB
  |     |
  |   [nbx]           # Display level
  |
[*~ 0]              # Mute (monitoring only)

Audio Output with [dac~]

Basic Output

The [dac~] object sends audio to external destinations:

[osc~ 440]          # Generate tone
  |
[*~ 0.5]            # Volume
  |
[dac~]              # Output to all enabled channels

Stereo Output

Most common configuration:

# Stereo synth voice
[osc~ 440]          # Oscillator
  |
[*~ 0.5]            # Amplitude
  |
  +------+
  |      |
[dac~ 1 2]          # Left and right output

Panning

Distribute mono signal across stereo field:

[osc~ 440]          # Mono source
  |
  +--------+
  |        |
[*~]      [*~]      # Left/right gain
  |        |
[dac~ 1 2]          # Stereo output
  ^
  |
[hsl]               # Pan control (0-1)
  |
[pack 0 0]
  |
[expr $f1; 1-$f1]   # Calculate L/R gains

Or use the ELSE library:

[osc~ 440]
  |
[pan~ 0]            # Pan position -1 to 1
  |   |
[dac~ 1 2]

Multichannel Output

Route to multiple outputs:

# Quad output (4 speakers)
[noise~]            # Noise source
  |
  +-------+-------+-------+
  |       |       |       |
[dac~ 1   2       3       4]
# Front-L Front-R Rear-L Rear-R

Multichannel Patches

Configuring Channels

Set up multichannel I/O:

Standalone Mode

Settings > Audio > Select input/output channels to enable

Plugin Mode

Configure in your DAW:

Set track input/output channel count
Route hardware or virtual channels
Check plugin I/O configuration

Multichannel Processing

Process multiple channels efficiently:

# 8-channel reverb
[adc~ 1 2 3 4 5 6 7 8]      # 8 inputs
  |   |   |   |   |   |   |   |
  |   |   |   |   |   |   |   [freeverb~]  # Reverb each
  |   |   |   |   |   |   |   |
[dac~ 1 2 3 4 5 6 7 8]      # 8 outputs

Matrix Routing

Create flexible routing matrix:

# Simple 4x4 matrix
[adc~ 1 2 3 4]      # 4 inputs
  |   |   |   |
  |   |   |   +---[*~ 0]---+
  |   |   +-------[*~ 0]---+---[+~]---[dac~ 4]
  |   +-----------[*~ 0]---+---[+~]---[dac~ 3]
  +---------------[*~ 1]---+---[+~]---[dac~ 2]
                  [*~ 0]---+---[+~]---[dac~ 1]
                  
# Control with matrix of number boxes or sliders

Use abstractions to create reusable multichannel processors. Pass channel count as argument.

Channel Configuration

Standalone Channel Setup

Input Configuration

Settings > Audio > Input Channels

Enable needed input channels
Disable unused channels to save CPU
Test with [adc~] and [env~]
Check physical connections

Output Configuration

Settings > Audio > Output Channels

Enable output channels for your setup
Match your speaker/monitor configuration
Test with [osc~] to each output

Plugin Channel Setup

In DAW mode:

Set track channel count in DAW
Insert plugdata on multichannel track
Configure routing in patch with [adc~] and [dac~]
Enable channels as needed in DAW mixer

Common Configurations:

Mono - 1 in, 1 out (single instruments)
Stereo - 2 in, 2 out (most common)
Quad - 4 in, 4 out (surround)
Multi - Any configuration for stems/busses

MIDI Routing

MIDI Input

Receive MIDI messages:

Note Messages
Control Change
Pitch Bend
Program Change

Receive note on/off:

[notein]          # Receive notes
  |    |    |
  |    |  [print channel]
  |  [print velocity]  
[print pitch]

Or for specific channel:

[notein 1]        # Channel 1 only

Receive CC messages:

[ctlin]           # All CC messages
  |    |    |
  |    |  [print channel]
  |  [print cc_number]
[print value]

[ctlin 1]         # CC 1 (mod wheel) only

Receive pitch bend:

[bendin]          # Pitch bend
  |    |
  |  [print channel]
[- 8192]          # Center at 0
  |
[/ 8192]          # Normalize to -1 to 1

Receive program changes:

[pgmin]           # Program changes
  |    |
  |  [print channel]
[print program]

MIDI Output

Send MIDI messages:

# Send notes
[makenote 100 500]  # Velocity 100, duration 500ms
  |    |
[noteout 1]         # Send to MIDI channel 1

# Send CC
[pack 0 0]
  |
[ctlout 1]          # CC number, value, channel

# Send pitch bend  
[*  8192]           # Scale
  |
[+ 8192]            # Offset
  |
[bendout 1]         # Channel 1

MIDI to Audio

Convert MIDI to audio signals:

# Simple synth
[notein]            # Receive MIDI
  |    |
  |  [/ 127]        # Normalize velocity
  |    |
[mtof] |
  |    |
[osc~] |
  |    |
  +----+
     |
   [*~]             # Apply velocity
     |
   [*~ 0.5]         # Master volume
     |
   [dac~]

Use [mtof] to convert MIDI note numbers to frequency in Hz.

Managing Latency

Understanding Latency

Total latency comes from:

ADC latency - Analog to digital conversion
Buffer latency - Processing buffer size
DAC latency - Digital to analog conversion
Plugin latency - Additional processing delay

Formula:

Latency (ms) = (Buffer Size / Sample Rate) × 1000

Example: (256 samples / 48000 Hz) × 1000 = 5.33ms

Buffer Size Selection

Choose based on your needs:

Low Latency
Balanced
High Stability

Buffer: 64-128 samplesPros:

Minimal delay (1.5-3ms at 48kHz)
Good for live performance
Real-time MIDI input feels responsive

Cons:

Higher CPU usage
Risk of audio dropouts
May not work on slower systems

Best for:

Live instrument playing
MIDI controllers
Real-time effects

Latency Monitoring

Check current latency:

Statusbar - Displays current latency in ms
Settings - Audio panel shows buffer size
DAW - Check plugin delay compensation settings

Reducing Latency

Decrease Buffer Size

Settings > Audio > Reduce buffer size (if system can handle it)

Optimize Patch

Remove unnecessary processing
Disable unused GUI updates
Use efficient objects

Adjust Sample Rate

Lower sample rate = less CPU, but less frequency response

Use ASIO (Windows)

ASIO drivers typically offer lower latency than DirectSound

Very small buffer sizes may cause audio crackling or dropouts. Increase buffer if you hear glitches.

Advanced Routing Techniques

Send/Return Buses

Create effect sends:

# Main signal
[adc~ 1 2]          # Input
  |   |
  |   +--------[send~ reverb_send]  # Send to reverb
  |   |
[dac~ 1 2]          # Dry output

# Reverb return
[receive~ reverb_send]
  |   |
[freeverb~]         # Reverb effect
  |   |
[*~ 0.3]            # Wet level
  |   |
[dac~ 1 2]          # Add to output

Sidechain Routing

Use one signal to control another:

# Sidechain compression
[adc~ 1]            # Main signal (bass)
  |
[*~]                # VCA
  |
[dac~ 1]
  ^
  |
[- 1]               # Invert
  |
[env~]              # Envelope follower
  |
[adc~ 2]            # Control signal (kick)

Multi-Effect Chains

Route signal through multiple effects:

[adc~ 1 2]
  |   |
[lop~ 2000]         # EQ
  |   |  
[compressor~]       # Dynamics
  |   |
[chorus~]           # Modulation
  |   |
[freeverb~]         # Reverb
  |   |
[dac~ 1 2]

Troubleshooting Audio

No Audio Output

Check:

DSP enabled (power button in statusbar)
Volume not at zero
Correct output device selected
[dac~] connected properly
Audio not muted in DAW (plugin mode)

Audio Crackling

Solutions:

Increase buffer size
Close other applications
Simplify patch
Check CPU meter
Update audio drivers

Wrong Channels

Verify:

Channel numbers in [adc~] and [dac~]
Physical cable connections
Audio interface channel mapping
DAW routing (plugin mode)

High Latency

Fixes:

Reduce buffer size
Use ASIO drivers (Windows)
Close unnecessary programs
Check DAW delay compensation settings

Next Steps

You now understand audio routing in plugdata:

Creating Patches - Build patches with proper audio routing
Using Objects - Learn more audio processing objects
Performance Optimization - Optimize patches for low latency

Getting Started

Core Concepts

User Guide

Objects Reference

Advanced

Resources

​Audio Routing

​Understanding Audio in Plugdata

​Signal Flow

​Audio Input with [adc~]

​Basic Input

​Channel Selection

​Monitoring Input Levels

​Audio Output with [dac~]

​Basic Output

​Stereo Output

​Panning

​Multichannel Output

​Multichannel Patches

​Configuring Channels

​Multichannel Processing

​Matrix Routing

​Channel Configuration

​Standalone Channel Setup

​Plugin Channel Setup

​MIDI Routing

​MIDI Input

​MIDI Output

​MIDI to Audio

​Managing Latency

​Understanding Latency

​Buffer Size Selection

​Latency Monitoring

​Reducing Latency

​Advanced Routing Techniques

​Send/Return Buses

​Sidechain Routing

​Multi-Effect Chains

​Troubleshooting Audio

​Next Steps

Build docs developers (and LLMs) love

Audio Routing

Understanding Audio in Plugdata

Signal Flow

Audio Input with [adc~]

Basic Input

Channel Selection

Monitoring Input Levels

Audio Output with [dac~]

Basic Output

Stereo Output

Panning

Multichannel Output

Multichannel Patches

Configuring Channels

Multichannel Processing

Matrix Routing

Channel Configuration

Standalone Channel Setup

Plugin Channel Setup

MIDI Routing

MIDI Input

MIDI Output

MIDI to Audio

Managing Latency

Understanding Latency

Buffer Size Selection

Latency Monitoring

Reducing Latency

Advanced Routing Techniques

Send/Return Buses

Sidechain Routing

Multi-Effect Chains

Troubleshooting Audio

Next Steps