How to Build an Ecasound Stem Mixing Template

This guide explains how to design a modular stem mixing template using Ecasound chainsetups. By taking advantage of Ecasound’s lightweight routing engine, chain operators, and loop devices, you can group individual audio tracks into dedicated submixes—such as drums, bass, instruments, and vocals—apply bus-level processing, and sum them to a final stereo master without the overhead of a graphical digital audio workstation.

Core Concepts of Ecasound Routing

Ecasound structures audio processing using chains, inputs, outputs, and operators. To construct a stem mixing workflow, you must route multiple chains into intermediate mixing buses using virtual loop devices (loop,id).

Chains (-a:chain_name): Independent signal paths.
Audio Inputs (-i:source): Audio files, JACK ports, or loop devices feeding into chains.
Audio Outputs (-o:target): Soundcards, output files, or loop devices receiving audio from chains.
Loop Devices (loop,N): Internal buffers that allow the output of one or more chains to act as the input for another chain, functioning exactly like a bus or aux track.

Designing the Routing Architecture

A standard stem mixing template routes individual tracks into four primary stems, which then sum to a master output:

Track Chains: Play individual audio files, apply track-level pan/gain, and output to a stem loop.
Stem Chains: Receive input from the stem loop, apply group effects (compression, EQ), and output to the master loop.
Master Chain: Receives audio from the master loop, applies final limiting/metering, and routes to hardware playback or a bounce file.

Constructing the Chainsetup Template

You can define your template in an Ecasound Chainsetup (.ecs) file or as an executable shell script using standard Ecasound arguments. Below is a complete, scalable template structure.

1. Define Track Inputs and Assign to Stems

Group individual audio tracks into specific stems using designated loop devices (loop,1 for Drums, loop,2 for Music, loop,3 for Vocals):

# --- DRUM TRACKS -> DRUM STEM (loop,1) ---
-a:kick   -i:kick.wav   -ea:100 -epp:50 -o:loop,1
-a:snare  -i:snare.wav  -ea:90  -epp:50 -o:loop,1
-a:hihat  -i:hihat.wav  -ea:70  -epp:35 -o:loop,1

# --- MUSIC TRACKS -> MUSIC STEM (loop,2) ---
-a:bass   -i:bass.wav   -ea:95  -epp:50 -o:loop,2
-a:guitar -i:guitar.wav -ea:80  -epp:20 -o:loop,2
-a:keys   -i:keys.wav   -ea:75  -epp:80 -o:loop,2

# --- VOCAL TRACKS -> VOCAL STEM (loop,3) ---
-a:lead_vox -i:lead.wav -ea:100 -epp:50 -o:loop,3
-a:bg_vox   -i:harm.wav -ea:70  -epp:65 -o:loop,3

2. Configure Stem Processing and Sum to Master

Create chains that capture the loop inputs, apply bus processing (such as LADSPA plugins or internal gain adjustments), and forward the signals to a master loop (loop,99):

# --- DRUM BUS ---
-a:stem_drums -i:loop,1 -ea:100 -o:loop,99

# --- MUSIC BUS ---
-a:stem_music -i:loop,2 -ea:90  -o:loop,99

# --- VOCAL BUS ---
-a:stem_vox   -i:loop,3 -ea:105 -o:loop,99

3. Master Output Configuration

Take the summed signal from loop,99, apply final limiting or monitoring levels, and direct it to your audio interface or a stereo bounce file:

# --- MASTER STEREO BUS ---
-a:master -i:loop,99 -ea:100 -o:alsa
# Alternatively, bounce to disk:
# -a:master -i:loop,99 -ea:100 -o:final_mix.wav

Executing and Interacting with the Template

Save your configuration in a text file named mix_template.ecp (or as a shell script). Run Ecasound in interactive mode (-c) to control the mix in real time:

ecasound -c -f:s16_le,2,44100 \
  -a:kick -i:kick.wav -o:loop,1 \
  -a:snare -i:snare.wav -o:loop,1 \
  -a:stem_drums -i:loop,1 -ea:100 -o:loop,99 \
  -a:master -i:loop,99 -o:alsa

While running in interactive mode, you can dynamically modify levels, mute stems, or adjust stereo panning using standard Ecasound commands:

c-select stem_drums followed by c-set-parameter 1 80 to adjust stem volume.
c-mute stem_vox to check the instrumental balance.
start and stop to control playback across all synchronized chains.