Adjusting Ecasound Operator Parameters in Real-Time

This article explains how to dynamically modify effect and filter parameters during live playback using Ecasound Interactive Mode (EIAM). By navigating audio chains and targeting specific chain operators, users can issue real-time commands to alter values such as volume gain, filter cutoffs, or LADSPA plugin variables without stopping or restarting the audio processing engine.

1. Enter Interactive Mode

To control audio processing interactively, launch Ecasound with the interactive mode flag (-c):

ecasound -c -i input.wav -ea:100 -o alsa

Once the interactive prompt (ecasound ('h' for help)>) appears, start playback:

start

2. Select the Active Chain

Ecasound routes audio through chains. Before modifying an operator, you must select the chain that contains it.

To view existing chains and their status:

c-list

Select your target chain (replace default with your chain's name or number):

c-select default

3. Identify and Select the Operator

Each effect, filter, or plugin attached to a chain is an operator.

List the operators present on the currently selected chain:

cop-list

This returns a numbered list of operators (for example, 1. -ea:100 for an amplify operator). Select the desired operator by its index:

cop-select 1

4. Inspect Operator Parameters

Once the operator is selected, view its configurable parameters:

copp-list

This command outputs the index, name, current value, and valid range for each parameter belonging to the active operator.

5. Modify the Parameter Value

To change a parameter in real-time, select the parameter index and assign a new value.

Method A: Select and Set

Select the parameter by its index:
```
copp-select 1
```
Assign a new numerical value:
```
copp-set 50
```

Method B: Relative Adjustments

To incrementally increase or decrease a value without specifying the exact target:

copp-add 5
copp-add -5

Example Walkthrough

Adjusting a lowpass filter (-efl) frequency on the fly:

ecasound ('h' for help)> c-select default
ecasound ('h' for help)> cop-list
1. -efl:400
ecasound ('h' for help)> cop-select 1
ecasound ('h' for help)> copp-list
1. cutoff-frequency: 400.000000 (range: 1.000000 - 20000.000000)
ecasound ('h' for help)> copp-select 1
ecasound ('h' for help)> copp-set 1200

The cutoff frequency changes to 1200 Hz immediately, with continuous audio output.