Ecasound Stereo Panning with the -epp Operator

This article provides an overview of how to control stereo soundstage positioning in Ecasound using the built-in -epp operator. Readers will learn the mechanics of the -epp (stereo pan) preset, its parameter structure, how it processes audio channels from mono to stereo outputs, and practical command-line examples for both static and dynamic spatial placement.

Understanding the -epp Operator

In Ecasound, the -epp chain operator stands for "Stereo Pan." It is a dedicated audio effect designed to balance and position audio streams across two output channels (left and right).

The operator uses a percentage-based scale to determine channel weighting:

• 0: Hard left (full signal to channel 1, channel 2 silenced)
• 50: Center (equal signal level to both channel 1 and channel 2)
• 100: Hard right (full signal to channel 2, channel 1 silenced)

Syntax and Parameters

The basic syntax for the operator is:

-epp:pan_percent

The pan_percent argument accepts floating-point values from 0 to 100. When working with a mono source routing into a stereo destination, Ecasound applies the panning coefficient by attenuating the complementary channel while boosting or preserving the targeted channel's gain level according to standard pan laws.

Command-Line Examples

1. Center Panning a Mono File to Stereo

To route a mono file evenly across a stereo output:

ecasound -i:input_mono.wav -epp:50 -o:output_stereo.wav

2. Hard Panning to the Left or Right

To route the audio entirely to the left speaker:

ecasound -i:input.wav -epp:0 -o:output_left.wav

To position the audio fully to the right speaker:

ecasound -i:input.wav -epp:100 -o:output_right.wav

3. Real-Time Hardware Routing

To read from an ALSA input device, place the sound slightly to the left (30%), and output directly to the speakers in real time:

ecasound -i:alsahw,0,0 -epp:30 -o:alsahw,0,0

Dynamic Modulation with Controllers

The -epp operator parameter can also be attached to dynamic controllers to create automated panning (auto-pan) effects. By combining -epp with an oscillator controller such as -kos, the stereo position can oscillate continuously between the left and right speakers over time:

ecasound -i:input.wav -kos:1,0,100,0.5,0 -epp:50 -o:output_autopan.wav

In this setup, -kos assigns a sine-wave controller to parameter 1 of the subsequent -epp effect, cycling between values 0 and 100 at a rate of 0.5 Hz, creating a smooth, sweeping stereo field effect across the output channels.