Controlling Linear Audio Amplification in Ecasound

Ecasound is a powerful command-line digital audio workstation and multitrack processing tool widely used in Unix-like environments. This article details Ecasound’s built-in chain operator used for controlling linear audio amplification, breaking down its syntax, numerical values, and real-world command-line usage.

The Linear Amplification Operator: -ea

In Ecasound, linear audio amplification is controlled by the built-in chain operator -ea.

Unlike decibel-based volume adjustments that scale logarithmically, linear amplification multiplies the amplitude of the audio samples directly by a specified percentage.

Syntax and Parameters

The operator uses the following basic syntax:

-ea:gain%
  • gain%: A linear scaling percentage applied directly to the sample values.
    • 100: Represents unity gain (\(1.0\times\) multiplier). The audio passes through unmodified.
    • 200: Doubles the sample amplitudes (\(2.0\times\) multiplier), representing an approximate gain of \(+6\text{ dB}\).
    • 50: Halves the sample amplitudes (\(0.5\times\) multiplier), representing an attenuation of approximately \(-6\text{ dB}\).
    • 0: Completely silences the audio signal.

Practical Command Examples

To apply a linear boost to an audio file and save the output to a new file, chain the operator between an input and output stream:

ecasound -i:input.wav -ea:150 -o:output.wav

In this command:

  • -i:input.wav sets the source file.
  • -ea:150 amplifies the audio linearly to 150% of its original level (\(1.5\times\) scale factor).
  • -o:output.wav specifies the destination file.

To attenuate a signal by 25% (scaling the level to 75% of original amplitude) in real-time playback:

ecasound -i:track.mp3 -ea:75 -o:alsa

Linear vs. Decibel Amplification

Ecasound provides two primary built-in volume adjustment operators:

  • -ea (Linear): Best suited for mathematical scaling, envelope shaping, and precise sample multiplication.
  • -eadb (Decibel): Best suited for perceptual mixing and mastering tasks, where level adjustments correspond more naturally to human hearing (e.g., -eadb:3 for a \(+3\text{ dB}\) increase).