Built-in Delay and Echo Operators in Ecasound

This article provides an overview of Ecasound's native command-line operators for time-based audio processing. It covers the primary built-in delay operator (-etd) and echo operator (-ete), detailing their specific parameters, how feedback mechanisms are implemented, and practical command-line examples for processing audio files.

The Primary Delay Operators: -etd and -ete

Ecasound provides two primary built-in effect operators for generating time-based delays and echoes without requiring external LADSPA plugins:

  1. -etd (Delay effect): Generates distinct repetitions of an audio signal across fixed intervals without feedback loop decay.
  2. -ete (Echo effect): Creates repeating, decaying repetitions using a feedback loop parameter.

Using the Delay Operator (-etd)

The -etd operator creates a discrete number of delayed copies of the input signal. Its syntax requires four parameters:

-etd:delay_time_msec,surround_mode,number_of_delays,mix_percent
  • delay_time_msec: The interval between delays, expressed in milliseconds.
  • surround_mode: Spatial placement behavior (0 = normal delay, 1 = surround mode where delayed channels are inverted or routed to secondary channels).
  • number_of_delays: The exact number of discrete delayed taps generated (integer).
  • mix_percent: The balance of the wet (delayed) signal relative to the total output (0 to 100).

Example Command:

To apply a 300 ms delay with 3 distinct repetitions at a 40% wet mix:

ecasound -i input.wav -o output.wav -etd:300,0,3,40

Using the Echo Operator (-ete)

For classic echo effects where repetitions fade out gradually, Ecasound uses the -ete operator. This operator introduces feedback into the delay line. Its syntax is:

-ete:delay_time_msec,surround_mode,feedback_percent,mix_percent
  • delay_time_msec: The time between each repeating echo, in milliseconds.
  • surround_mode: Spatial routing (0 for normal stereo/mono preservation, 1 for inverted phase surround).
  • feedback_percent: The amount of the delayed signal fed back into the delay line (0 to 100). Higher values produce longer decaying tails.
  • mix_percent: The percentage of processed wet signal mixed into the final output (0 to 100).

Example Command:

To apply a 250 ms echo with a 50% feedback decay and a 30% wet mix:

ecasound -i input.wav -o output.wav -ete:250,0,50,30

Choosing Between -etd and -ete

  • Use -etd when a precise, finite number of repetitions is needed (such as doubling an instrument or creating a single slapback echo with number_of_delays set to 1).
  • Use -ete when a natural, continuous fade-out is desired, mimicking real-world echoes and reverberant spaces through feedback regeneration.