Ecasound Built-In Low-Pass Filter Operator

This article provides an overview of the native low-pass filter operators available in Ecasound, a versatile command-line multitrack audio processing tool. Readers will learn which specific built-in operators provide low-pass filtering algorithms, how their parameters function, and how to apply them directly to audio streams using practical command-line examples.

The Primary Low-Pass Operators

In Ecasound, the primary built-in operator for standard low-pass filtering is -efl. Ecasound also provides several specialized variations depending on the desired slope, resonance, and filter characteristics:

• -efl:cutoff_freq: The standard second-order low-pass filter. Frequencies above the specified cutoff frequency are attenuated, reducing high-frequency content while allowing lower frequencies to pass through.
• -ef1:cutoff_freq: A first-order low-pass filter. It provides a gentler roll-off (6 dB per octave) compared to -efl, resulting in a more subtle attenuation of higher frequencies.
• -ef3:cutoff_freq,resonance: A resonant low-pass filter. In addition to the cutoff frequency, it accepts a resonance parameter that accentuates frequencies right around the cutoff point.
• -ef4:cutoff_freq,resonance: An alternative resonant low-pass filter algorithm designed for different sonic characteristics and envelope responses.

Parameter Configuration

The parameters used by these operators include:

• cutoff_freq: Defined in Hertz (Hz). This value determines the threshold where attenuation begins (e.g., 1000 for 1 kHz).
• resonance: Defined as a numeric value typically between 0 and 1 (or higher depending on the specific operator implementation), controlling the peak emphasis at the cutoff frequency.

Usage Example

To apply the standard low-pass filter to an audio file using Ecasound, specify the -efl operator within the processing chain:

ecasound -i input.wav -efl:1200 -o output.wav

In this command, input.wav is filtered so that audio frequencies above 1200 Hz are attenuated before being written to output.wav.

For real-time audio input or interactive session setups, the same operator can be attached to any active audio chain using the same syntax.