Audio Phase Correlation in Ecasound

This article examines audio phase correlation capabilities in Ecasound, addressing whether the multitrack audio processing software includes a native operator for phase measurement. It outlines the scope and limits of Ecasound's built-in audio analysis operators and explains how to integrate external LADSPA plugins to calculate and monitor phase correlation within an Ecasound processing chain.

Ecasound does not feature a dedicated built-in operator specifically designed to calculate and display audio phase correlation. While Ecasound includes several native audio analysis and diagnostics tools, none of them compute inter-channel phase relationships or cross-correlation coefficients.

The built-in analysis operators provided natively in Ecasound are:

• -ev (Analyze audio energy): Calculates and prints peak and Root Mean Square (RMS) energy levels in decibels across channels over the entire duration of a stream.
• -evp (Analyze peak audio energy): Focuses solely on detecting and printing the maximum peak amplitude levels for the processed audio.

Because -ev and -evp evaluate audio channels independently to determine amplitude metrics, they cannot measure phase alignment, phase cancellation, or stereo width between stereo pairs.

To calculate and monitor phase correlation using Ecasound, you must use its built-in LADSPA host operator:

• -el:plugin_name,param1,param2,...: Loads a LADSPA plugin by its unique label.
• -eli:plugin_id,param1,param2,...: Loads a LADSPA plugin using its numeric identifier.

Linux audio environments supply LADSPA-compatible correlation meters (such as those found in the Steve Harris plugin collection or LADSPA analysis packages) that measure inter-channel phase differences from -1.0 (fully out of phase) to +1.0 (fully mono/in phase).

To analyze phase correlation on a stereo file using an external LADSPA correlation meter through Ecasound, insert the plugin into the signal chain and send the output to the null device:

ecasound -i input_stereo.wav -el:correlation_meter -o null

Alternatively, interactive and visual terminal monitoring can be performed by routing Ecasound outputs through dedicated command-line utilities such as ecasignalview for level diagnostics or piping audio to external modular analysis tools like JACK-based phase scopes.