It is clear that headphone listening and loudspeaker listening are different in the way humans perceive sound. That is due to the distorted in-head localization effect when the sound is reflected in a room rather than directly in the ears. In the latter case, instruments that play the music are perceived directly in the head, and not in an external audio stage.

HPEX, short for "Headphone Experience", is an audio processing tool that can be used to optimize audio files for headphone listening. The application aims to reduce the in-head localization effect as much as possible, while not altering the playback quality.

Unlike other applications of its kind, HPEX does not rely on a Head Related Transfer Function (HRTF) algorithm, which reduces in-head localization while affecting the tonal discoloration. Instead, HPEX adds cross talk, early reflections and low reverb levels to the acoustics, making it sound as if it were played by hi-fi speakers.

HPEX allows batch processing, which means it can handle a large number of input files located in a folder. It ensures compatibility with some of the most popular audio formats (MP3, WAV, FLAC, AIFF, ALAC, DSD).

Once the files are loaded, one can configure the output parameters. There are two main settings users can tamper with, namely the depth and the width of the acoustic stage, which affect the strength of the externalization. While you can experiment with different values, usually the default ones work with all recordings.

HPEX adopts an interesting approach, relying on algorithms that fine-tune the sound field while keeping the tonal discoloration at the minimum. As such, it manages to alter audio files and ensure an engaging listening experience when using headphones