^This. Here is a brief explanation on crossfeed from Meier Audio. It operates on the simple principle that you hear a little bit of the left channel in your right ear and vice versa when listening through speakers. In practice, it mixes in a very faint, slightly delayed, equalized version of the opposite channel to the left and right channels, respectively. But different from a head-related transfer function (HRTF) which can compress the dynamic range of the source material and degrade sound quality with unnatural tonal resonances, crossfeed is much less destructive to source audio. It does not apply any reverb or other effects that can disturb the fragile nature of audio, but its minimalistic approach creates a contiguous soundfield inside your head. The “Meier” style of crossfeed is already implemented in MPC-HC and Foobar2000 in open source code, which is publicly available and very simple to implement in code. Here is open source code you can reference for implementation.