

As an example, in Reaper, you can add a reverb effect to a section that you are looping. Then in the Render dialog, enable the “second pass render” option.
That chunk of audio that it renders, will become a perfectly seamless loop in itself. The reverb tail that would have gotten chopped off at the end of that render, will continue on with the start of the render.
At that point, if you didn’t really need the beginning and end of the song, you can have that chunk of the song that seamlessly loops forever, when played on repeat.
https://www.nasa.gov/universe/new-nasa-black-hole-sonifications-with-a-remix/