Spacemixing is the adding of low-volume sonic texturing to audio, usually to alter the listener’s sense of space.
The purpose of spacemixing is to add more sonic texture (including depth) for a different sonic perspective.
There are no formal rules regarding how to spacemix correctly. Adding a little spacemixing, or a lot of meticulous spacemixing (e.g. what spacemixing founder Spirit Wave does) is acceptable.
One major use of the spacemixing technique is to modernize older recordings. Typically, songs are remastered (i.e. modernized by relatively slight shifts in compression, equalization, and so on) in a rather conservative way to mostly retain the purity of the original recording. Spacemixing, however, is typically a natural sculpting of intricate audio effects (basically highly creative remastering) that typically retains the expressive character of the original work.
Spacemixing can also be applied to individual tracks during audio creation, which allows for even more texture.
Spacemixing can be listened to casually in a way in which the listener may be unaware that spacemixing is even happening — although the spatial enhancement is likely always emotionally felt.
With focused listening — e.g. listening at a healthy (but not destructive) volume in a dark room (or such), while using a high-quality sound system — likely strongly reveals the added spatial texture of spacemixing.
Spacemixing may have a tremendous psychedelic effect. If the listener is experiencing a psychedelic mindset, the spacemixing is likely merely interpreted as a boost in the psychedelic effect, so the listener may be unaware that spacemixing has been applied in that case.
The best way to understand what spacemixing does is to listen to the original recording, and then immediately listen to the spacemixed version of that recording, all while sober and both being played on your favorite sound system (which is likely good enough).
The spacemixing technique can be applied as a tribute to the original artistry, as available for your attention at Spirit Wave’s YouTube channel.
If you believe that the word spacemixing has not been stated enough herein, then I hope it suffices to end this on… spacemixing.