Once a track has been recorded or programmed, the mix decides how its parts relate to each other. The engineer sets relative levels, pans sounds across the stereo field, shapes their tone with equalisation, controls dynamics with compression and creates depth with reverb and delay. Automation then changes these settings over time, so that a section can lift or a solo can come forward. If the goal had to be summed up in one word, Berklee Online suggests balance.
A jazz lo-fi mix is usually soft and intimate by design. Drums sit relaxed rather than punchy, the bass is warm, chords and melody share the middle, and textures such as crackle stay just audible. Mixing comes before mastering, the final stage that prepares the finished stereo file for release.