Complex sentence: In the 1950s, the terms "high fidelity" or "hi-fi" were popularized for equipment and recordings designed for more accurate sound reproduction, while "lo-fi" music aims for "authenticity" over perfect production.
Split into simpler sentences: In the 1950s, the terms "high fidelity" or "hi-fi" were popularized for equipment and recordings which exhibited more accurate sound reproduction. The converse term "lo-fi", doesn't necessarily mean "low fidelity", rather that the production ethic aims for "gritty authenticity" over perfect production.