Sub-bass rumble
Energy below 30–40 Hz is rarely audible but consumes significant headroom. It comes from mic handling noise, HVAC rumble, or sub-octave content from synths. A high-pass filter at 20–30 Hz on the master (or per-track at appropriate frequencies) removes it without affecting the audible mix.
Low-end extension
Conversely, a mix lacking low-end energy reads as "thin" or "cold". PRISM detects this by measuring sub-bass energy against genre thresholds. Hip-hop and electronic music need substantial sub-bass presence. If your mix is thin, check that your bass elements have actual sub content — not just low-mids.
Synthesis vs. sampling
Sampled kicks often have built-in sub that varies by sample. If PRISM flags low sub energy, check your kick sample — some samples are intentionally "clicky" with no sub. You may need to layer a sub-bass sine under the kick or use a synth bass that extends below 60 Hz.
To fix this frequency problem, here are the tools PRISM producers reach for most — each picked for this specific case, not a generic list.