volume 1.0 is not full. It is as recorded.

That one sentence is most of what goes wrong with a mix, and the intuition runs the other way. A sound effect recorded at −24.6 dB and played at 1.0 is still at −24.6 dB — and with the music bed sitting at −9.9, it is fifteen decibels underneath. Nobody hears a subtle version of it. They hear nothing, and the frame it was meant to punctuate goes by unmarked. Capping volume at 1.0 to be safe is not caution; it is silence.

The engine is free and needs no account. Give it what each file measures and what it is being played at, and every cue is converted through 20 log₁₀ and placed against the bed in decibels. It also reports the three things a timeline cannot show you: the gain a quiet file really needs, which is usually above 1.0 — that the preview clamps there, so the editor plays it quieter than the export does — and that cues landing on the same frame sum, two at −6 dB making −3 rather than −6. Every lane ships a worked example that costs nothing. Writing the report needs credits.