Why do people make noises in bed?

Many primates produce copulation calls, but we have surprisingly little data on what human sex sounds like. I present 34 hours of audio recordings from 2239 authentic sexual episodes shared online, each with one vocalizer (1950 female, 289 male). Both acoustic features and arousal ratings from a perceptual experiment follow an inverted-U curve, revealing the likely time of orgasm. Sexual vocalizations become longer, louder, more high-pitched, voiced, and unpredictable at orgasm in both men and women. Men are not less vocal overall, but women start moaning at an earlier stage; speech or even minimally verbalized exclamations are uncommon. While excessive vocalizing sounds inauthentic to listeners, vocal bursts at peak arousal are ubiquitous and less verbalized than in the build-up phase, suggesting limited volitional control. Human sexual vocalizations likely include both consciously controlled and spontaneous moans of pleasure, perhaps best understood as sounds of liking rather than signals specific to copulation.