White noise has equal energy at every frequency, so it sounds hissy and bright — good at masking sharp, sudden sounds like doors and voices. Pink noise drops 3 dB per octave, matching how our hearing weights loudness, so it sounds even and natural, like steady rain; it is the one most sleep studies use. Brown (red) noise drops 6 dB per octave and rumbles like distant surf or a jet cabin; many people find it the most soothing and the least fatiguing over hours.

How it is made. The browser fills a few seconds of audio with random samples (white), then filters it: pink through a standard 7-pole approximation, brown through a leaky integrator. Rain is pink noise with a band-pass filter and randomly timed soft droplet bursts; ocean is brown noise with a slow swell modulating volume and brightness every 9–12 seconds; wind is filtered noise with a wandering centre frequency; the fan adds a low hum to brown noise. The loops are several seconds long and start at random offsets so nothing sounds repetitive. No sound file is ever downloaded — this card makes no network requests.

Sleep timer. Fades to silence over the final 60 seconds rather than cutting off, and then stops the audio engine so it does not keep the device awake. Phones may pause audio when the screen locks or the browser goes to the background; the lock-screen play button usually resumes it.

Listening safely. Keep it quiet — you should still be able to hear a smoke alarm or a child. Around 50 dB at the pillow (a quiet conversation) is plenty; for babies, keep the speaker across the room, not in the cot, and no louder than a gentle shower. Nothing here is medical advice; persistent insomnia or tinnitus deserves a GP.

Privacy. Your mix, volume and timer choice are saved in this browser's local storage so they are ready next time. Nothing else is stored and nothing is sent anywhere.