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About this tool
Play calming brown noise, rain, surf or fan hum that holds steady then fades to silence on a timer as you fall asleep.
Sleep Sound Fade Timer plays brown noise, rain, ocean surf or fan hum at a steady level while you fall asleep, then fades it to complete silence over a fade time you set. You choose the curve: a logarithmic fade drops an equal number of decibels each minute, which the ear hears as perfectly even, while linear and S-curve fades feel different in the last few minutes. Everything is synthesised in the browser, so it runs offline and no audio file is downloaded.
Open Sleep Sound Fade Timer on AltFTool — it loads instantly in your browser.
Add your input to the workspace.
Adjust the options until the result looks right.
Copy or download the output and put it to work.
A sudden stop can wake you; the level slides to true silence instead.
Logarithmic matches how hearing works, linear is faster at the end, S-curve is gentlest at both ends.
Sound is generated locally with the Web Audio API, so it works offline and uses no data.
Most people fall asleep within 10 to 20 minutes, so a 30 to 60 minute timer with the last 10 to 15 minutes as a fade covers the whole sleep-onset window. Running sound all night is a personal choice, but a timer avoids it disturbing the lighter sleep stages later in the night.
Because loudness is perceived roughly on a decibel scale, not a linear amplitude scale. A linear fade spends most of its time in the quiet region where changes are barely audible and then seems to disappear at the end, while a logarithmic fade drops an equal number of decibels per minute so each step sounds the same size.
Many people find brown noise easier to sleep to than white noise because its energy falls about 6 dB per octave, removing the harsh high frequencies. Research on noise and sleep quality is mixed and results vary between individuals, so treat it as a comfort aid rather than a treatment.
It may stop. Browsers can suspend audio in a backgrounded or locked tab, so keep the tab in the foreground, or add the page to your home screen and stop the screen from sleeping. On a laptop, sleep mode will also stop playback.