"White noise" gets used as a catch-all for any background sound that isn't music, which is roughly as precise as calling every task app "a Todoist alternative." They're not interchangeable, and picking the wrong one for what you're actually doing is a large part of why "I tried background noise and it didn't help" is such a common complaint.
White Noise: Flat and Even, Best at Masking
True white noise has equal energy across every audible frequency, which is what gives it that flat hiss, closer to static than to anything natural. Its actual job is masking: it evens out sudden, unpredictable sounds (a door, a conversation two desks over) by keeping the background at a constant level, so the sudden sound isn't as jarring against silence.
Pick white noise if your environment has unpredictable noise you need masked, an open office, a shared apartment, a street-facing window.
Brown Noise: Deeper, Heavier on Low Frequencies
Brown noise (sometimes called red noise) shifts the energy toward lower frequencies, producing something closer to a deep rumble, like distant thunder or a low waterfall, than white noise's flat hiss. Anecdotally, a lot of people who find white noise too sharp or fatiguing over long sessions prefer brown noise for exactly that reason: it's less piercing at the same volume.
Pick brown noise if white noise feels harsh to you, or you're running long sessions where a softer, deeper sound is easier to sit with for hours.
Pink Noise: Between the Two
Pink noise sits between white and brown: more low-frequency energy than white noise, less than brown, often described as sounding like steady rainfall. Some sleep research has looked at pink noise specifically for improving deep sleep quality, though the evidence for a focus benefit specifically is thinner and more mixed than the sleep research. Worth trying, not worth treating as proven.
Pick pink noise if you want something between white noise's edge and brown noise's rumble, or you're also using it to wind down, not just to focus.
Rain and Nature Sounds: Texture Over Masking
Rain, waves, and forest ambience aren't flat noise at all, they have real texture and variation, which is exactly what makes them pleasant and exactly why they're worse at pure masking than white or brown noise. A sudden change in the rain's intensity is still a texture change your brain can notice, just a gentler one than a door slamming.
Pick rain or nature sounds if you find flat noise sterile or unpleasant and you're not fighting genuinely unpredictable background noise.
What Doesn't Belong on This List: Lo-fi and Licensed Music
Lo-fi playlists get lumped in with focus sounds constantly, but music (even instrumental, low-key music) engages language and pattern-recognition parts of the brain in a way flat noise doesn't, which is why it helps some people and actively distracts others, especially on tasks involving reading or writing. It's also a licensing problem for any app that wants to include it, which is part of why it's not on Focus Mode's roadmap at all.
What's Actually Shipping First in Focus Mode
I'm adding a small set to start: white noise, brown noise, and rain. Not a full library like Endel or Noisli offer, three options chosen because they cover masking, a gentler alternative, and a natural-texture option, without turning Focus Mode into an ambient sound app that happens to have a task list attached.
The Honest Take
None of these are universally "the best" background sound, and the research on background noise and focus is genuinely mixed depending on the task, the environment, and the person. The only real way to know which one helps you is running the same kind of work with each for a week and noticing which one you stop consciously hearing, which is usually the sign it's actually working.