# Slo - Sleep & Relax with Brown Noise

> Slo is a minimal sound machine for sleep, focus, and relaxation. The app carries 200+ curated sounds; 180 of them play in the browser at slonoise.com with no download and no account. Available on iOS, Android, and Mac.

**Key features**

- 200+ curated sounds in the app, 180 of them playable in the browser (brown noise, white noise, pink noise, nature sounds)
- Sound mixer with individual volume controls
- Saved mixes that keep playing with the screen off
- Intelligent sleep timer with gentle fade-out
- Brown, white, and pink noise varieties
- Nature sounds: rain, ocean waves, forest, thunderstorm
- Available on iOS, Android, and Mac

**Quick facts**

- Rating: 4.9 stars on the App Store
- Price: Free with optional premium
- Platforms: iOS, Android, Mac

**Sound types**

- Brown Noise: Deep, low-frequency sound ideal for sleep and focus
- White Noise: Equal energy across frequencies, masks distractions
- Pink Noise: Balanced frequency distribution, promotes deep sleep
- Nature Sounds: Rain, ocean waves, forest, thunderstorm, birds
- Mechanical: Fan, air conditioner, airplane cabin

**Use cases**

- Falling asleep faster
- Blocking distracting noises
- Deep focus and concentration
- Meditation and relaxation
- Studying and reading
- Baby sleep

**Detailed feature comparison — Slo vs major competitors**

| Feature | Slo | Calm | Headspace | BetterSleep |
|---------|-----|------|-----------|-------------|
| Sound Library | 201 sounds | Large library | 40+ soundscapes | 300+ sounds |
| Sound Mixer | Yes | No | No | Yes |
| Sleep Timer | Yes | Yes | Yes | Yes |
| Brown Noise | Yes | Yes | Limited | Yes |
| White Noise | Yes | Yes | Yes | Yes |
| Pink Noise | Yes | Yes | Limited | Yes |
| Nature Sounds | Yes | Yes | Yes | Yes |
| Meditation | No | Yes | Yes | Yes |
| Sleep Stories | No | Yes (celebrity) | Yes (sleepcasts) | Yes |
| AI Adaptive | No | No | No | No |
| iOS App | Yes | Yes | Yes | Yes |
| Android App | Yes | Yes | Yes | Yes |
| Mac App | Yes | No | No | No |
| Web App | No | Yes | Yes | No |
| Free Tier | Yes | Limited | Limited | Limited |
| Subscription | Optional premium | $69.99/yr | $69.99/yr | $59.99/yr |

**What makes Slo different**

Slo focuses exclusively on ambient sounds and sound mixing, without the complexity of meditation courses, sleep stories, or fitness content. This focused approach means a simpler interface, faster loading, and sounds curated specifically for quality over quantity.

**Brown noise explained**

Brown noise (also called Brownian noise or red noise) produces a deeper, lower-frequency sound compared to white noise. Research suggests brown noise may help with:

- Falling asleep faster by masking environmental sounds
- Maintaining deeper sleep cycles
- Improving focus and concentration
- Reducing anxiety and stress

**Sound categories in Slo**

1. **Noise**: White noise, pink noise, brown noise
2. **Mechanical**: Fan sound, air conditioner, airplane cabin
3. **Weather**: Gentle rain, heavy rain, rain on window, thunderstorm
4. **Nature**: Ocean waves, forest ambience, birds, creek
5. **Urban**: Coffee shop, library, train

## Links

- [Website](https://slonoise.com): Free browser-based sound mixer and the full guide library
- [iOS / Mac](https://apps.apple.com/us/app/slo-white-noise-sound-machine/id6739538343?pt=126878305&ct=llms-full-txt-en&mt=8): Slo on the App Store
- [Android](https://play.google.com/store/apps/details?id=com.sleep.sounds.noise.rain&referrer=utm_source%3Dslonoise_web%26utm_medium%3Dorganic_web%26utm_campaign%3Dllms-full-txt%26utm_content%3Dllms%26utm_term%3Den): Slo on Google Play
- [Resources](https://slonoise.com/resources/): Guides on sleep, focus, and sound
- [Noise generator](https://slonoise.com/tools/noise-generator/): White, brown, pink and green noise in one free browser player; switch colour while it plays
- [Sleep calculator](https://slonoise.com/tools/sleep-calculator/): bedtime and wake-time ranges from editable cycle length and sleep-onset latency
- [Binaural beats generator](https://slonoise.com/tools/binaural-beats-generator/): two sine tones, one per ear, with a 0.5–40 Hz beat, delta to gamma presets, optional pink, brown or white noise and a fade-out timer; headphones required, evidence stated as inconsistent
- [Privacy Policy](https://slonoise.com/privacy/)
- [Terms of Service](https://slonoise.com/terms/)

## Comparisons

- [Slo vs Calm](https://slonoise.com/resources/slo-vs-calm/)
- [Calm review](https://slonoise.com/resources/calm-review/): worth it for Sleep Stories and guided meditation, poor value for soundscapes
- [Endel review](https://slonoise.com/resources/endel-review/): the adaptive soundscape works; the price is unpublished
- [Slo vs Headspace](https://slonoise.com/resources/slo-vs-headspace/)
- [Slo vs BetterSleep](https://slonoise.com/resources/slo-vs-bettersleep/)
- [Slo vs Noisli](https://slonoise.com/resources/slo-vs-noisli/)
- [Slo vs Dark Noise](https://slonoise.com/resources/slo-vs-dark-noise/)
- [Slo vs myNoise](https://slonoise.com/resources/slo-vs-mynoise/)
- [Slo vs Endel](https://slonoise.com/resources/slo-vs-endel/)
- [Slo vs Brain.fm](https://slonoise.com/resources/slo-vs-brainfm/)
- [Slo vs Noizio](https://slonoise.com/resources/slo-vs-noizio/)
- [Slo vs Portal](https://slonoise.com/resources/slo-vs-portal/)

## Ready-to-play presets

Each URL opens the browser player with the layers and the sleep timer already set — no query string, no setup.

- [Rain sounds for sleeping](https://slonoise.com/play/rain-sounds-for-sleeping/): rain 55%, brown noise 25%, 45-minute timer
- [Ocean sounds for sleeping](https://slonoise.com/play/ocean-sounds-for-sleeping/): ocean 60%, pink noise 20%, all night
- [Pink noise for sleep](https://slonoise.com/play/pink-noise-for-sleep/): pink noise 50%, all night
- [Fan noise for sleeping](https://slonoise.com/play/fan-noise-for-sleeping/): ceiling fan 60%, brown noise 20%, all night
- [White noise for sleeping](https://slonoise.com/play/white-noise-for-sleeping/): white noise 45%, all night
- [Brown noise for sleep](https://slonoise.com/play/brown-noise-for-sleep/): brown noise 50%, all night
- [Thunderstorm sounds for sleeping](https://slonoise.com/play/thunderstorm-sounds-for-sleeping/): heavy rain 55%, thunder 45%, 60-minute timer
- [Green noise for sleep](https://slonoise.com/play/green-noise-for-sleep/): green noise 50%, all night
- [Brown noise for studying](https://slonoise.com/play/brown-noise-for-studying/): brown noise 45%, ambient rain 20%, 90-minute timer
- [Background noise for studying](https://slonoise.com/play/background-noise-for-studying/): cafe 45%, keyboard typing 20%, 90-minute timer
- [White noise for studying](https://slonoise.com/play/white-noise-for-studying/): white noise 45%, 90-minute timer
- [White noise for focus](https://slonoise.com/play/white-noise-for-focus/): white noise 45%, mellow wind 15%, 50-minute timer
- [Brown noise for focus](https://slonoise.com/play/brown-noise-for-focus/): brown noise 45%, mellow wind 15%, 50-minute timer
- [White noise for baby](https://slonoise.com/play/white-noise-for-baby/): white noise 40%, all night, with placement notes
- [Brown noise for ADHD](https://slonoise.com/play/brown-noise-for-adhd/): brown noise 50%, 50-minute timer, published with what the evidence shows
- [Rain and thunder](https://slonoise.com/mix/rain-and-thunder/): rain 55%, thunder 45%

Every preset page carries first-party acoustic measurements of the sounds it plays — loop length, integrated loudness, spectral centroid and band split — measured 2026-09-04.

## Switching from a subscription app

- [Calm alternatives in 2026](https://slonoise.com/resources/calm-alternatives/)
- [Endel alternatives in 2026](https://slonoise.com/resources/endel-alternatives/)

## Tinnitus and sound masking

These pages describe how people use masking sound and what the evidence stops short of. Slo is a player, not a medical device, and none of these pages claims a tinnitus outcome.

- [Sound masking for tinnitus](https://slonoise.com/resources/sound-masking-for-tinnitus/)
- [Why tinnitus is more noticeable at night](https://slonoise.com/resources/tinnitus-worse-at-night/)
- [White noise vs brown noise for tinnitus](https://slonoise.com/resources/white-noise-vs-brown-noise-for-tinnitus/)
- [How to sleep with tinnitus](https://slonoise.com/resources/how-to-sleep-with-tinnitus/)
- [Best tinnitus masking apps in 2026](https://slonoise.com/resources/best-tinnitus-masking-apps-2026/)

## Noise colour guides

- [What is green noise](https://slonoise.com/resources/what-is-green-noise/): where green noise sits against brown and white noise, with the measured band split, and why no standards body defines it
- [What is red noise](https://slonoise.com/resources/what-is-red-noise/): red noise is another name for brown noise, 6 dB per octave; where both names come from, what climate scientists mean by red noise, and how Slo's generator measures
- [Brown noise vs white noise](https://slonoise.com/resources/brown-noise-vs-white-noise/): brown falls about 6 dB per octave and white stays flat, so brown covers rumble and white covers hiss and voices
- [White noise for dogs](https://slonoise.com/resources/white-noise-for-dogs/): which colour masks which trigger, how loud to set it, where to put the speaker, and when a dog needs a vet rather than a louder speaker
- [Brown noise for ADHD](https://slonoise.com/resources/brown-noise-for-adhd/): brown noise itself is untested for ADHD; what the white and pink noise studies and the 2024 meta-analysis found, the small effect size, and safe listening levels

## Sleep situations

- [White noise for babies](https://slonoise.com/resources/white-noise-for-babies/): what the measured decibel study says about speaker distance, what a fader position does and does not mean, and how white, pink and brown differ in a nursery
- [How to sleep with a snoring partner](https://slonoise.com/resources/sleep-with-a-snoring-partner/): why masking a snore needs brown noise running all night rather than a timer, where to put the speaker, and why earplugs cover the peaks a speaker cannot
- [Dog scared of fireworks](https://slonoise.com/resources/dog-scared-of-fireworks/): a plan for fireworks night, from the vet weeks ahead to starting brown noise hours before the first bang, and what no speaker can cover
- [White noise for cats](https://slonoise.com/resources/white-noise-for-cats/): which noise colour covers visitors, carriers, moving house and fireworks, why the level goes lower than for people, and where not to put the speaker