Slo vs Brain.fm: Which Focus Sound App Fits You? (2026)

Slo fits if you want a wordless background you put together yourself, with 200+ recorded sounds, 89 of them free, 22 of those noise-color recordings, and a volume on every layer. Brain.fm fits if you want music chosen for a task, organized around Focus, Sleep, Relaxation and Meditation, with an ADHD-oriented setting included.

The short verdict

You’re at a desk, deciding whether music picked for you beats sound you pick yourself. Slo is the second one: brown noise, rain or a river, each layer set to the volume you want. The full library costs a monthly or yearly subscription or a single lifetime purchase, and 180 sounds play free in a browser with no account. Brain.fm is the first one, with music selected around Focus, Sleep, Relaxation or Meditation, an ADHD-oriented setting, and an adjustable neural-effect level.

Which one suits you comes down to whether you enjoy shaping the sound or would rather name a task and let the service handle it. Neither will guarantee that you concentrate better, sleep better, or manage ADHD better.

Brain.fm’s details here come from its official website and the peer-reviewed paper cited below, both read on July 31, 2026; no head-to-head performance test sits behind this page. Slo is our own product, with figures taken from its app source, version 3.132, on September 14, 2026. Neither app can guarantee better focus.

Slo vs Brain.fm at a glance

Decision	Slo	Brain.fm
What you hear	200+ recorded sounds, 89 of them free: 22 noise-color recordings across seven colors, 11 rain tracks, water, wind, fire and forest	Music and soundscapes made for a selected activity
How you control it	Add any number of layers, set a volume for each, and the app keeps that balance per combination	Choose an activity, session, and available effect settings
Best fit	You know which environmental sounds you prefer	You want the service to provide task-specific music
Browser option	180 sounds free at slonoise.com, no account, 15 to 60 minute timers	Web app
Platform paths verified	iPhone, Android, Mac; browser	Web, iOS, Android, and desktop
Main tradeoff	More manual decisions	Less like a traditional sound mixer
Pricing comparison	Monthly, yearly or one-time lifetime	Check the current Brain.fm plans page

Prices, trials, and entitlements can change by region and channel, so this article does not freeze them into a comparison that will age badly.

What Slo offers

Slo ships 200+ recorded sounds, and 89 of them are free for good. Twenty-two are noise-color recordings across seven colors, including 5 different brown noise tracks, so you can pick the brown that covers the noise in your room. Start with brown noise or pink noise, then add rain, a river or a fire if one sound isn’t enough on its own. The mixer takes any number of layers, holds a volume for each, and remembers the balance for every combination, so tomorrow’s work session starts where today’s left off. Any mix you save can be written to a file and loaded on a second device. The focus timer runs from 15 minutes to 24 hours and fades the sound out over up to 2 minutes. Playback keeps going in the background on iPhone and Android, and each sound stays on the device after its first play, so in the app your mix still works on a train with no signal. The full library is a monthly subscription, a yearly subscription or a one-time lifetime purchase, and 180 sounds play free at slonoise.com with no account.

Set against Brain.fm, Slo is thin in places. There’s no functional music, no ADHD mode, no adaptive or generated audio, no sleep tracking, no guided sessions and nothing spoken.

What Brain.fm offers

Brain.fm describes its product as task-based music for Focus, Sleep, Relaxation, and Meditation. Its official site says the audio uses patented modulation technology, offers thousands of hours of music and natural soundscapes, and runs on web, iOS, Android, and desktop. The focus side includes activity choices and a stronger “neural effect” setting aimed at people with attention difficulties.

Using it looks different from picking a noise color. You say what you’re doing, and the service supplies audio designed around that state. Its current plans page shows paid monthly and annual access after a trial, and the exact terms are worth reading at signup.

What the Brain.fm research does and does not establish

A 2024 paper in Communications Biology tested music with rapid amplitude modulation during a sustained-attention task. The effect differed depending on a listener’s attentional difficulty and on timing, and the paper did not show that everyone got more done. One author worked for Brain.fm, and Brain.fm produced the modulated music used in the study. That doesn’t invalidate the work, though it’s worth knowing when you read a claim built on it.

This is better evidence than a testimonial, and it’s still evidence about one set of experimental conditions. It doesn’t turn Brain.fm into a medical treatment, and it doesn’t promise you’ll focus better on whatever you’re doing today.

The differences that should decide your choice

Ambient layers versus functional music

With Slo you’re choosing ingredients you can name: 5 brown noise tracks, 11 rain tracks, rivers, oceans and fire. With Brain.fm you’re naming a goal and getting music written for it. If a melody pulls your eyes off the page while you read, the non-musical backgrounds are easier to stop noticing. If plain noise leaves you cold, music may hold you better.

Manual control versus guided selection

In Slo you decide which layers belong and how loud each one is, with no cap on how many you stack. That freedom costs you setup, maybe a minute the first time. Brain.fm takes those decisions away by sorting audio into activities and effect levels, which is quicker to start and gives you no say over the individual sounds.

ADHD positioning

Brain.fm markets an ADHD-oriented experience and Slo has nothing like it. Brain.fm’s own FAQ says the product is not a permanent treatment. If you have ADHD, treat either app as one piece of your work environment, and keep your diagnosis, medication and coaching where they are.

Browser and device access

Both have a browser path now, so web access on its own no longer decides anything. Slo plays 180 sounds free in a browser and also runs on iPhone, Android and Mac. Brain.fm lists web, iOS, Android, and desktop. Check the device you’ll actually use, because versions of the same product don’t always carry the same features.

Which one should you choose?

If this sounds like you	Better first test	Why
“I want brown noise and rain at different levels.”	Slo	Any number of layers, each with its own volume
“I want to pick Deep Work and press play.”	Brain.fm	Its catalogue is organized around tasks and states
“Lyrics and melodies disrupt my reading.”	Slo	All 200+ sounds are wordless recordings
“Plain noise bores or irritates me.”	Brain.fm	Functional music offers more musical movement
“I want an ADHD-specific setting.”	Brain.fm	It explicitly provides one; Slo does not
“I want to test without installing an app.”	Either	Slo has 180 free browser sounds; Brain.fm lists a web app

To compare them fairly, run the same kind of task twice, keep the volume comfortable, and note how much you finished and how often you drifted off. How impressive the audio sounded in the first minute tells you very little. Our best sounds for focus guide walks through that in more detail.

Slo focus presets

Compare a deep noise base with moving water

Deep Work Studio is the steadier option. River and Green Noise adds natural movement. Keep the one that becomes less noticeable after work begins.

Deep Work Studio

A steady rumble, a wide ambient sound, and typing quiet enough that you barely catch it.

• Brown Noise 48%
• Deep Focus 32%
• Keyboard Typing 9%

Play this mix View details

River and Green Noise for Focus

Running water with a steady hiss underneath, for a desk where the room keeps interrupting you.

• Green Noise 60%
• River 35%

Play this mix View details

Frequently asked questions

Is Slo a direct Brain.fm replacement?

Only if what you want is a background you put together yourself. Slo holds 200+ recorded sounds, 89 of them free, and gives every layer its own volume. There’s no functional-music engine in it, no patented modulation and no ADHD mode.

Does Brain.fm have stronger scientific evidence than Slo?

Brain.fm has peer-reviewed research about its own audio. The 2024 paper found effects that depended on the condition in a sustained-attention task, which is not the same as a benefit for every listener or every task. Slo makes no comparable claim about neural effects.

Can I use either service in a browser?

Yes. Brain.fm’s official site lists a web app, and Slo plays 180 sounds free at slonoise.com with no account, a volume on each layer and timers of 15, 30 or 60 minutes. What the app and the browser can do is not always the same, so check the feature you actually need.

Which is better for ADHD?

Brain.fm offers an ADHD-specific setting and Slo doesn’t. Brain.fm itself says the product is not a permanent treatment. Think of either one as something that shapes your work environment, and keep it alongside qualified care.

Which is better for studying?

If you’re reading or writing and want nothing with a melody or words in it, Slo may suit you, since all 200+ of its sounds are wordless recordings. Brain.fm may suit you if structured music helps you settle. Try each against silence on the same task, and see our sounds for studying guide.

Official sources checked July 31, 2026

• Brain.fm, official product overview — task categories, modulation settings, library description, and platform availability.
• Brain.fm, official pricing page — current plan structure and trial presentation; prices intentionally omitted here because they change.
• Brain.fm, official ADHD page — ADHD-specific positioning and product description.
• Woods et al. (2024), Rapid modulation in music supports attention in listeners with attentional difficulties — study design, results, and conflict-of-interest disclosure.
• Slo app source, version 3.132 (sound list, timer, fade-out and store products), and the slonoise.com sound catalogue, reviewed September 14, 2026

Related comparisons and guides

• Slo vs Endel
• Best focus sound apps
• Brown, white, and pink noise compared
• Slo vs Noisli

Filip Kowalski is the developer of Slo and writes about sound, sleep, and focus.