Slo vs Endel (2026): Manual Mixer or Adaptive Audio?

Choose Slo if you want a mix you set yourself and can repeat exactly, layer by layer; choose Endel if you want a Focus, Relax or Sleep soundscape that adapts on its own to signals like time, weather and Apple Watch heart rate.

Disclosure: Slo is our app. Endel facts below come from Endel’s official product and technology pages checked July 31, 2026; our best-fit recommendations are subjective.

The short answer: choose Slo if you want to pick sounds and control their volume yourself. Choose Endel if you want a mode-based soundscape that can adapt to context such as time, weather, light, movement, and—in supported Apple Watch use—heart rate. The choice is manual control versus automated adaptation.

Slo vs Endel at a glance

If you care most about…	Better fit	Why
Choosing exact ambient layers	Slo	Its mixer exposes the sounds and a separate volume control for each layer.
Audio that adapts with minimal input	Endel	Endel changes soundscapes using available context signals.
Trying a preset and then editing it	Slo	Browser presets open into an adjustable mixer.
Switching between intent-based modes	Endel	Focus, Relax, and Sleep are central modes.
Apple Watch heart-rate input	Endel	Endel documents it when the device and permissions support it.

This comparison explains product behavior. It does not validate Endel’s wellness-effect claims or promise that either sound approach will improve focus, relaxation, or sleep.

What is the main difference?

Slo uses a curated-library model. Choose from 151 sounds, open a preset, and set each layer’s volume. Its browser tools include a player, timer, presets, and a mixer. Slo also provides app download paths for iOS, Android, and Mac, without claiming identical features everywhere.

Endel uses an adaptive-system model. You choose an intent such as Focus, Relax, or Sleep; Endel’s system then assembles and changes the soundscape. Its technology page says the available inputs depend on the device and permissions and can include time, weather, light, movement, bedtime, and Apple Watch heart rate.

The important distinction is not “old audio versus AI.” Endel’s own explanation says its sound team designs the rules and musical elements, while the software adapts how those elements unfold.

Manual control versus adaptive control

Slo exposes the ingredients. If you want brown noise under rain with the rain barely audible, you can set that relationship directly. You gain repeatability and clear control, but you must make the choices.

Endel exposes the goal. Pick a mode and let the system respond to the context it can access. You get less setup and more variation, but less direct control over specific sound ingredients.

Avoid turning this into a personality test. Try both workflows during the same kind of task. If changing a layer helps you settle the environment, manual mixing has value. If you keep adjusting instead of working, adaptation may be the better fit.

What “personalized” means in Endel

Endel’s official technology page describes multiple possible inputs, but not every device supplies all of them. For example, Endel documents heart rate for Apple Watch use; weather or time can inform other experiences. Permissions also matter.

The verified claim is narrow: Endel can use Apple Watch heart rate as an input when supported. We did not independently test how a specific heart-rate change alters its soundscape, and we do not generalize the feature to other wearables.

Libraries, presets, and modes

Slo lets you browse discrete sounds and use curated presets as editable starting points. That is useful when you know what texture you want or when a particular frequency balance helps mask a room sound.

Endel does not present itself as a conventional catalog of isolated rain, wind, or noise files. Its product centers on functional modes and adaptive soundscapes. That is more hands-off, but it is not the same as having a manual layer library.

Platforms and pricing

Endel currently lists iOS, Android, Mac, Apple Watch, Apple TV, Vision Pro, Alexa, and web experiences. Slo documents browser sound tools and download paths for iOS, Android, and Mac. Platform lists alone do not prove identical capability across devices for either product.

We removed the old exact annual-price comparison and “trial only” claim. Those are volatile purchase details. Check the current Endel and Slo offer shown in your region when price matters.

Which should you choose?

Choose Slo if:

• You want to select exact sounds and set their relative volume.
• Editable presets are more useful to you than adaptive modes.
• You want to test the mixer in a browser before downloading.

Choose Endel if:

• You want the soundscape to change without manual mixing.
• Focus, Relax, and Sleep modes match how you choose audio.
• Supported context inputs, including Apple Watch heart rate, are part of the appeal.

Frequently asked questions

Is Endel just a playlist app?

No. Endel describes a system in which a sound team designs musical elements and logic, then software adapts the soundscape using the inputs available on a device.

Can Endel use heart-rate data?

Endel documents Apple Watch heart rate as a possible input. Availability depends on device support and permission; this article does not generalize that claim to all wearables.

Does Endel have a manual mixer like Slo?

Endel’s official pages emphasize modes and adaptive soundscapes. We did not find a documented manual layer mixer comparable to Slo’s.

Can I use both in a browser?

Yes. Both document web experiences. Slo’s browser experience specifically includes a player, timer, presets, and a manual mixer.

Official sources checked July 31, 2026

• Endel: product, modes, and platforms
• Endel: technology and context inputs
• Internal verification: Slo statements match the project’s product-facts ledger dated July 31, 2026.

Related guides

• Slo vs Brain.fm
• Best focus sound apps in 2026
• How to use sound mixing
• Best sounds for focus

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