The Arnold section in the Preferences window (Edit > Preferences...) contains global application level settings.

Arnold

Arnold in Main Manu Bar

When enabled, the Arnold plugin menu is added to the application menu bar as a separate entry.

When disabled, the Arnold plugin menu is under the Extensions menu.

Material

Default Material System

The default material system decides whether a Node Material or an old Arnold Material (legacy) is created when creating an Arnold material from the plugin (e.g. Create > Arnold menu in the Material Manager, context menu in the IPR window, etc.).

Render Material Preview

When disabled, no Arnold material previews are rendered in the scene, either Arnold Material or Node Material.

Render Shader Previews

When disabled, no shader previews are rendered in an Arnold Node Material.

Viewport Preview

When disabled, Arnold materials are not displayed in the viewport, either Arnold Material or Node Material.

Default Preview Scene

Select the preview scene displayed when a new Arnold Material is created. Preview scenes have to be located in the application or user material preview folder (e.g. %HOME%\AppData\Roaming\MAXON\Maxon Cinema 4D R25_1FE0824E\library\materialpreview).

Default Shader Preview Scene

Select the preview scene displayed in the Node Editor when a new surface type shader is created. Preview scenes have to be located in the application or user material preview folder (e.g. %HOME%\AppData\Roaming\MAXON\Maxon Cinema 4D R25_1FE0824E\library\materialpreview).

Light

Viewport Preview

When disabled, Arnold lights are not displayed in the viewport.

Textures

Tx Generation

Imager

Default LUT Folder

Select a folder which will be set as the LUT folder by default in a newly created tonemap imager.

Default LUT File

Select a LUT file which will be set by default in a newly created tonemap imager.

Default Color Manager

Enable

When enabled, the selected color manager will be set when a new scene is created or a new render settings is added to an existing scene.

Color Manager

Defines the color manager used in the scene.

default - ACES

legacy

OCIO

Config

sRGB color space (narrow)

Linear sRGB color space

Render color space (linear)

View Color Space

Bake View Color Space Into Output

System

DLL Search Path (Windows)

Third-party Arnold plugins (shader, procedural, volumes) can have DLL dependencies on Windows, which have to be loaded when using the given plugins in Arnold. List folders here which contains those DLL dependencies. Environment variables can be used (e.g. $MY_ENV_VAR).