On macOS High Sierra and later versions, users can now adjust the render quality of each individual effects unit - both built-in effects and user-configured Audio Unit (AU) plug-ins.
Lower values for render quality will ease CPU load while higher values will increase CPU load.
Built-in effects
For built-in effects, the new render quality setting can be adjusted by clicking the button with the CPU icon which sits below the bypass (i.e. on/off) toggle switch. See the image below:
Audio Unit (AU) plug-ins
For AU plug-ins, the new render quality setting's controls can be found on the editor dialog for the plug-in. See the image below:
