Controlling sampling noise

You can control the quality of antialiasing, depth of field and motion blurs using the Render Settings > Sampling properties of the RenderPass.

During rendering, each pixel is split into a grid of pixel samples. The Samples Width and Samples Height properties control how fine the resolution of the grid is. Increasing both these values will result in less jaggy edges, smoother depth of field and motion blurs, but at the cost of rendering time.

Still images without depth of field or motion blur can usually be rendered with a 6x6 sample grid. Production animation may probably require 10x10 or higher.

Tweaking sampling

A few knobs can provide helpful in some circonstances:

Time Jitter

This option enables the sampling pattern to be dependent on the frame number. When rendering large depth of field blurs, you can turn this option off so the noise in the blur doesn't change from a frame to the next (but this can cause disturbing aliasing patterns if the camera moves.)

Motion Blur

This option enables the motion blur sampling. If you want to recreate motion blur from motion vectors in compositing, turn this option off.

Motion Blur Density

This option changes the way the shutter range is sampled. By default, the shutter range is uniformly sampled, resulting in a uniform trail of blur.

Change this option to Trailing if you want the motion blur to appear behind, or to Leading if you want the motion blur to appear in front.

the Uniform setting usually less noisy. Changing to a different setting may require you to increase the Samples Width and Samples Height values.