@dover and @testpilot are not wrong.
DD motors are controlled by computer speed measurement and are constantly being speeded up and slowed down to achieve the designer's aim of a perfectly stable speed. In the event they cannot achieve a stable speed because they are never running at the same speed, aka cogging. @billwojo the evidence is in the engineering specifications of DD turntables that state they have constant speed monitoring and adjustment. Written in black and white.
As Dover says, this is analogous to digital control of digital sources where clock error is responsible for perceived speed instability known as jitter.
The alternative approach of using high platter mass and Newton's first law to maintain speed consistency through inertia is a far better approach.