What is the difference between Analog and Digital volume controls?

Digitally Controlled analog circuits use an encoder to send digital information to an IC audio chip that accepts digital input.

The analog volume control in the Slate Control is a relay-controlled resistor ladder. This is known to be the best sounding and most accurate form of volume control. Control voltage from the volume knob is sent to the rack unit and the relays switch precision resistors in and out of the circuit to create volume steps in 1db increments.