mixing

A wet/dry setting is used to balance the processed (wet) signal with the unprocessed (dry) signal. This is a common setting on reverb plugins to control how much of the affected signal you want mixed in with the original.

Digital distortion is what happens when a signal goes above 0dBFS. Audio cannot be represented above this point and will distort. Digital distortion is particularly harsh sounding.

Automation is a system that memorizes and then plays back the position of faders, plugin controls, etc. Automation can be drawn/programmed in, or else inputted in realtime using a mouse or midi controller.

A fader automation lane in Ardour, controlling the level of the fader

A pre-delay setting is found on some reverbs. This setting allows you to set the length of time (in milliseconds) before the onset of the reverb, after the dry signal. This mimics how direct sound and sound reflections in a room arrive at our ears at different times. A short pre-delay will sound as if it is at the room boundaries, whereas a longer pre-delay will be perceived as being closer.

A MIDI controller is any device that sends out MIDI data to control another MIDI device or program. Some MIDI controllers are also capable of recieving MIDI data. Two examples of a MIDI controller would be a MIDI keyboard which can be used to control softsynths/external hardware synths or a MIDI DAW controller used to control fader/pan levels in your DAW as well as other things such as plugin parameters.

Not a setting on every compressor but some compressors have this option. This is related to how the threshold takes affect. A soft knee will introduce the compression more gradually, whereas a hard knee setting will be more abrupt. Both have their place but soft knee compression is considered to have a more pleasing effect.