With On/Bypass you switch the module on or off (bypass).
The Sig LED (Sig) indicates whether an audio signal is present at the input and exceeds a level of -20 dB. This LED indicator is used as an aid to quickly identify whether a signal is arriving at the TDx in a complex studio cabling system.
Attack can be used to boost or cut the transient phase of a signal by up to 15 dB. Positive attack increases the amplitude of the transient response. Negative attack attenuates the amplitude of the transient response.
With Sustain you can lengthen or shorten the decay phase of a signal by up to 24 dB. Positive Sustain extends the decay. Negative Sustain shortens the decay.
The mix control allows for continuous crossfade aka parallel mix between processed (WET) and unprocessed (DRY) signals.
With the output control the output gain can be attenuated in order to optimally drive subsequent devices.