What are the CLOCK IN specifications?

The terminal is a stereo mini-jack and inputs START/STOP and CLOCK signals.
The standard input voltage levels of each signal are 5V.
You can select CLOCK signals input from 7 output formats: 1step, 1ppqn, 2ppqn, 4ppqn, 24ppqn, 48ppqn, and GATE.
And, you can select CLOCK Polarity from Negative trigger ( − ) or Positive trigger ( +)
1step (1 Pulse Per Step): A pattern is advanced by one step when 1 pulse is input to the timing clock.
GATE: A pattern plays while the Gate signal is being input and pauses while no Gate signal is being input.

You can change these settings in the [CLOCK] setting category of the GLOBAL menu.
For details, please refer to "[CLOCK] setting" in "GLOBAL settings" in the Operating Instructions.
You can download the Operating Instructions from the AlphaTheta support page https://www.pioneerdj.com/en/support/documents/production/toraiz-squid/.