# On-Off vs. Time Code (TCAP) synchronization signal

In order to synchronize external data and EthoVision XT tracking data, you can send out a synchronization signal with time information (SyncOut) from the EthoVision XT computer to the DAQ device. This signal is sampled by the DAQ computer and after acquisition imported into the EthoVision computer as a home coming signal where it is compared with the original synchronization signal.

On-Off and Time Code (TCAP: Time Code Auxiliary Parity) are two types of signals that reflect two ways of synchronizing external data (for example, heart rate) with tracking data.

On-Off

This signal is sent from EthoVision XT to the DAQ device shortly after a trial is started and stopped. Note that the On and Off signal are not sent at the exact moments of trial start and stop. The difference in offset between the synchronization signal and reference signal is calculated at the start and at the end of the recording. In order for synchronization to be successful, the DAQ recording must start before starting acquisition in EthoVision XT, and end after stopping acquisition in EthoVision XT.

A dialog in EthoVision XT informs you to start and stop data acquisition on your DAQ device. Furthermore, the DAQ recording should not be stopped during acquisition in EthoVision XT, which means that you cannot use the On-Off signal when performing scheduled sampling (that is, starting and stopping DAQ acquisition at regular intervals).

The relationship between Trial acquisition, the On-Off synchronization signal from EthoVision XT and acquisition on the external DAQ system.

Time Code

A series of bits called a frame is sent from the EthoVision XT computer to the external DAQ device. Each frame contains the current date and time and additional information. The difference in offset between the synchronization signal and the reference copy is calculated for several time points during acquisition (by default, for 10 time points), while the gain is calculated through regression analysis of offset values obtained at different points in time (that is, different frames). Therefore, synchronization of tracking and external data is more accurate using the Time Code signal because it is done for more than two offset points and not just at the start and stop of acquisition as with the On-Off signal.

The relationship between Trial acquisition, the Time Code synchronization signal from EthoVision XT and acquisition on the external DAQ system.