Sync Groups in DTRACK: time-shifted camera flashes — when they help and when to avoid them
DTRACK Sync Groups (Sync Channels) prevent mutual blinding between tracking cameras — how the 480 µs time shift works, use cases for multi-level setups, and when Static Reflex Suppression is the better choice.
What are Sync Groups — and why do you need them?
(This guide applies to DTRACK3 and DTRACK4 with ARTTRACK5, ARTTRACK6/M, and AT7-50/80 single cameras.)
In DTRACK, the camera menu lets you assign each tracking camera to one of three Sync Groups (also called Sync Channels). This controls when a camera sends its IR flash and when its sensor is active — not all cameras at the same time.
This matters especially with passive markers: each camera sends invisible infrared flashes that illuminate the tracking volume. Passive markers retroreflect that light back to the respective camera — see Retroreflection — how glass beads make our tracking possible for the physics behind it.
How do Sync Channels work technically?
Active time is the period when a camera sends the IR flash and the sensor is sensitive — typically 380 µs per frame. This is followed by a 100 µs gap, so one sync group slot lasts 480 µs in total.
The three Sync Channels are time-shifted by default:
| Channel | Start relative to sync signal |
|---|---|
| Channel 1 | with the sync signal (from DTRACK or an external source) |
| Channel 2 | 480 µs later (380 µs active + 100 µs gap after Channel 1) |
| Channel 3 | 960 µs after Channel 1 |
Delays can be adjusted under Hardware → SyncCard → Direct Settings — but that is only necessary in rare cases.
Avoiding mutual blinding
Depending on camera positions — usually adapted to the specific physical setup — cameras may see each other. If part of one sensor lies in the field of view of an opposing camera, that camera's IR flash can overexpose the other sensor (mutual blinding) when both are active at the same time.
Solution with Sync Groups: assign cameras that could interfere with each other to different channels. Camera 2 starts 480 µs after Camera 1 — and is no longer affected by Camera 1's flash. If a third camera sees both Camera 1 and Camera 2, assign it to Channel 3.
This is especially useful when:
- cameras are mounted at different height levels,
- for ergonomics and finger tracking applications,
- when setups require 360° movement of tracked objects.
Mutual blinding can also be handled with Static Reflex Suppression — but masked areas then no longer contribute to tracking. With Sync Groups, no masking is needed: the full sensor area remains available.
When Sync Groups are not recommended
For fast target movements (marker velocities well above everyday motion), different Sync Channels are counterproductive. The time delay between channels leads to skewed measurements or tracking dropouts — especially at velocities above roughly 4 m/s.
In those cases, mutual blinding should be addressed with Static Reflex Suppression, not different Sync Channels.
Many cameras in a small space: signal-to-noise ratio
In rare setups with many cameras in a relatively small volume — typically where multiple occlusions occur, e.g. in car interiors, seat bucks, or confined spaces — distributing cameras across all three Sync Channels can help.
More cameras increase redundancy against occlusions. But no matter how many cameras are in the system, the signal that matters for tracking — IR radiation retroreflected from the same camera's flash — stays the same per camera. However, when all cameras are active simultaneously (same Sync Channel), background radiation increases with each additional camera — the signal-to-noise ratio (SNR) gets worse. Then distributing cameras across all three Sync Channels can minimise SNR degradation.
Prerequisite: target velocities must not be too high (see above).
Practical assignment tips
- Opposing or adjacent cameras in each other's field of view → different Sync Channels (e.g. Channel 1 and 2).
- Cameras on the same wall, outside each other's field of view → same Sync Channel.
- Use the 2D Monitor: set flash intensity of all cameras to 0, then raise each to maximum one by one — this helps identify interfering cameras (see also Tracking quality dropping? Room calibration first).
- With modulated flash for active targets: affected cameras must be assigned to Sync Group #1 (DTRACK FAQ).
Next steps
- Calibration & targets: Target calibration in DTRACK — practical tips
- Room calibration: Tracking quality dropping? Room calibration first
- Software: DTRACK4 features and downloads
- Ergonomics & MoCap: Ergonomics solutions
- Plan your project: Tracking configurator or book a consultation