LTC Timecode Erratic / Jumping — Noise from Shared Power Supply¶
Summary¶
LTC SMPTE timecode displayed in Flair jumps erratically and does not hold a stable value, making TC-triggered moves unreliable. The cause is electrical noise on the LTC signal path, originating from a shared or mismatched power supply between the LTC source device and the robot system. The fix is to ensure all equipment (monitors, TC source, speakers, laptops, client monitors) is on the same power supply as the robot, or to use a battery-powered TC source.
Symptoms¶
- Timecode numbers jump erratically in the Flair TC display (not advancing steadily frame-by-frame)
- TC-triggered moves fire at the wrong time or not at all
- Bloop light glows faintly and constantly (even when no trigger is programmed) — indicates noise on the trigger line
- 10G Ethernet connection drops or becomes unstable (possible concurrent symptom from same power environment)
- Problem worsens when lighting rigs are active on set
Root Cause¶
The LTC signal enters the RT14 via a 3.5mm jack. The RT14's LTC input is not robustly isolated — it is susceptible to ground noise on the signal cable.
When the LTC source device (laptop, playback unit, TC generator, speaker) is powered from a different electrical source than the robot:
- A ground potential difference exists between the two systems
- This difference rides on the LTC cable as common-mode noise
- The RT14 interprets this noise as spurious timecode transitions, causing erratic TC readings
Tom David's confirmed root cause (2024): a speaker powered from a different GPO (general power outlet) was connected via XLR to the same audio chain as the LTC source. The different GPO created a ground differential, which was conducted down the XLR cable into the LTC signal path.
Additional contributing factors (from Mike Greenberg, 2023-12)¶
- Generator-powered location sets where different devices are on different phases
- BNC cables connecting devices on different power sources (e.g., monitors from generator, robot from separate supply)
- Client monitors and AV equipment on production power vs robot on dedicated supply
Fix¶
Option 1 — All Equipment on the Same Power Source (Recommended)¶
Ensure that every piece of equipment connected (directly or indirectly) to the robot system shares the same power supply:
- LTC source (laptop, generator, TC box)
- All monitors connected to the system
- Speakers / audio playback devices
- Client monitors and AV distribution equipment
- The robot control computer
Even indirect connections matter. If a speaker is connected via XLR audio to a device that is connected to the robot, and that speaker is on a different power outlet, noise can travel down the audio chain into the LTC input.
Indirect connections count
A speaker on a different GPO, connected via XLR to a mixer, connected via audio to a playback laptop, connected via USB to the robot PC — that chain can conduct ground noise into the LTC signal. Every device in the chain must share the robot's power source.
Option 2 — Battery-Powered TC Source (Cleanest Fix)¶
Use a battery-powered LTC generator or playback device. A battery-powered source is electrically floating — it has no mains ground reference and cannot create a ground differential with the robot system.
This completely eliminates power-related LTC noise regardless of the mains wiring environment on set.
Best practice for location work
On location sets with generators, multiple power sources, and mixed equipment, a battery-powered TC source is the most reliable solution. It removes the power environment from the LTC signal chain entirely.
Option 3 — Audio Isolation Transformer¶
An inline audio isolation transformer (DI box in reverse, or a proper audio isolator) on the LTC cable will break the ground connection while passing the audio-rate LTC signal. This is a valid fix if re-wiring power is impractical.
Bloop Light Glow Diagnosis¶
If the bloop light is glowing faintly and constantly (not just firing on trigger events), this is a strong indicator of noise on the trigger output line. It often shares a root cause with LTC noise — a ground differential or mains noise being conducted through the system. The same power-consolidation fix resolves both symptoms.
References¶
- Tom D — diagnosed December 2023, confirmed March 2024
- Mike Greenberg — multiple location incidents, December 2023
- SYNC-ltc-timecode-setup — LTC setup and wiring
Official Documentation¶
WhatsApp Excerpts¶
- 2023-12-01 12:27 - Tom D: Hello, today we are having lots of trouble getting a stable LTC signal into the rt box with our bolt in track. We’ve tried several tried and tested timecode sources however having no luck getting a stable reading in flair. Numbers jumping around very erratically and not vaguely close to actual LTC numbers. We’ve tried our usual tricks of varying volume etc (playing audio LTC off a timeline) but suspect we’ve some weird noise in the system. For example, the bloop light is very vaguely flashing...
- 2023-12-01 12:28 - ~ Mike Greenberg: Check that the timecode source is on separate power than the bolt. Even better to check by using a battery powered option (speaker/laptop) We had interference like this from dirty power once.
- 2023-12-01 12:29 - Tom D: Thanks Mike - it’s on the same power source as the bolt, yes.
- 2023-12-01 12:30 - Tom D: We can hear the timecode playing on a speaker if we switch channels - so suspect there’s some interference going on in the rt box
- 2023-12-01 16:25 - ~ Heiko Matting: Latest bug I found due to this is a boom box with Akku running on DC power connected to the second mono channel of the LTC source. As soon as the power cable was stripped off, it was working well.