LTC dropout checker
A dropout is a section of an LTC file where the timecode signal can't be decoded, or where it jumps or repeats unexpectedly. LTC Check scans the whole file and reports exactly where they happen.
What causes LTC dropouts?
LTC is an audio signal, so it inherits the failure modes of audio. Common causes include:
- Low signal level - LTC recorded too quietly can fall below what a decoder can reliably read.
- Clipping / distortion - LTC recorded too hot, or run through a stage that clips it, can distort the waveform enough to break decoding.
- Bad routing - the wrong channel, a muted send, or a cable/patch issue can produce silence or the wrong signal where LTC is expected.
- Edits in the timecode WAV - a cut, crossfade or edit made in an audio editor can break timecode continuity even if the surrounding audio sounds fine.
- Resampling or time-stretching - sample-rate conversion or time-stretching a file after LTC was recorded can distort or shift the timecode.
- Accidental gaps - silence inserted or a section deleted during editing or bouncing.
- DAW or rendering problems - bounce/export settings, sample-rate mismatches or plugin latency compensation can all introduce discontinuities.
Why LTC continuity matters
Downstream systems - playback software, lighting consoles, video servers - read LTC continuously and use it to stay in sync. A jump, dropout or repeated frame can affect how those systems behave, depending on how each one is implemented and configured: some interpolate through a brief dropout, others may jump, stall or lose sync. Because the behaviour varies by system, the safer approach is to check the timecode file itself before the show, rather than finding out during it.
How to test an LTC WAV file
A thorough check of an LTC file covers:
- Frame rate - is it what the show expects (24fps, 25fps, 29.97fps, 30fps)?
- Start time - does the file start where it should?
- Continuity - does every frame follow the last, with no gaps?
- Skipped frames - are any frame numbers missing?
- Repeated frames - is any frame duplicated where it shouldn't be?
- Backward jumps - does the timecode ever move backwards or restart?
- Decode dropouts - are there sections that don't decode at all?
- Signal integrity - is the LTC channel clean, at a sensible level, and free of clipping?
Doing this by ear or by spot-checking a waveform is slow and unreliable - a dropout lasting a fraction of a second is easy to miss. LTC Check automates this: it decodes the entire file and reports every dropout, jump and skipped or duplicate frame it finds, with its position in the file, so you can find detectable continuity and signal problems before you use the file in a show.
Related reading
- LTC timecode checker - what an LTC checker does in general.
- How LTC Check works - the full list of checks performed.