SMPTE/MTC timecode for lighting: a practical introduction

Clock versus analysis

Live audio analysis follows whatever is in the feed. Timecode plays a known timeline. Use SMPTE or MIDI timecode when video, playback and lights must scrub together in rehearsal and hit the same frame on the night.

If the night is a DJ reading the room, timecode is the wrong master. If the night is a playback show with content on a timeline, timecode is the right master. Many events use both: reactive washes for the party, a timecode chunk for the one video drop that must land.

SMPTE, MTC and friends

Linear timecode (LTC / SMPTE) is an audio-like signal you can put on a track or a dedicated output. Machines read hours:minutes:seconds:frames. Frame rate must match the project: 24, 25, 29.97, 30, and drop-frame versus non-drop are not interchangeable.

MIDI timecode (MTC) carries the same idea over MIDI. Useful when the lighting computer already has a MIDI interface and the playback machine can emit MTC. Art-Net and other show protocols can also carry timecode — the clock is the point, the pipe is negotiable.

Internal clocks and cue lists can run without an external tape machine. That is fine for a sequence that starts when you press go. It is not the same as locking to a video server that might pause, scrub, or jump.

Frame rates and drop-frame

Pick the rate the video department already uses. Do not invent a lighting-only rate. 25 fps is common on PAL stages. 29.97 drop-frame exists because NTSC colour television was a compromise; if you do not know why you need it, you probably want 30 or 25 instead.

A one-frame offset is visible when a hit is tight. A one-second offset is a different show. Confirm the start-of-timeline together: some people call first frame 01:00:00:00, others 00:00:00:00.

How to run a locked cue

Build the cue list against the timeline in rehearsal. Chase the code. When the machine jumps, the lights should jump. If they drift, you have the wrong rate, a bad read, or a software chase that is following wall-clock instead of incoming code.

Always have a manual go and a blackout. Timecode readers fail. Files get replaced. The opener’s USB stick will be a different edit.

When not to use it

Do not lock a whole club night to a fake timeline “so it feels professional.” The room will leave the timeline. Use DSP and a human override for that job. Save timecode for moments that actually have a clock.

A rehearsal that actually tests lock

Scrub backwards. Pause. Jump to the chorus. If the lights smear or keep walking, you are chasing wall-clock or a free-running sequence. Fix the chase source before you add more cues.

Replace the file with a one-second-later edit and watch who notices first: video or lights. Align the zero. Then lock the rate in writing on the call sheet: “25 fps non-drop, hour 1 start.”

Keep a handheld go for the moment the reader dies. A silent timeline with no manual escape is not a professional show. It is a single point of failure with better branding.

Audio cables that carry time

LTC on a spare audio track will pick up hum and bleed if you treat it like a DJ send. Use a dedicated output, keep levels in the range the reader expects, and do not put it through a club EQ “because it is audio.” It is a clock that happens to look like audio.

If two machines disagree by a constant offset, you have a start-of-timeline argument, not a rate argument. If they drift, you have a rate or a bad read. Those are different fixes. Do not “nudge cues” for a drift problem; you will chase it all night.

MTC specifics

MTC is quarter-frame messages. A reader that only sees full frames may feel coarse when you scrub. That is normal. Do not “fix” it by switching to wall-clock. Confirm the sender is actually emitting MTC and not only a MIDI clock pulse.

If the lighting computer is also a DAW host, isolate ports. Lighting MTC on the same port as a synth bank is how transport buttons steal your blackout. Label the MIDI port “timecode only” and refuse other traffic on it.

Related

• Audio-reactive DSP →
• Recording & Timecode →
• Timecode calculator →