LTC Audio Output
LTC (Linear Timecode) is SMPTE timecode encoded as an audio signal — it sounds like a distinctive digital chirp on an audio cable. LTCast puts it on an audio output device so that any device with an LTC input (lighting console, media server, audio recorder, or another instance of LTCast) can lock to it.
Where the LTC comes from
LTCast has two sources, and only one is used at a time:
- The file's own LTC (normal playback) — when the loaded audio file carries an LTC channel, LTCast plays that channel straight to the LTC output device while the song plays. It is the signal that is in the file, passed through at the level you set. This does not need Pro.
- TC Generator — for a song that has no LTC, switch the main screen to TC Generator and LTCast encodes LTC from the playhead position and the song's Start TC. See TC Generator & start TC. Generating LTC is a Pro feature (a Pro licence or an active trial).
Recommended virtual audio setup
If you are routing LTC to software on the same computer rather than a physical cable, use a virtual audio device:
- Windows — install VB-CABLE (free, vb-audio.com). Select CABLE Input as the LTC output device in LTCast. Connect CABLE Output in the target application as its audio input.
- macOS — install BlackHole (free, ExistentialAudio GitHub). Select BlackHole as the LTC output device. Route BlackHole to your interface using Audio MIDI Setup → multi-output device if you also need to hear the music.
For physical cabling, select your audio interface output in the device selector and connect the interface's output channel to the LTC destination with a standard audio cable (balanced XLR or TRS recommended).
Configuring LTC output
Open Settings → Devices. Three controls there concern LTC output:
- LTC Output — the device that carries the LTC. The first entry in the list is Muted (decode only, no audio out), and it is the default: until you pick a real device, LTCast still reads the file's LTC for its own display, chase and triggers, but sends no LTC audio anywhere.
- CH 1, CH 2, … — the channel pills beside the device. LTC is a mono signal, so tick the channel your cable is connected to. Tick several to send the same LTC on all of them at once; untick every channel to mute LTC. Channels beyond the device's channel count are greyed out.
- LTC Track — which channel of the loaded audio file carries its LTC: Auto-detect (CH 1/2), or CH 1 to CH 4. Use it when auto-detect picks the wrong channel.
LTC Level is in Settings → Outputs. The slider runs from silence up to +3.5 dB, and 0 dB leaves the signal unchanged. The in-app hint recommends −3 to 0 dB for Resolume Arena; a device with an analog input may need a lower level so it does not clip its input stage. Right-click or double-click the slider to reset it to 0 dB.
When LTC is sent
LTC leaves LTCast only while a song is playing. When you pause or stop, and in the gap between two songs when Auto-advance is on, the LTC output is silent — LTCast does not repeat the last frame. A receiver that needs timecode all the time will report signal loss in those moments.
The Esc fade-out fades the music only. During the fade the LTC keeps playing at full level, so a receiver stays locked to the end of the fade. When the fade finishes the song stops and the LTC goes silent, like any other stop.
Verifying LTC output
Two things in the bottom status bar show the LTC state. The LTC pill lights while LTCast has timecode running — decoded from the file's LTC channel, or generated. The small level meter beside it shows what actually leaves the LTC device after the level setting; it stays empty while LTC is muted, paused or stopped. There is no "TX" label.
On the receiving device, confirm it shows timecode locked. If it shows no signal, check: the right LTC Output device and channel are ticked, the virtual audio device (VB-CABLE or BlackHole) is running, LTC Level is not at the bottom of the slider, and the song is actually playing.