> For the complete documentation index, see [llms.txt](https://support.4cast.world/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.4cast.world/4.-timecode-setup/ltc-audio-timecode-setup.md).

# LTC (Audio Timecode) Setup

LTC (Linear Timecode) allows you to synchronize the MVP's video and lighting playback using a SMPTE timecode signal sent over an audio connection.

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## Hardware Connection

Connect your timecode source to the **3.5mm (1/8") audio input** on the rear of the MVP using a standard audio cable.

<figure><img src="/files/8ZArguIYlao3GOIsKjVa" alt="" width="563"><figcaption></figcaption></figure>

**Common LTC sources:**

* DAW audio output (dedicated timecode track)
* Click track with embedded LTC
* Dedicated LTC/SMPTE generator

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## Signal Verification

Before building your timeline, verify the MVP is receiving a clean LTC signal.

1. Start playback on your LTC source.
2. Navigate to the MVP **Dashboard**.
3. Check the **Input Monitor** section (LTC meters only appear when LTC signal is detected):

<figure><img src="/files/FXsV2FO8oLg4LJ3fQebR" alt="" width="473"><figcaption></figcaption></figure>

### What to Look For

| Indicator            | Healthy Signal                            | Problem                                              |
| -------------------- | ----------------------------------------- | ---------------------------------------------------- |
| **LTC Volume**       | Green bar, moderate level (-20dB to -1dB) | Orange = too quiet; Red = clipping; "--" = no signal |
| **Frames Decoded**   | Green bar, 100%                           | Orange/red = increasing frame loss                   |
| **Timecode Display** | Numbers running smoothly (HH:MM:SS:FF)    | Frozen or jumping = adjust volume                    |

### Adjusting Signal Level

If the timecode is frozen, erratic, or not appearing:

* **Too quiet**: Increase the output volume on your source device. Levels below -40dB are treated as no signal.
* **Too loud (clipping)**: Decrease the output volume. Levels above -1dB indicate clipping.
* **Just right**: The LTC Volume meter shows green with consistent moderate activity and the timecode counter runs smoothly.

The sweet spot varies by source, but aim for a signal in the -20dB to -1dB range.

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## Frame Rate Detection

The MVP detects the incoming LTC frame rate automatically.

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## Using LTC with the Timeline Editor

Once your signal is verified, you're ready to build your show in the [Timeline Editor](/4.-timecode-setup/the-timeline-editor.md):

1. Navigate to the **Timecode** page
2. Set the **Frame Rate** to match your LTC source (24, 25, 29.97, or 30 fps)
3. Place video and lighting clips on the timeline at the desired timecode positions
4. Start your LTC source -- the MVP will follow the timecode and play clips at the correct positions

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## LTC Signal States

The MVP's timecode engine tracks the LTC signal through four states:

| State                  | Dashboard Shows                       | What Happens                                   |
| ---------------------- | ------------------------------------- | ---------------------------------------------- |
| **No Signal**          | Inactive (gray)                       | Idle, waiting for timecode                     |
| **Active**             | Active (green), running SMPTE display | Video/lighting playback driven by timecode     |
| **Signal Interrupted** | Active, timecode continues            | Playback continues smoothly on internal timing |
| **Signal Lost**        | Inactive, playback stops              | Video goes to black, lighting holds last state |

When the signal returns after being lost, the MVP resumes sync.

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## Important Notes About LTC

* **Continuous sync**: The MVP uses LTC for **full continuous synchronization** -- the timecode position drives the playback position on the timeline at all times. This is not a one-time trigger.
* **Variable speed**: The MVP can follow LTC sources playing at 50% to 200% of normal speed. If your source runs slightly fast or slow, the MVP detects the rate and adjusts playback to match.
* **LTC and MTC are both active**: Both inputs are always listening. Whichever signal arrives drives playback -- there is no priority between them.

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## Related Pages

* [Timecode Overview](/4.-timecode-setup/timecode-overview.md) -- LTC vs. MTC comparison and capabilities
* [The Timeline Editor](/4.-timecode-setup/the-timeline-editor.md) -- Building your show timeline
* [MTC (MIDI Timecode) Setup](/4.-timecode-setup/mtc-midi-timecode-setup.md) -- Alternative MIDI-based timecode
* [All-Intra Video & Timecode Sync](/4.-timecode-setup/all-intra-videos.md) -- Frame-accurate seeking