Fixing LG OLED CX Sound Out of Sync During Movies

Introduction

A crisp picture and a crystal‑clear soundtrack are what turn a regular movie night into an unforgettable experience. On the LG OLED CX, however, many viewers have reported that the audio falls out of sync with the video, especially during high‑action scenes. The delay can be subtle at first and then grow more noticeable as the film progresses. While the problem may feel frustrating, it is almost always solvable with a methodical approach. This guide walks you through a series of troubleshooting steps and settings adjustments that can restore perfect sync between sound and picture.

Understanding Audio‑Video Sync

Audio‑video (AV) sync is the alignment of sound and image in real time. Even a half‑second lag can break immersion, making a punch sound too early or a dialogue line too late. The brain perceives a mismatch as jitter or ghosting, which is why many people are sensitive to it. On modern TVs, AV sync is usually handled by the processor, but external devices such as soundbars, AV receivers, or streaming players can introduce their own delays.

When the LG OLED CX displays a sync problem, you are seeing the combined effect of several potential sources:

1. Internal TV processing – the GPU, video decoding, or audio output path.
2. HDMI/ARC/eARC latency – the cable and the interface can add delay.
3. External audio device processing – soundbars, receivers, and subwoofers can buffer audio.
4. Source content encoding – some movies embed audio delay information that the TV may misinterpret.

The next sections will cover each of these areas and provide practical solutions.

Common Causes of Sync Issues on the LG OLED CX

Understanding these causes helps you focus on the right settings before you spend time tweaking every option.

Quick Fixes: Reset and Restart

Before diving into complex settings, start with the basics. Many sync issues are resolved simply by rebooting the system or performing a soft reset.

1. Turn Off All Devices – Power down the TV, the receiver or soundbar, and the source (Blu‑ray player, streaming stick, console).
2. Unplug for 30 Seconds – Disconnect the TV from power and let it sit for half a minute. This clears the internal cache.
3. Reconnect and Power On – Plug the TV back in and turn on each device in the following order: TV, then audio system, then source. This ensures a clean handshake.
4. Test a Short Clip – Play a short, well‑known clip to see if the lag persists.

If the lag disappears, the problem was likely a temporary glitch. If not, move on to the next steps.

Checking and Adjusting the TV’s Audio Delay Settings

The LG OLED CX has a built‑in Audio Delay slider that allows you to shift the audio timeline to match the video. The slider accepts values from –200 ms to +200 ms.

How to Access the Audio Delay Slider

1. Press the Settings button on the remote.
2. Navigate to All Settings → Sound → Expert Settings.
3. Scroll down to Audio Delay.
4. Use the arrow keys to increase or decrease the delay in 10 ms increments.

Tip
Start by setting the delay to 0 ms. Play a test video. If the sound still lags, try positive increments (+10, +20, +30 ms) until the audio lines up. If the sound jumps ahead of the picture, adjust in the negative direction (–10, –20 ms).

When to Use Audio Delay

• ARC or eARC Connection: ARC typically adds delay, so positive values help. eARC usually keeps delay minimal, but if your receiver still lags, try a small negative value.
• External DACs: If you use a separate DAC or external processor, the audio may arrive slightly earlier. Use a negative delay to compensate.
• Source Variation: Some Blu‑ray discs or streaming services encode a specific audio delay. In those cases, the TV’s delay slider may need to be tuned to match each source.

Using the LG Content Store for Firmware Updates

Firmware updates often contain performance improvements and bug fixes that directly affect AV sync.

1. Open the LG Content Store from the home screen.
2. Search for Updates or Firmware Update.
3. If an update is available, follow the on‑screen instructions to download and install.
   For a detailed step‑by‑step guide, see our post on how to keep the LG OLED CX’s picture quality after a firmware upgrade:
   How to Stop LG OLED CX from Losing Picture Quality After Firmware Upgrade
4. After installation, reboot the TV and test again.

If you are unable to connect to the internet, you can also use a USB stick with the latest firmware file downloaded from LG’s support website. Plug the USB into the TV, navigate to Settings → Support → Software Update → USB Update, and follow the prompts.

Configuring HDMI ARC/eARC

HDMI ARC is a convenient way to transmit audio back to a receiver or soundbar, but it can add a few milliseconds of delay. The newer eARC standard mitigates this but only if both the TV and the receiver support it.

Verify eARC Support

1. Check TV: In Settings → All Settings → General → About This TV, confirm that the HDMI port is labeled “eARC.”
2. Check Receiver: Look at the device manual or the labeling on the HDMI input. It should read “eARC” or “HDMI 2.1.”

If one device only supports ARC, switch to the regular ARC port.

Adjust ARC Settings

1. Go to Settings → All Settings → Sound → Audio Out → HDMI ARC.
2. Set ARC to Enabled and eARC to Enabled if available.
3. Enable HDMI‑CEC (also known as Simplink) to allow the TV to control the receiver’s power state.
4. Under Sound → Sound Out → Receiver or Soundbar, select Bitstream or PCM depending on what your receiver accepts best.

Choosing PCM can reduce delay on older receivers but may limit channel support. Bitstream maintains surround sound but might introduce a tiny buffer delay.

If you run into HDMI insertion errors, the Panasonic TV HDMI insertion error guide offers troubleshooting steps:
Resolving Panasonic TV‑75HZ2000 HDMI Insertion Error That Stops Video

Configuring Audio Output: Digital Audio Out vs PCM

When the TV sends audio to a receiver or soundbar, it can choose between two main formats:

How to Change the Format

1. Open Settings → All Settings → Sound → Sound Out.
2. Choose the audio device (e.g., “Receiver” or “Soundbar”).
3. Under Audio Format, toggle between PCM and Bitstream.
4. After changing, test a scene with sound effects to see if sync improves.

If switching to PCM eliminates the lag, you can keep it. If you need surround sound, try Bitstream with a small audio delay adjustment as described earlier.

Adjusting External Audio System Settings (AV Receiver or Soundbar)

Many AV receivers and soundbars have their own audio delay controls. It’s essential to set them to zero or a minimal value so the TV’s Audio Delay slider can work effectively.

Example Fixes

• Receiver Delay: Set the receiver delay to 0 ms and enable Auto Sync on the receiver if available.
• Soundbar Delay: Set the soundbar delay to 0 ms and adjust the TV delay to a small positive value (e.g., +15 ms).

For users of older receivers that might struggle with eARC, the professional technicians’ advice on hardware issues remains relevant:
When to Seek Professional Help

Advanced: Using a Delay Timer on the TV or External Audio Device

If all else fails, you can add a small, custom delay at either the TV or the external device. This is only recommended if you have ruled out other options.

Adding Delay on the TV

1. In Settings → All Settings → Sound → Expert Settings → Audio Delay, set a positive value (e.g., +50 ms).
2. Verify that the audio aligns.

Adding Delay on an External Device

Some receivers allow a custom delay setting in the “Audio Processing” menu. Set a positive delay (e.g., +30 ms) and test. Use this only if the TV delay setting is already at 0 ms and the lag persists.

If you encounter a situation where the TV shuts down during HDR playback, the Samsung Q90T shutdown guide provides an example of how to handle similar hardware‑level delays:
Eliminating Samsung Q90T from Shutting Down During HDR Playback

Troubleshooting Specific Scenarios

These targeted fixes often resolve the issue faster than sweeping changes.

When to Seek Professional Help

If you have tried every setting, updated firmware, and verified cable quality, yet the sync remains off, consider:

• Cable Quality: Replace the HDMI cable with a high‑speed 2.0 or 2.1 cable. Low‑grade cables can introduce unpredictable delays.
• Hardware Issues: The TV’s internal audio processor may be defective. A service call is warranted.
• Receiver Compatibility: Some older receivers cannot handle eARC properly. Consult the manufacturer’s support.

Professional technicians can run diagnostic tools that measure audio latency in milliseconds and identify hidden hardware problems.

Summary

Fixing a sound‑out‑of‑sync problem on the LG OLED CX is a systematic process:

1. Reset all devices and reboot.
2. Update firmware on TV and external hardware.
3. Check HDMI ARC/eARC connections and set the correct mode.
4. Select the proper audio format (PCM or Bitstream) on the TV.
5. Adjust the TV’s Audio Delay slider until sync is perfect.
6. Verify that external devices (AV receiver, soundbar) have zero or minimal delay settings.
7. Fine‑tune the settings for specific sources like Blu‑ray, streaming apps, and gaming consoles.
8. Use the TV’s Audio Sync feature for automatic adjustment when available.
9. Consider adding a custom delay only after all other options have been exhausted.
10. Contact professional support if the issue persists.

By following these steps patiently and methodically, you should be able to eliminate the audio lag and fully enjoy the immersive experience that the LG OLED CX is designed to deliver. Happy viewing!