Digital Optical Cables Explained: Everything You Need to Know

That glowing red light coming from your TV or soundbar? That's a digital optical connection at work. Also known as TOSLINK or S/PDIF optical, these cables have been quietly connecting audio equipment for decades. But in a world of HDMI and Bluetooth, do optical cables still matter? Absolutely—and understanding when to use them can significantly improve your audio setup.

Let's demystify digital optical cables and help you decide if they're right for your system.

What is a Digital Optical Cable?

A digital optical cable transmits audio as pulses of light through a fiber optic core. Unlike traditional copper cables that carry electrical signals, optical cables use light, which offers some unique advantages.

How It Works

1. Your source device (TV, game console, etc.) converts audio to a digital signal
2. A small LED or laser converts that signal to light pulses
3. The light travels through the fiber optic cable
4. The receiving device converts light back to a digital signal
5. A DAC (Digital-to-Analog Converter) turns it into sound

The Technical Specs

The red glow you see isn't just for show—it's actually the light carrying your audio signal. If you don't see the glow when connected, the cable or port may be faulty.

Optical vs. Other Audio Connections

Understanding how optical compares to alternatives helps you choose the right connection.

Optical vs. HDMI

When to choose optical over HDMI: - Your TV doesn't have ARC/eARC - You're experiencing HDMI handshake problems - You want guaranteed interference-free audio - Your soundbar only has optical input

Optical vs. Coaxial Digital

Both carry the same digital audio formats, but: - Optical: Immune to electrical interference, can't ground loop - Coaxial: Slightly better jitter performance, more durable connector

For most home setups, the difference is inaudible. Choose based on what ports you have available.

Optical vs. Analog (RCA)

Optical is generally superior for surround sound. Analog can be better for stereo if you have a high-quality external DAC.

What Optical Cables Can (and Can't) Do

Supported Audio Formats

Optical cables support: - PCM Stereo: Uncompressed 2-channel audio (CD quality) - Dolby Digital (AC-3): Compressed 5.1 surround - DTS: Compressed 5.1 surround

NOT Supported

Due to bandwidth limitations, optical cannot carry: - Dolby TrueHD: Lossless surround (Blu-ray) - DTS-HD Master Audio: Lossless surround (Blu-ray) - Dolby Atmos: Object-based surround (unless Dolby Digital Plus) - Uncompressed 5.1/7.1: Too much data

This is optical's main limitation. For the highest quality audio from Blu-rays or streaming services with Atmos, you need HDMI eARC.

Choosing the Right Optical Cable

Cable Quality: Does It Matter?

Here's the truth: for digital optical cables, expensive doesn't mean better. The signal is digital—it either arrives perfectly or it doesn't. There's no "better quality" digital signal.

What actually matters: - Build quality: Durable connectors that won't break - Proper length: Don't buy longer than needed - Fiber quality: Glass fiber is more durable than plastic for long runs

What doesn't matter: - Gold-plated connectors (light doesn't care) - "Audiophile grade" marketing - Prices over $20 for typical lengths

Recommended Cables

Budget Pick: AmazonBasics Optical Cable - Works perfectly for most setups - Durable enough for home use - Around $8 for 6 feet

Mid-Range: Monoprice Premium - Better build quality - Braided jacket for durability - Around $12 for 6 feet

Long Runs: FosPower Glass Fiber - Glass core for longer distances - Better bend radius tolerance - Around $15 for 10 feet

For more on audio connections, check out our guide on best Dolby Atmos soundbars.

Common Uses for Optical Cables

TV to Soundbar

The most common use case. If your TV has optical out and your soundbar has optical in, this is often the simplest, most reliable connection.

Setup:

1. Connect optical cable from TV's "Optical Out" to soundbar's "Optical In"
2. Set TV audio output to "Optical" or "External Speakers"
3. Set audio format to "PCM" or "Bitstream" depending on soundbar capabilities

Game Console to Audio System

Older consoles (PS4, Xbox One) have optical outputs. Newer consoles dropped optical but can output via TV.

For older consoles: - Connect directly from console to soundbar/receiver - Enables game audio without routing through TV

CD/DVD Player to Receiver

Classic use case for optical. Sends digital audio directly to your receiver for processing.

Computer to DAC

Many desktop DACs have optical inputs. Useful for: - Isolating computer audio from electrical noise - Using an external DAC for better sound quality

Troubleshooting Optical Connections

No Sound

1. Check the red light: Remove the cable and look for the glow. No light = source problem
2. Verify TV settings: Audio output must be set to optical
3. Check format: Try switching between PCM and Bitstream
4. Reseat connections: Remove and firmly reinsert both ends
5. Try another cable: Cables can fail, especially at the connectors

Sound Cuts Out Intermittently

- Loose connection: Optical connectors can work loose - Cable damage: Check for kinks or bends - Format mismatch: Source sending format receiver can't decode - Cable too long: Try a shorter cable

Lip Sync Issues

Audio arriving before or after video is common with optical: - Check TV settings: Many TVs have audio delay adjustment - Check soundbar settings: Look for lip sync or audio delay - Try different audio format: PCM sometimes syncs better than Bitstream

Only Getting Stereo (No Surround)

- Check source: Is it actually outputting surround? - Check TV settings: Some TVs downmix to stereo by default - Verify format: Set to Bitstream/Passthrough, not PCM - Check soundbar: Ensure it supports Dolby Digital/DTS

Optical Cable Care and Handling

Do's

- Store with protective caps on connectors - Use gentle curves, not sharp bends - Keep connectors clean and dust-free - Route away from foot traffic

Don'ts

- Don't bend sharply (minimum 30mm bend radius) - Don't step on or crush the cable - Don't leave connectors exposed to dust - Don't pull on the cable to disconnect

Cleaning Connectors

If you're getting signal issues:

1. Blow compressed air into the port
2. Use a lint-free cloth on the connector tip
3. Never use liquids or abrasives

When to Use Optical (and When Not To)

Use Optical When:

- Your TV lacks HDMI ARC/eARC - You're experiencing HDMI handshake issues - You want simple, reliable audio connection - Your equipment only has optical ports - You're connecting older devices

Don't Use Optical When:

- You want Dolby Atmos or lossless audio - You have HDMI eARC available and working - You need to carry video and audio together - You're setting up a high-end home theater

Got Questions About Digital Optical Cables? Let's Clear Things Up.

Are expensive optical cables worth it?

No. Digital signals either work or they don't—there's no quality gradient. A $10 cable carries the same signal as a $100 cable. Spend money on build quality if you need durability, but don't expect better sound from expensive cables.

Can optical cables carry Dolby Atmos?

Only in limited form. Optical can carry Dolby Digital Plus, which can include Atmos metadata for soundbars. However, it cannot carry full Dolby TrueHD with Atmos from Blu-rays. For the best Atmos experience, use HDMI eARC.

How long can an optical cable be?

Most plastic fiber cables work reliably up to 10 meters (33 feet). Glass fiber cables can go longer—up to 30 meters in some cases. For runs over 10 meters, choose glass fiber and test before permanent installation.

Why does my optical cable glow red?

That's the light carrying your audio signal! The LED or laser in the source device creates red light (around 650nm wavelength) that pulses to represent digital audio data. If you don't see the glow when connected, check that the source is powered on and outputting to optical.

Can I use optical and HDMI at the same time?

Usually yes, but only one will be active. Most devices let you choose which output to use. Some setups use HDMI for video and optical for audio, though this is less common now that HDMI ARC/eARC handles both.

Ready to optimize your audio setup? Explore more home theater guides at Celmin to get the best sound from your system. https://celmin.ca