Optical Audio vs HDMI for Sound

Most TVs still offer two ways to send sound to a soundbar or amplifier: a small square optical port and an HDMI port marked ARC or eARC. The optical audio vs HDMI choice decides which formats arrive, whether one remote runs the system, and how much fault-finding the install needs. This guide explains what each connection is built to carry, how lip sync behaves, and when the older optical link is still the right answer.

What optical audio (TOSLINK) carries

Optical audio, often called TOSLINK after its connector, sends the S/PDIF digital audio signal as pulses of light down a fibre. The interface is defined by the IEC 60958 series. The IEC 60958-1 standard describes it as a serial, uni-directional, self-clocking interface, primarily intended to carry mono or stereo programmes encoded as linear PCM, with up to 24 bits per sample at sampling frequencies of 32 kHz and above.

The same document says the interface can also carry audio coded other than as linear PCM. That is how optical delivers compressed 5.1 surround: the TV or player sends an encoded bitstream, defined in the companion IEC 61937 series, and the soundbar or receiver decodes it.

• Can carry: two-channel PCM, or one compressed surround bitstream.
• Cannot carry: video, control commands, or a return path. It is one way, from source to audio device.

What HDMI adds over a digital audio cable

HDMI runs audio, video and control over one cable. Between a source and a receiver it carries the audio formats directly. From a TV back to a soundbar, the Audio Return Channel does the job: ARC carries roughly what optical carries, and eARC adds uncompressed and lossless multichannel audio. Our guide to HDMI ARC vs eARC covers the formats in detail.

The practical gain is control. HDMI CEC lets the TV remote set the soundbar’s volume and power both devices together. An optical link cannot do this, because nothing travels back from the audio device to the TV.

Optical audio vs HDMI compared

The table compares the two as connections, not just as audio formats. Format support is only part of the decision: direction, control and how the cable behaves on site matter as much on a real install, especially where the audio device sits away from the screen.

For a soundbar where the TV is the source switcher, HDMI wins on features. Where the job is a component system, compare the options in soundbar vs AV receiver first.

Lip sync over optical and HDMI

Lip sync error is sound arriving before or after the picture. TVs delay the picture while they process it, and soundbars delay audio while they decode it, so the two can drift apart on either connection. Because those delays depend on the processing in use, recheck sync after changing the picture mode or the audio format.

The window is small. EBU Recommendation R37, written for broadcasters, limits the end result to sound no more than 40 ms before the picture and no more than 60 ms after it. The figures come from subjective tests of when lip sync failure becomes perceptible to half of viewers.

A worked example puts that in context. Taking the speed of sound as about 1,125 feet per second, a listener 10 feet from the speaker hears it about 8.9 ms after it leaves. At 60 frames per second, each frame lasts 16.7 ms, so 60 ms is about 3.6 frames.

• On optical, the TV and soundbar cannot exchange timing information, so any correction is manual: an audio delay setting on the TV’s digital output or an AV sync setting on the bar.
• On HDMI, the two-way link lets devices that support it coordinate more, but still check for an audio delay setting when voices lag.

When optical is still the right answer

Optical is not obsolete. It is the better choice in several common cases:

• No ARC on one end: an older TV or an audio device without ARC leaves optical as the digital option.
• CEC conflicts: where CEC makes devices wake or switch inputs unpredictably, optical sidesteps it entirely.
• Feeding an amplifier: on commercial jobs, a TV’s optical output through a digital to analog converter can feed a mixer or zone amplifier, keeping the HDMI ports free for sources.
• Hum from a ground loop: because the link is light, the cable puts no electrical connection between the two devices, which can help when hum comes from the audio connection.
• Stereo music: for two-channel PCM, optical and ARC carry the same kind of signal.

For distributed systems built on a converter feed, our guide to whole house audio wiring covers the speaker side.

Cable length and handling

Consumer optical leads usually use plastic fibre and are rated by their makers for short runs between neighbouring devices. Check the rating of the specific lead, and plan a converter or move the equipment if the run is long. HDMI length depends on the signal and cable type; see HDMI cable length limits.

• Do not kink or crush an optical lead. A sharp bend can crack the fibre and stop the signal.
• Keep the dust caps on unused ports and cable ends, and push the plug in until it seats.
• If there is no sound, check the TV’s digital output setting first; a surround bitstream only works when the audio device can decode it.

Where to find HDMI and digital audio cables

The audio video cables category lists HDMI cables from short patch leads to 35, 50 and 60 foot active runs. Soundbars, receivers and mounts sit in the audio and video division.

For pricing and availability, ask your sales representative through the Bursma contact page, or open a Bursma dealer account.

Frequently asked questions