Sound bars and HDMI ARC

More and more soundbars are supporting higher-resolution audio formats like Dolby Atmos. Dolby Atmos can only be transmitted via HDMI and no longer via SPDIF audio connection. SPDIF (with Toslink or coaxial RCA connectors) only allows a maximum of Dolby Digital/DTS 5.1 in bitstream format. The bandwidth is insufficient for anything more.

Naturally, all soundbars with Dolby Atmos support have at least one HDMI port. There are two ways the signal is transmitted:

HDMI or HDMI-ARC / HDMI-eARC

HDMI transmits the audio-video signal from a source (streaming box, PC, game console, TV receiver) to the HDMI sink (television, projector, AV receiver). The HDMI source has an HDMI output, and the sink has an HDMI input. Most soundbars are equipped like AV receivers and can be connected between the source and sink. For this purpose, the soundbar has two HDMI ports: one or more inputs and one HDMI output.

The HDMI Audio Return Channel (ARC) has been around for almost 10 years. The advantage: If the soundbar supports ARC, the audio signal can also be used in reverse. The soundbar's output is connected to the TV's HDMI ARC input. The TV then sends the audio signal back to the soundbar. The TV's internal speakers are muted, and you hear the audio from cable TV, apps, and other HDMI sources through the sound system.

The soundbar is connected to the TV's HDMI input via its output, and the sound travels back in the opposite direction. You can easily verify this by switching to the HDMI input on the TV to which the soundbar is connected. Either the soundbar's menu will be displayed, or a pattern will simply appear.

HDMI-ARC limitations and possibilities

There are a few challenges when connecting via ARC:

1. Some TVs only output stereo sound from external sources via HDMI-ARC and not surround sound. It's unclear whether this is a design flaw in the chipset or a cost-cutting measure.
2. ARC was specified to transmit the same formats as SPDIF. So, at most, DTS and Dolby Digital 5.1. Technically, however, more is possible. Many televisions from LG Since around 2016, including all Dolby Vision TVs, Dolby Digital Plus (DD+) can output via ARC. Services like Netflix, Amazon Prime, Sky, and Disney+ use DD+ to transmit Dolby Atmos. Many Samsung TVs have also been able to output DD+ since 2019. Some TVs from other manufacturers have also extended the ARC specification to deliver Dolby Atmos.
3. HD audio formats such as Dolby TrueHD and DTS HD Master Audio, or uncompressed multi-channel sound PCM5.1 / PCM7.1, cannot be transmitted via ARC at all – only by the successor standard eARC in soundbars from 2020 onwards. These formats are typically found on Blu-ray discs or computer games.
4. There are streaming boxes like Apple TV, The audio is not output as a bitstream. Instead, the multi-channel sound is decoded within the device and transmitted on separate audio channels. Advantage: Control sounds like clicks and Siri can be used during movie playback. Disadvantage: Multi-channel PCM cannot be transmitted via HDMI-ARC. This is only possible with very new HDMI 2.1 TVs and eARC. The output on Apple TV can be switched to "Dolby Surround," so that an ARC-compatible bitstream with Dolby Digital 5.1 is output. Many TVs have a chance of transmitting this via HDMI-ARC. However, this is not possible for DD+ / Dolby Atmos. The same applies to an Xbox.
5. Google Chromecast and Fire TV Lite, on the other hand, deliver either stereo or Dolby Digital 5.1. These streaming adapters don't support "normal" Dolby Digital 5.1 in most apps. Therefore, TVs without Dolby Digital 5.1 support will only output stereo to the soundbar.
6. More on this topic: ARC and HDMI-CEC (used, among other things, for volume control)

To enjoy the highest sound quality from Apple TV, Xbox, PS5, PC, Nintendo Switch, or Chromecast, you need a sound system with a "real" HDMI input or via HDMI eARC. If the soundbar only has a single HDMI port, it will always be an HDMI output that supports ARC or eARC.

Conclusion:

Soundbars with ARC or eARC and only a single HDMI port are dependent on the capabilities of the television. This includes the Sonos Arc, Sonos Beam, and Bose Soundbar 500, 700, and 900. Such soundbars cannot be used with an HDMI splitter because they lack a "real" HDMI input. Connecting them to a video projector is also more difficult.

We have therefore developed special HDMI switches to which such soundbars can be connected via HDMI. The AX310 model is used to connect one HDMI source, the AX340 for up to four HDMI sources to an HDMI eARC soundbar and a display. The AX341 version is designed for two screens (e.g., a TV and a projector).