More and more soundbars also support higher sound formats such as Dolby Atmos. Dolby Atmos can only be transmitted via HDMI and no longer via SPDIF audio connection. SPDIF (with Toslink or coaxial RCA connector) allows a maximum of Dolby Digital / DTS 5.1 in bitstream format. The bandwidth is not enough for more.
Of course, all soundbars with Dolby Atmos support have at least one HDMI connection. There are two ways the signal is transmitted:
HDMI or HDMI ARC / HDMI eARC
The audio-video signal is transmitted via HDMI 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 an AV receiver and can be connected between source and sink. The soundbar has 2 HDMI connections, one or more inputs and one HDMI output.
The HDMI Audio Return Channel (ARC) has been around for almost 10 years. Advantage: If the soundbar supports ARC, the audio signal path can also be used in reverse. The output of the soundbar is connected to the HDMI-ARC input of the television. Then the TV delivers the sound in reverse to the soundbar. The internal TV speakers turn off and you can hear audio from cable TV, apps and other HDMI sources through the sound system.
The soundbar is connected to the TV input with the HDMI output, and the sound comes in the opposite direction on the way back. You can understand this well if you switch to the HDMI input on the television to which the soundbar is connected. Then either the menu of the soundbar is displayed or simply a pattern.
HDMI-ARC Limitations and Opportunities
There are a few challenges when connecting via ARC:
- Some televisions only deliver stereo sound from external sources via HDMI-ARC and no surround sound. Whether this is a design flaw in the chipset or an economy measure is unclear.
- ARC was specified to carry the same formats as SPDIF. So maximum DTS and Dolby Digital 5.1. Technically, however, more is possible. Many TVs from LG since around 2016, including all Dolby Vision TVs, can output Dolby Digital Plus (DD+) 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 televisions from other manufacturers have also extended the ARC specification and deliver Dolby Atmos.
- HD audio formats such as Dolby True-HD and DTS HD Master Audio or uncompressed multi-channel sound PCM5.1 / PCM7.1 cannot be transmitted via ARC at all - only from the successor standard eARC in soundbars from 2020. These formats are usually found on Blu- Ray or computer games.
- There are streaming boxes like apple tv, that do not output audio as a bitstream. Instead, the multi-channel sound is already decoded in the box and transmitted on separate audio channels. Advantage: Operating sounds such as clicks and Siri can be used during movie playback. Disadvantage: multi-channel PCM cannot be transmitted via HDMI-ARC. This is only possible with completely new HDMI 2.1 televisions and eARC. The output on the Apple TV can be switched to "Dolby Surround", so that an ARC-compatible bitstream with Dolby Digital 5.1 is output. With many televisions there is a chance that this will be transmitted via HDMI-ARC. But this is not possible for DD+ / Dolby Atmos. The same applies to an Xbox.
- Google Chromecast on the other hand, it delivers either stereo or DD+. This streaming adapter does not know "normal" Dolby Digital 5.1 in most apps. TVs without DD+ support only output stereo to the soundbar.
- More on the subject: ARC and HDMI CEC (used for volume control, among other things)
If you want to use the highest sound quality from Apple TV, Xbox, PC, Nintendo Switch or Chromecast, you can only do this on a sound system with a "real" HDMI input or via HDMI-eARC. If the soundbar only has a single HDMI connection, this is always an HDMI output that supports ARC or eARC.
Soundbars with ARC or eARC and only a single HDMI port depend on the capabilities of the TV. These include Sonos Arc, Sonos Beam and Bose Soundbar 500, 700, 900. Such soundbars cannot be operated on an HDMI splitter because there is no "real" HDMI input. Connecting to a video projector is also difficult.
We have therefore developed special HDMI switches to which such soundbars can be connected via HDMI. The VAX04100 model is used to connect 3 HDMI sources to an HDMI-ARC soundbar and TV or projector. It supports sound formats up to DD+ / Dolby Atmos via HDMI-ARC. The VAX04101 version communicates via HDMI-eARC and can also transport DolbyTrue HD (e.g. from Blu-Rays) and Dolby MAT (e.g. from Apple TV). The Sonos Soundbars Arc and Beam Generation 2 (with eARC) only work on the VAX04101.