Ask S&V

A What’s the problem with HDMI Audio Return Channel (ARC)? I’ve heard that most people simply give up on ARC and use an optical digital audio connection from their TV to their receiver instead because they can rarely get it to work between devices, especially ones from different manufacturers. What can the HDMI Forum do to improve the situation? —Phis Tomaskovic / via e-mail

Q The HDMI Forum already has taken steps to improve the situation by drafting the HDMI 2.1 specification. The new HDMI spec incorporates a long list of advancements to ensure compatibility with future technologies such as 8K/60fps and 4K/120fps video, but also addresses several limitations in the existing HDMI 2.0a spec, including ones surrounding ARC.

A key feature that HDMI 2.1 will bring is Enhanced Audio Return Channel (eARC). With eARC, audio signals benefit from higher bandwidth to support everything from Dolby Digital Plus and lossless Dolby True HD/DTS-HD Master Audio bitstreams to object-based formats like Dolby Atmos and DTS:X. This development is particularly important as more of us start to stream movies with multichannel and object-based audio soundtracks through our TVs, as opposed to playing them on physical discs.

Another aspect of eARC is advanced device control. ARC, which was first introduced in the HDMI 1.4 spec, relies on the HDMI CEC (Consumer Electronics Control) protocol. A problem with CEC is that different manufacturers use their own unique implementations (Bravia Link, Viera Link, etc.). CEC is also an optional feature that’s not required for certification of products by the HDMI Forum. HDMI 2.1, in contrast, will include a robust auto-detect mechanism plus more advanced audio signal control capabilities than what the current CEC specification provides.

HDMI 2.1 will require a new cable to support its full range of features. However, according to an HDMI Forum FAQ, some 2.1 features such as eARC can be made available on products with HDMI 2.0a connections via a firmware update (depends on manufacturer implementation). Also, new HDMI cables are not required for eARC — regular high-speed cables with Ethernet will do the trick.