The long-awaited HDMI 2.1 specification was finally released on November 28, 2017, which we covered here. Among its improvements over HDMI 2.0 is eARC (Enhanced Audio Return Channel), which offers far more capability than the original version of ARC. Lattice Semiconductor saw the importance of eARC immediately and unveiled transmitter and receiver chips shortly after the HDMI 2.1 spec was released.
ARC was first implemented in HDMI 1.4. As you may know, it allows an HDMI receiving device, such as a TV, to send audio information to an HDMI transmitting device, such as an AVR or soundbar, back along the same cable that otherwise carries AV data from the transmitting device to the receiving device. This is especially important for so-called “smart TVs” with built-in streaming apps. It allows them to send the audio from the streaming content to an outboard audio system without having to connect a separate cable, typically optical digital audio, from the TV.
Without ARC, audio from a TV’s internal tuner or streaming apps is sent to the outboard sound system with a separate cable. With ARC, the audio is sent to the sound system along the same HDMI cable that conveys AV data to the TV.
However, ARC is fairly limited. With a maximum data rate of about 1 Mbps, it supports 2-channel and compressed 5.1-channel audio, but not uncompressed 5.1 or 7.1. It offers optional lip-sync compensation, but few products implement it.
In addition, ARC is integrated with CEC (Consumer Electronics Control), which conveys commands to connected HDMI devices in order to control them from one remote. This allows ARC to “discover” the capabilities of connected audio devices, but if a user disables CEC—which many do because it can lead to some unwanted behavior—ARC will not function at all.
By contrast, eARC has a maximum data rate of 37 Mbps, allowing it to support uncompressed multichannel and immersive audio, including up to eight channels at 192 kHz/24 bits. In addition, lip-sync compensation is mandatory, and eARC can discover connected audio devices and ascertain their capabilities using its own data channel. If CEC is turned off, eARC will continue to work.
To support such high performance, eARC uses the twisted pair of wires within an HDMI cable normally used for Ethernet over HDMI. Of course, Ethernet and eARC can’t be used at the same time, but this doesn’t seem like a real problem to me. I’ve never understood why anyone would want to send Ethernet data over HDMI anyway. The Ethernet channel supports a data rate of 100 Mbps, so eARC’s 37 Mbps is a breeze.
HDMI 2.1 has not yet been implemented in consumer products, but that hasn’t stopped Lattice from developing eARC transmitter and receiver chips. These chips operate in conjunction with a device’s HDMI transmitter and receiver chips. The new eARC chips are fully backward compatible with ARC, so they can be used with current HDMI transceivers, but they are ready to provide full eARC functionality when HDMI 2.1 transceivers become available.
Lattice Semiconductor’s eARC transmitter and receiver chips are used in conjunction with HDMI transceivers to send high-quality audio from the receiving device (say, a TV) back to the transmitting device (say, a soundbar or AVR).
According to Marshall Goldberg, marketing manager at Lattice Semiconductor, “HDMI’s purpose is to deliver two promises to the consumer—provide the highest possible digital audio and video quality, and make it simple through automatic configuration. eARC technology is a tremendous step in home-theater connectivity, as it brings vastly higher audio quality than TosLink or S/PDIF, without the complexity of switching through an AVR device. In addition, its all-new discovery method guarantees compatibility when products from different manufacturers are connected in a home-theater system.”
Hopefully, independent compliance testing for HDMI 2.1 devices, including Lattice’s eARC chips, will become available in the first quarter of 2018. After that, we could start seeing consumer products with HDMI 2.1 and eARC, perhaps before the end of the year. That’s good news for AV enthusiasts, because eARC promises to simplify the use of AVRs and soundbars with TVs, improve compatibility and reliability, and future-proof HDMI products for many years to come.