“It was noted in Section 5 that HEAC is a standard rather than optional feature in Category 3 cables, but its primary function changes to that of being the transport for the Enhanced Audio Return Channel (eARC). This is depicted in figure 5.2 (page 5), which shows the shared HEAC/eARC transport pins.

With no physical or electrical change to HEAC, any existing Standard with Ethernet, High Speed with Ethernet, or Premium High Speed with Ethernet cable will be compatible for use with the full feature set and capability of eARC. In fact, these cables should theoretically perform equally well for supporting eARC as any new Ultra High Speed HDMI cable.

However, one caveat to consider is that HEAC has not historically been subject to performance testing in determining compliance. HDMI 2.1 does define an eye diagram specifically for an eARC transmitter, setting the bar for its performance, but it remains to be seen if this will extend to electrical performance and compliance testing of this channel in the cable.”