More about ARC

Created on 2012-11-08 00:48:00

APx support of HDMI versions and features

APx HDMI modules fully support HDMI version 1.3a. The APx HDMI+ARC module adds ARC (Audio Return Channel) support, which is a subset of the HDMI 1.4a specification. Other HDMI features added in 1.4a are not supported. In the APx implementation, ARC Tx (transmit) and ARC Rx (receive) input and output selections are entirely independent of the standard HDMI audio configuration and features. The ARC Tx signal appears on the connector also used for HDMI AUX IN, and the ARC Rx uses the connector also used for HDMI AUX OUT.


About ARC

ARC (Audio Return Channel) is a feature of HDMI 1.4a that enables digital audio (IEC 60958 / SPDIF) transmission and reception on existing but previously unused conductors in standard HDMI connectors and cables.

ARC was added to eliminate the need for a coaxial or optical digital cable to return audio from a device designated as an HDMI sink. The classic case is a television (typically connected as a sink to a home theater receiver acting as a video source) that has been configured to receive video directly from an RF antenna, rather than from the receiver. The audio from the on-air signal must be routed to the receiver; in the past this required an additional cable. The HDMI ARC function designates existing conductors in the HDMI cable to act as a digital audio return channel, presenting the audio to the source connector on the receiver.


Physical Layer

The ARC digital audio signal is carried on a twisted pair of wires in an HDMI cable. These wires are designated HEAC+ and HEAC-. The ARC signal can be carried in two modes. In Single Mode, the digital audio signal is carried on the HEAC+ conductor, relative to the HDMI ground. In Common Mode, the ARC signal is carried commonly on the HEAC+ and HEAC- conductors, relative to ground. Common mode facilitates an HDMI 1.4a feature not supported by APx, carrying an ethernet signal simultaneously in differential mode on the HEAC- and HEAC+ conductors.



CEC is an HDMI protocol that provides high-level control functions between all of the various audiovisual products in a user’s environment. In general, the APx500 implementation does not utilize CEC, except to allow or disallow forwarding of DUT CEC to downstream devices, when input is set to HDMI sink.

In HDMI+ARC, CEC and EDID are necessary for ARC link negotiation. APx can be set to negotiate the ARC link, or to force audio data ON regardless of link authorization. A CEC Message dialog is available from the settings dialogs to send specific ARC-related CEC messages manually for diagnostic purposes.