In 2009, Audio Return Channel, or ARC functionality, was integrated into the HDMI 1.4 specification.
ARC stands for Audio Return Channel. It is a feature on some HDMI-enabled devices, such as projectors that allows audio to be sent "upstream" to an audio system or soundbar over the same HDMI cable used for video.
When manufacturers started introducing “Smart” enabled projectors and televisions featuring application-driven content services like Netflix, connections from the source, sound system, and display were in one direction. Getting audio from Netflix from a Netflix app installed on the projector back to the sound system was often not possible. And even if it could be done, the connections could present performance and compatibility problems.
Consumers could change the order of devices connecting all their sources to their smart displays. Still, running a jungle of AV wires into a projector or television would be an unsightly nightmare.
ARC solved these problems by including a dedicated audio channel in the HDMI cable, called the HDMI-ARC channel. This channel allows the projector to send audio signals to the source device, such as a cable or satellite box, and for the source device to send audio signals back to the TV or projector. ARC eliminates the need for a separate audio cable between the source device and the audio system/soundbar, such as a TOSLINK or Coaxial cable.
With ARC, customers can enjoy PCM 2-Channel, Dolby Digital (up to 5.1 channel), and DTS Digital Surround (up to 5.1 channel) audio formats.
ARC and Dolby Atmos compatibility is more complicated. The ability to pass a Dolby Atmos signal depends on the type of HDMI connection your projector and audio device supports.
ARC does not support any lossless audio codecs with lossless compression. For these, you need eARC.
ARC also supports HDMI CEC, simplifying control of components in the connected chain of devices (projector, sound system, and sources). CEC is a channel that controls input, power on and off, volume, play, pause, etc., of compatible HDMI devices using a single remote control.
It is up to individual manufacturers to decide what HDMI features, including ARC, work on their devices. HDMI-enabled projector, receiver, or source device says that it supports ARC, but this device does not support all of ARC. Users should look carefully to determine what ARC capabilities devices support before purchasing.