Intro
HDMI cables are widely used in home theaters for their convenience in delivering both audio and video through a single cable. However, it’s important to note that HDMI standards and their associated features differ across versions. Each new HDMI version introduces advancements which have specific benefits depending on your setup. Understanding how these features work can help you maximize the potential of your system. Two of these advancements on the audio side have been HDMI ARC and HDMI eARC. In this post, we take look at these audio features, their functionality, and methods for identification.
What is HDMI?
HDMI stands for High-Definition Multimedia Interface, and it is a proprietary D-shaped audio/video interface that can transmit uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device to a compatible display device, such as a monitor, projector, or TV.
HDMI was developed by a group of electronics manufacturers in 2002, with the goal of creating a universal standard for connecting devices and improving the quality of high-definition content. HDMI 1.0, released in December 2002, supported a maximum video bandwidth of 3.96 Gbit/s (1080p/60 Hz or UXGA) and 8 channel LPCM/192 kHz/24-bit audio.
Since then, HDMI has evolved through several versions, each adding new features and capabilities, such as higher resolutions, deeper colors, faster refresh rates, dynamic HDR, enhanced audio capabilities like Audio Return Channel (ARC) and enhanced Audio Return Channel (eARC).
What is ARC?
HDMI ARC (High-Definition Multimedia Interface Audio Return Channel) was introduced with the HDMI 1.4 specification in 2009. It was designed to simplify audio connections by eliminating the need for additional cables between the TV and the AV receiver or active speaker system.
Before HDMI ARC, audio from a display had to be transmitted using separate audio cables. This was not an issue when TVs were only used for display purposes and only had one input. However, with the rise of smart TVs and TVs with multiple inputs, where the TV itself became the audio source and input switcher, it soon became inconvenient to route audio cables as well as video cables to and from the AV Receiver or active speaker system.
HDMI ARC solves the issue of transmitting audio from the display back to the sound processor using the same HDMI cable used for video. It allows for audio playback regardless of whether the audio originates from the display or the AV receiver. This means that the display can function as an audio source device connected to the receiver.
An example use case is when you play Netflix on your Smart TV and want the audio to come from your AV Receiver instead of the TV’s own speakers, HDMI ARC eliminates the need for extra cables like optical or RCA. You only need an HDMI cable connecting the sound device and TV with HDMI ARC ports on both devices.
Additionally, HDMI ARC allows you to control your sound device using the remote of the display, called CEC (Consumer Electronics Control). This feature adds convenience to your home theater setup by eliminating the hassle of managing multiple remotes.
Every HDMI device is required to support the fundamental stereo audio format, which is uncompressed and in pulse code modulated (PCM) format. Optional audio formats are available as well, enabling the transmission of uncompressed audio with up to 8 channels. These formats support bit-depths of 16, 20, or 24 bits, and sample rates ranging from 32kHz to 192kHz.
HDMI ARC Limitations
The challenge with ARC is that manufacturers have the freedom to select which elements of the protocol they want to incorporate. It is not mandatory for all relevant audio codecs to be supported, meaning you cannot assume that a TV will be capable of transmitting a 5.1 Dolby Digital or DTS soundtrack from a movie over ARC. Certain TV manufacturers may only support Dolby Digital, while others may only offer two-channel stereo, which undermines the intended functionality.
ARC does not support high-bitrate codecs like Dolby TrueHD, Dolby Atmos, DTS-HD Master Audio, or DTS:X, which are commonly found on Blu-rays and 4K Blu-rays. Instead, it only extracts the core 5.1 data stream. If you desire this level of functionality, HDMI eARC is required.
However, some streaming services like Netflix, Disney Plus, and Amazon Prime can embed Dolby Atmos in the lossy Dolby Digital plus format that ARC can handle. So it is important to understand how your system will be used.
What Do You Need for HDMI ARC?
You will need to have an HDMI cable and devices that are spec’d to have HDMI version 1.4 or higher. Note, each device and cable in the chain will have to be ARC compatible for the feature to work properly. Today it is very common to find an HDMI cable that is spec’d to at least HDMI 1.4 but be sure to check the cable before you buy.
For the device, you want to check in the owners manual to make sure that the manufacturer has included an HDMI ARC port. You can also check directly on the device, as it is often labeled next to the ports, see picture below.
Note: Not all ports will have ARC/eARC capability, it is usually on only one or two ports.
What is eARC ?
HDMI eARC stands for High-Definition Multimedia Interface Enhanced Audio Return Channel. It is an upgraded version of HDMI ARC that offers the same functionality as well as several advantages over its predecessor and was introduced in November 2017 with HDMI 2.1.
First, the number of supported audio channels increased from 8 to 32, while keeping the max sample rate of 192kHz per channel. This allows HDMI eARC supports higher bandwidth and faster data transfer, which means it can handle more advanced audio formats, such as Dolby Atmos, DTS:X, and LPCM. This means that the Blu-ray discs and some streaming services will be able to playback full master quality audio if available.
Also, HDMI eARC also has improved lip-sync correction and device compatibility, making it easier to connect and switch between different sources.
What Do You Need for HDMI eARC?
For HDMI eARC, you will need a cables and devices that support the feature. Just like HDMI older specifications of HDMI , inclusion of features is not mandatory. Therefore, it is crucial to verify that your cables and devices support the eARC features you desire. Generally, HDMI cables/devices labeled as HDMI 2.1 and above are a reliable choice.
The adoption of eARC-compatible devices is growing more widespread as spatial audio formats gain popularity. Previously, this feature was predominantly available in premium models.
Remember, all devices and cables within the signal chain must be HDMI eARC compatible for the feature to function properly. For instance, if your TV supports eARC but your AV Receiver or soundbar only supports ARC, you won’t be able to fully utilize the advantages of eARC, as the bandwidth will be limited to ARC capabilities.
HDMI ARC/ eARC Comparison Table
Into the Future
The HDMI standard has allowed for the simplification of audio and visual data transition from device to device. HDMI cables are consistently evolving and adding more and more features. However, due to the voluntary nature of the standard, it’s hard for the average consumer to navigate if a certain cable or device will work. So it a good idea to read all the specifications of the cable/device before you purchase it. My hope is that the HDMI spec, becomes easier for the consumer as time goes on.
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