HDMI 2.1 ARC/eARC audio return capability

For audio and video and game enthusiasts, the experience of pure picture is far from enough. If watching Blu-ray blockbusters and playing 3A masterpieces, the immersion is greatly reduced by the weak performance of TV speakers alone, so more and more people are also pursuing echo walls and home theaters that can decode Dolby Atmos and DTS:X next-gen audio.

The numerous interface versions of HDMI and the less-than-perfect compatibility between devices from various manufacturers (especially eARC) lead to various problems in connecting game consoles/Blu-ray players to TVs and home theaters.

In this article, the purpose, principle and and usage of the ARC and eARC functions in HDMI 2.1 will be described in detail.

I. What is the ARC/eARC audio return function?
1.1 ARC audio return channel
ARC (Audio Return Channel) audio return function was introduced in HDMI version 1.4, the function is similar to the optical digital audio port (optical audio), bandwidth of about 1Mb, can return the audio format.

Dolby Digital 5.1, DTS 5.1, Dolby Digital Plus 5.1, LPCM 2.0
In other words, ARC can only transmit basic lossy (compressed) 5.1 channel audio tracks and lossless LPCM stereo audio tracks.

Does that mean that ARC can't light up Dolby Atmos?

Not really.

Dolby Atmos is not an audio codec, it is a format that describes the metadata of the sound information inside the TrueHD or Dolby Digital Plus track, which is commonly known as an object-based description file. It is an object-based description file that describes when and where the sound appears.

Therefore, when watching Dolby Atmos tracks encapsulated with Dolby Digital Plus 5.1 core, such as Nifty, HBO+ and other streams, the ARC port will still light up Dolby Atmos properly.

1.2 eARC Enhanced Audio Return Channel
eARC is the enhanced (Enhanced) ARC, a standard feature of the HDMI 2.1 interface. The bandwidth becomes 37Mb, finally allowing the transmission of next-generation lossless audio tracks:.

Dolby TrueHD, AC-4, Dolby Atmos, DTS HDMA, DTS:X, LPCM 7.1
In other words, the eARC channel eats all audio formats currently on the market, whether lossless or 32-channel.

There is one more propaganda trap about eARC!

Since the eARC data channel uses 14 and 19 ports in the HDMI interface, independent of the four high-speed data channels of HDMI 2.1, this feature can be downlinked to the HDMI 2.0 interface.

We generally refer to the HDMI interface with a transmission bandwidth of ≥ 40Gb as the HDMI 2.1 interface, but there are many manufacturers of devices with a bandwidth of only 18Gb, which is actually the HDMI 2.0 interface, but because it is equipped with the eARC function as the HDMI 2.1 interface publicity, such as Philips B97 Echo Wall, you must do your homework when buying.

As of July 15, the world has not yet a real echo wall with HDMI 2.1 interface (strip home theater).

Second: does the optical HDMI cable support ARC/eARC audio return?
First to the conclusion: support, but generally need to be within 15 meters.

As you may know, the fiber optic HDMI cable is directional, the interface at both ends of the cable, a Source (source) port, a Display (display) side, that since the signal can only flow from the source side to the display side, how to achieve the audio return?

In fact, the optical HDMI cable is not the entire HDMI cable is optical fiber, but only four high-speed data channels using optical fiber, the rest of the low-speed channels or copper, such as DDC (EDID), and ARC/eARC channels, see the following figure.

This is a fiber optic HDMI cable interface disassembly diagram (send side), you can see that only four fiber optic cable is connected to the photoelectric conversion chip, while the copper cable is directly connected to the jack.

In other words, the optical HDMI cable, in fact, only the four high-speed data channels are directional, while ARC and eARC using copper wire, and no directional, so support audio back.

So why do some brands of fiber optic HDMI cable but claim that they do not support ARC and eARC?

In fact, or the reason for the distance.

General fiber optic cable, 5 meters to start with, the longest can reach 300 meters. Fiber optic anti-interference ability, low loss, even 200 meters signal is still very strong; but copper cable is not the same, more than 15 meters, if the general material, shielding is not well done, then the audio digital signal attenuation is serious, may be to the amplifier and echo wall distortion is very serious, basically unusable.

Therefore, if you buy fiber optic HDMI cable requires eARC function, be sure to ask before you buy, how much distance the eARC function supports.

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