ARC – der Audio Rückkanal von HDMI - FeinTech

ARC - the audio return channel of HDMI

Why ARC?

Many users have already noticed that the connections on current television sets are becoming fewer and fewer. Analog connections for headphones, loudspeakers or stereo systems are frowned upon. With HDMI there is a universal solution for digital signal transport for the TV - but how do I send the TV sound to a sound system?

Here, too, HDMI offers a function: Since HDMI 1.4 there has been the Audio Return Channel (audio return channel). The usual structure of a home cinema system looks like this: media player > AV receiver (or soundbar) > TV set. The media player delivers picture & sound to the AV receiver, which outputs the sound and forwards the signal to the television. In principle, the television only provides the picture. Nowadays, streaming service apps such as Netflix, Amazon Prime, Maxdome or Dazn play an important role. These offer 5.1 sound or even Dolby Atmos much more often than conventional television broadcasts. For playback, the sound can be transmitted in the opposite direction via HDMI. The signal path is then from the television to the AV receiver. To do this, the television uses the same wires in HDMI cables as in normal operation. The signal direction must therefore be switched. As a rule, only one of the TV HDMI sockets can do this; it is labeled ARC.

The next step is to switch the TV to ARC output. Most of the time, the internal speakers switch off. The sound of the app or the internal TV tuner is then output at the HDMI ARC socket and transmitted to the sound system. This then plays the sound – also multi-channel.

pitfalls in practice

Unfortunately HDMI is more complicated to use than expected. Many a desired configuration does not work as hoped. The device manufacturers and content providers do not write about everything that is not possible. Here are a few practical tips:

  • Streaming apps like Netflix or Amazon Prime like to list the available sound formats for films and series. They often forget that only the original sound is delivered in multiple channels. The German sound is then only stereo.
  • The media libraries of the public broadcasters also only deliver in stereo. Although Dolby Digital is also used when receiving via satellite, antenna or cable.
  • YouTube has countless surround tests & trailers - however, the YouTube app on most devices only supports stereo.
  • Always connect the HDMI output (not an input) of a sound system, HDMI audio extractor or switch to the TV's HDMI input. ARC is only the return channel for the sound, the main signal direction is reversed.

Digital audio signals have no volume information. It is therefore no longer possible to control the volume directly with the TV remote control. Instead, the television transmits a control signal to the sound system via HDMI-CEC and instructs it to change the volume. For this reason, the ARC function is only possible with many televisions when the CEC is active. (Manufacturer names for CEC are Simplink (LG), Bravia Sync (Sony), Anynet+ (Samsung), VieraLink (Panasonic), etc.

Sound formats via ARC

The following formats can be transmitted via ARC.

format Contents
Stereo 2.0 (uncompressed)
Dolby Digital / AC3 2.0 or 5.1 audio
DTS 2.0 or 5.1 audio
Dolby Digital Plus / eAC3 / DD+ 2.0, 5.1, 7.1 sound or Dolby Atmos

Most televisions cannot yet output DD+ via ARC. Because that wasn't part of the original specification. Officially, only HDMI 2.1 allows with the eARC (enhanced Audio Return Channel) such HD sound formats (see below).

ARC when using other HDMI components

If you have active HDMI cables or repeaters are used, they must also explicitly support the ARC! Such signal amplifiers otherwise prevent the backflow of the audio signal. HDMI splitter typically do not support ARC. Because HDMI-ARC only works with many televisions together with CEC communication. A television communicates with a sound system and the sources. At CEC, however, there may only be one television and one sound system, nothing more is specified. When operating two televisions in an HDMI chain, there are otherwise unforeseeable malfunctions.

Even with an HDMI switch or matrix switch , the ARC function is rare. If present, there is always a button labeled ARC for switching the signal direction.

Incidentally, you can also use ARC as a pure HDMI audio output and only connect a soundbar to it. With help of a HDMI audio extractors you can also just pick up the sound. Note, however, that ARC audio is always digital and is not simply played on an analog stereo system. So you have to use a digital audio connection.

Difference to SPDIF Digital Audio

Compared to a digital sound connection via SPDIF (Toslink or coax) the HDMI ARC has the following advantages:

  • Lip-sync function for automatically synchronizing picture & sound
  • Dolby Digital Plus support (with Dolby Atmos, latest devices only)
  • Control volume by TV remote control through HDMI-CEC

At this point, however, we do not want to hide the fact that in practice, compatibility problems with the ARC are far more common than with SPDIF connections. This is due to the complex communication between the devices and the large number of possible formats.

The eARC of HDMI 2.1

The new HDMI 2.1 standard provides an extended ARC. That's why it's called enhanced Audio Return Channel, short eARC . This is also an audio return channel that delivers the sound in the opposite direction to the HDMI signal direction. The HDMI input a TV provides an eARC audio signal. The internal TV sound (e.g. satellite TV or smart TV app) is output to a sound system. When a TV's eARC is active, the internal speakers typically remain silent. But the sound of other players connected to the TV can also be passed through.

No passthrough of DTS

Sometimes there is the problem that DTS sound is not transmitted, especially with new LG and Samsung TVs. The transmission is deliberately suppressed by the TV manufacturer. Stereo or a Dolby format is used instead. DTS formats can only be found on Blu-Ray discs. There are two options for listening to such media with multi-channel sound: Either output the sound already decoded (many Blu-ray players and the Xbox can do this). Or don't use an HDMI-eARC connection and instead transmit the sound separately. This works if the sound system has at least one “real” HDMI input. Either the second HDMI output of the Blu-ray player can be connected there. If there is only one HDMI output on the player, the signal can be distributed, eg with the FeinTech VAX01203 orVSW04202 .

Benefits of eARC

The eARC has more bandwidth than ARC and supports additional audio formats:

format Contents
PCM 5.1 / 7.1 uncompressed 5.1 and 7.1 sound*
DTS HD High Resolution Audio compressed 5.1 or 7.1 sound**
DTS HD master audio uncompressed 5.1 or 7.1 sound**
Dolby TrueHD uncompressed 5.1 or 7.1 sound*
Dolby MAT uncompressed 7.1 sound*

*may contain Dolby Atmos metadata for 3D sound
**may contain DTS:X metadata for 3D sound

Do I need eARC for best sound?

No, HDMI-eARC is only required if external players are to route HD audio formats through the television to the connected sound system.

My TV only has one HDMI-ARC / HDMI-eARC connection. But I would like to run 2 sound systems on it. How does it work?

That doesn't work directly. Because HDMI-ARC is an addressed point-to-point connection, and only one sound system is intended. The television can therefore not address 2 systems, no matter what is switched in between. The sound would also rarely be synchronous. This is probably why such a scenario was not considered when the HDMI standard was developed. What can you do?

  • About our adapter VMA00201 a soundbar with HDMI-ARC in Dolby Digital 5.1 and headphones in stereo can be operated at the same time.
  • If the sound does not come from the TV from apps or a tuner, but from an external box (satellite receiver, Apple TV, Fire TV or similar), the audio signal can be distributed before it reaches the television. A splitter like this works well for this VAX01203 . Or a matrix switch like that VMS04201 . In addition to HDMI-ARC, the sound system must also have a real HDMI input.
  • A few televisions can output the sound via HDMI-ARC and the optical output at the same time. Unfortunately, such models are now rare.