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. Analogue connections for headphones, speakers 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?

HDMI also offers a function here: The Audio Return Channel has been available since HDMI 1.4. The usual structure of a home cinema system looks like this: media player > AV receiver (or soundbar) > TV set. The media player delivers picture and sound to the AV receiver, which outputs the sound and passes the signal on to the television. The television then basically only provides the picture. Nowadays, the apps of streaming services 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 traditional 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 convert the TV to ARC output. The internal speakers usually switch off. The sound from the app or the internal television tuner is then output from 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. Some desired configurations do not work as hoped. The device manufacturers and content providers just don't write about what isn't 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 on multiple channels. The German sound is then only stereo.
  • The media libraries of the public broadcasters also only provide stereo ( that is currently changing! ). Although Dolby Digital is also used when receiving via satellite, antenna or cable.
  • YouTube has countless surround tests & trailers - but the YouTube app on most devices can only do stereo.
  • Always connect the HDMI output (not an input) of a sound system, HDMI audio extractor or switch with the HDMI input of the TV. ARC is just 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 TV transmits a control signal via HDMI-CEC to the sound system and instructs it to change the volume. That's why on many televisions the ARC function is only possible when 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 sound
DTS 2.0 or 5.1 sound
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. Only TVs from LG and Samsung have been able to do it since around 2016. Officially, HDMI 2.1 is the only way to do this eARC (enhanced Audio Return Channel) such higher sound formats (see below).

ARC when using additional HDMI components

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

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

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

Difference from SPDIF Digital Audio

Compared to a digital audio connection via SPDIF (Toslink or Coax), the HDMI ARC has the following advantages:

  • Lip-sync function for automatically synchronizing image & sound
  • Support for Dolby Digital Plus (with Dolby Atmos, only on latest devices)
  • Control the volume via TV remote control via HDMI-CEC

At this point we do not want to hide the fact that in practice compatibility problems with the ARC are much 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, for 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 television 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 DTS passthrough

Sometimes there is a problem that DTS sound is not transmitted, especially with new LG and Samsung televisions. The TV manufacturer suppresses the transmission because it cannot be played via internal speakers due to the lack of a decoder. Sometimes it will at least be played in stereo.

DTS formats can only be found on Blu-Ray discs. There are two options for listening to such media with multi-channel sound:

1. Either output the sound already decoded (many Blu-ray players and also the Xbox or Playstation can do this). The game consoles have an additional menu, which only appears when a Bluray is inserted and allows different audio settings. If you set that DTS is not supported by the sound system, it will be decoded as PCM5.1 or PCM7.1. This is almost lossless, only DTS-X metadata is omitted.

2. 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 a single HDMI output on the player, the signal can be distributed, for example with the FeinTech VAX01203 orVSW04202 .

Advantages 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 with Atmos

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

Do I need eARC for the best sound?

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

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

This doesn't work directly. Because HDMI-ARC is an addressed point-to-point connection and only a single sound system is intended. The television cannot address two systems, no matter what you switch between. The sound would also rarely be in sync. Presumably, such a scenario was not taken into account when developing the HDMI standard. What can you do?

  • Via 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 tuner, but from an external box (satellite receiver, Apple TV, Fire TV or similar), the audio signal can be distributed before it gets to the TV. A splitter like this is suitable for this VAX01203 . Or a matrix switch like that VMS04201 . The sound system must have a real HDMI input in addition to HDMI-ARC.
  • A few televisions can output sound via HDMI-ARC and the optical output at the same time. Unfortunately, such models are now rare.