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HDMI 2.1 - The Definitive Guide to the Next Generation | Audioholics

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HDMI 2.1

The HDMI 2.1 specification has been in use for some time, first of all

. The new specification is the result of an impressive effort made by the HDMI Forum, an open trade association dedicated to promoting "a wider industry to participate in the development of future versions of the HDMI specification and to further expand its ecosystem"). Interoperable products that support HDMI. "The members of the forum include many of the world’s leading consumer electronics manufacturers, as well as testing laboratories, film studios and other institutions. They are trying to develop a new HDMI standard that should have basic future-oriented capabilities ( Or-at least foreseeable). Until the end of 2020, with the emergence of the first HDMI 2.1 source component, the team’s design work and plans will finally be realized, and this component will be added to more and more existing or upcoming List of HDMI 2.1 audio components and displays on the market, finally, home users can assemble a complete HDMI 2.1 gear chain.

What's all the fuss about? In short, bandwidth. HDMI 2.0b (the predecessor of 2.1) can reach a maximum bandwidth of 18 Gbps (gigabits per second). Just a few years ago, this was a good sum of money, but the AV signals generated by today's game consoles and 4K Blu-ray players may almost consume space in the road. These devices provide 4K video at up to 60 fps (frames per second). Currently, the only source capable of outputting 4K video at 60 fps or higher is a high-end gaming PC. But by the end of this year, we will begin to see sources that can provide 8K video at 60 frames per second or 4K video at a smooth rate of 120 frames per second. In order to support higher resolutions and higher frame rates as well as some useful new features, HDMI 2.1 provides a bandwidth of up to 48 Gbps. In addition to allowing higher resolution and higher frame rates to provide smooth, fast motion details, this additional bandwidth will also support dynamic HDR, ensuring that every moment and color of the video content is displayed with the ideal combination of brightness and contrast . HDMI 2.1 also improves the audio experience and simplifies system connections through a feature called eARC or an enhanced audio return channel. eARC ensures compatibility between AV devices, while supporting the most advanced audio formats available and the highest quality audio signals. (More information about eARC at the end of this article.)

It is almost certain that the first two source components that support 8K at 60 fps and 4K at 120 fps will be Sony’s upcoming Playstation 5 and Microsoft’s new Xbox Series X, both of which are planned to be available in the 2020 holiday season. Not surprisingly, these cutting-edge game consoles should be the first HDMI 2.1 source, especially when you consider some of the enhanced gaming and media features included in the new specifications-many of them focus on smooth motion and/or reduced input Lag.

I will introduce these features in more detail in the short term, but it is worth pointing out that even if you are not interested in the game, you may find one or more of them useful.

At the 2020 International Consumer Electronics Show (CES 2020), there are 8K TVs everywhere, and the ability to transmit 8K signals at a refresh rate of 60 Hz is one of the most concerned features of HDMI 2.1 video functions. To be fair, if you have the opportunity to see LG’s Signature ZX 88-inch 8K OLED TV, you will definitely be impressed, with its horizontal and vertical resolutions twice that of a 4K display and four times the pixels ( More than 33 million). But the reality is that there is almost no 8K content at the moment, and few of us will upgrade to 8K TVs in the next year or two. Therefore, for most people, the real benefit of the video performance brought about by the increased bandwidth of HDMI 2.1 will be the ability to send 4K video at 120 frames per second, which is twice the frame rate provided by HDMI 2.0b. As Phil Jones of Sound United mentioned in a recent video interview with Audioholics founder Gene DellaSala, many gamers are excited to be able to play 4K games at higher frame rates because the smooth motion allows for smoother And play the game easily. The ability to display UHD images at 120 fps can also benefit certain movies and TV content, such as action movies, nature documentaries, and sports shows. Higher frame rates can provide clearer images, even in fast-moving scenes. Can also maintain clarity. Support the latest color space, such as BT.2020 (also known as Rec.2020), each color component has 10 or 12 bits. For commercial audio-visual installations and industrial/professional use, HDMI 2.1 can support other resolutions, including 5K or even 10K. 

If you are a technical expert in video transmission, you may want to know whether compression is used in the HDMI 2.1 specification to achieve these high resolutions and frame rates. The short answer may be. The specification supports both compressed and uncompressed modes, and each manufacturer decides which mode to implement. However, even with compression, the specification includes VESA DSC (Display Stream Compression) 1.2a, which is a visually lossless compression scheme. At 60 fps, all videos with resolutions and frame rates higher than 8K require DSC, but this is not important for home users. In order to obtain a higher uncompressed resolution than HDMI 2.0b (that is, higher than 4K at 60 fps), the HDMI 2.1 specification uses a new signaling technology called FRL (Fixed Rate Link). This technology replaces the TMDS (Minimized Conversion of Differential Signals) used in early versions of HDMI, but HDMI 2.1 is backward compatible with devices using TMDS, so for home users, the conversion should be seamless and painless.

Most modern displays (TVs or projectors) cannot fully utilize the maximum potential image quality provided by the 48 Gpbs bandwidth of HDMI 2.1. why? Currently, LCD and OLED panels used in high-end consumer TVs are native 10-bit panels. To transmit 4K chroma 4:4:4 and 10-bit 4K video at 120 fps, 40 Gpbs is required. To transmit 8K images with 10-bit color at 60 fps, a maximum of 40 Gpbs (uncompressed) is also required. (If DSC compression is applied, the necessary bandwidth will be reduced to 18Gpbs.) For example, all of LG's 2020 OLEDs have HDMI 2.1 ports, but they are limited to 40 Gbps instead of 48 Gbps of bandwidth. But because they use native 10-bit panels, 40 Gbps is enough to maximize the panel's functionality. Due to the limitations of these panels, in any case, 40 Gbps can now be regarded as the maximum bandwidth required for actual scenarios.

Many experts agree that the most significant improvement in video quality achieved in the UHD era is not the inherent high resolution of 4K video, but the emergence of high dynamic range (HDR). With HDR, video content can provide a greater range of contrast from dark to light, resulting in a high-impact experience. The result is that the light and dark parts of a given image have brighter whites, darker blacks, and improved details. This improved contrast, combined with more detail in the expanded color space, helps provide a more intrinsic video experience. The HDR solution can be static (meaning it uses a set of metadata to optimize the image brightness curve of the entire video), or dynamic, which means it uses dynamic metadata to optimize the brightness of the image scene by scene or even frame by frame. . Frame by frame. Static HDR solutions (such as HDR10) and dynamic HDR solutions (such as Dolby Vision) can be delivered on previous HDMI versions, but the HDMI 2.1 specification supports a variety of static and dynamic HDR solutions to ensure that dynamic metadata is not used in the future. It must be bound to a proprietary format (such as Dolby Vision), which requires the manufacturer to pay a license fee. HDR-enabled devices that implement HDMI 2.1 will transmit static and dynamic HDR metadata through the HDMI interface in a standardized way to ensure that the metadata will be delivered correctly regardless of the manufacturer of the product. To ensure that users will get all the benefits of dynamic HDR without compatibility issues, all HDMI 2.1 devices must undergo the same mandatory compliance testing.

As mentioned earlier, the HDMI 2.1 specification includes many features designed to improve the gaming experience, including variable refresh rate (VRR), automatic low latency mode (ALLM), fast media switching (QMS) and fast frame transfer (QFT). . I will now give a more in-depth introduction to these features to explain their full meaning and how they can benefit non-gamers as well.

VRR aims to reduce or eliminate lag, jitter and frame tearing, thereby making the game process more smooth and detailed. But what does this mean? When you play a video game, the graphics processing unit (GPU) in your computer or game console will render the image faster or slower based on what is happening on the screen and the processing power available. But traditionally, the refresh rate of a TV or monitor is static, which means it will never deviate from the specified frequency (for example, 60 Hz). It doesn't matter whether the GPU needs more time to render a particular frame in a particularly complex scene-this happens often, depending on the power of the GPU and the selected resolution-the display refreshes when it refreshes. If the GPU has not finished rendering the next frame before the display is refreshed, the GPU must repeat the previous frame or send an incompletely rendered frame. result? Occasionally there will be a "tear" picture, which will bring a long-lost jury experience. VRR solves this problem by allowing the source and display to work together and changing the refresh rate as needed. The GPU can wait until the next frame is ready before sending it to the display, and the display can wait to refresh until the next frame is received. By synchronizing the refresh rate of the display with the refresh rate of the content generated from the source, the gaming experience will become smoother and more direct. At any given time, the refresh rate may be in any range between 30 Hz and 120 Hz, depending on the burden of the GPU at this time. If you are not a gamer, you might think that VRR has nothing to do with your needs, but that is not the case. Facts have proved that many Web-based video content end up with abnormal frame rates, which may be because it is produced using a variety of non-standardized hardware and software combinations. So if you like watching YouTube and other Internet content (and not who?), you might benefit from VRR because your TV will be able to display the content at its original frame rate.

The automatic low-latency mode is relatively simple. Many TVs (and some AV receivers, such as recent Denon and Marantz models) have a low-latency mode or "gaming mode" that reduces input delay-the time the TV or monitor actually displays the signal has been received. If you are playing a video game, input lag may be the main part of the delay experienced between pressing a button on the controller and seeing the character/game reacting on the screen. In some competitive online game scenarios, a short lag time will give you an advantage over other players. This is like extending your own personal reaction time, which is essential for both gamers and athletes. But before using ALLM, you must manually set the TV to game mode (by entering the menu system) before playing games, and then manually set it to the normal environment when you want to watch TV or movies. (Since the low-latency mode reduces input lag by cutting into the image processing point, the resulting image quality is not optimal for normal viewing.) The automatic low-latency mode allows game consoles, PCs or other devices to transfer to the following devices Send signal: automatically turn on the TV in low-latency game mode. When the signal source no longer needs to reduce latency-suppose you stop playing games on the PS5 and then use the console to play a movie-the signal source will disable the signal and the TV will return to its normal settings for the best picture quality. Once again, this player-centric feature may prove useful for non-gaming activities, such as video conferencing (which is becoming more and more important during the coronavirus pandemic), or even karaoke.

Therefore, ALLM aims to reduce the lag time inside the TV, that is, the time it takes for the TV itself to display the received image. Fast frame transmission is also designed to reduce latency, but it is not something related to the settings in the TV, but a system inside the HDMI cable that reduces the time required for video frames to pass from the original source device (such as a game console). Or a PC, and then connected to a display device-it can be a TV, a computer monitor or a virtual reality headset. The delay mentioned here is called "display delay". This term refers to the total time required to fully render and ready to leave the GPU and then through the output circuit of the signal source, through the downstream of the cable, into the display, through the processing circuit of the display, and finally through the following steps: display on the screen . QFT transmits each frame at a higher rate to reduce the overall display delay, thereby further improving the snapshot speed, response speed, and providing real-time interactive virtual reality.

Fast media switching is designed to solve a specific problem. Suppose you are watching a movie trailer through a streaming service. It is not uncommon for different trailers to use different frame rates (such as 60 Hz, 50 Hz or 24 Hz). Similarly, many streaming media devices (Roku, AppleTV) use 60Hz for their menus, but movies use 24Hz as the frequency. When switching from one frame rate to another, all devices in the HDMI connection chain must change their clocks and re-synchronize, resulting in an instantaneous interruption called "bonk". Before the content is finally displayed, the viewer's TV screen will turn black. QMS uses the VRR mechanism to allow these frame rate changes without interrupting the viewing experience. The entire system can be quickly and smoothly changed from 60 Hz to a lower frequency, down to 24 Hz, without being clumsy.

Unlike the previous version of the HDMI specification, the 2.1 specification includes a new cable called the "Ultra High Speed ​​HDMI Cable", which is the first cable defined by the HDMI Forum. This new cable is "the only cable that meets strict specifications and is designed to ensure support for high-resolution video modes (including uncompressed video).


) And all other HDMI 2.1 features", according to the HDMI Forum. The increased bandwidth capacity of the cable can support up to 48 Gbps. Although the specification does not specify the length of the cable, the passive cable may reach a maximum of about 3 meters before the bandwidth starts to drop. The new cable will also “exceed the requirements of the latest international EMI standards to significantly reduce the possibility of interference with wireless services such as Wi-Fi.” All ultra-high-speed HDMI cables must pass the mandatory ultra-high-speed HDMI certification program, which includes Test conducted at the HDMI Forum Authorized Testing Center (ATC). The certification program is designed to ensure the quality and functional support/compatibility of all ultra-high-speed HDMI cables put on the market. Qualified cables will be affixed with the official ultra-high-speed HDMI on the package Certification label, and the outer sheath of the cable will also be labeled.

Compared with HDMI 2.0b, the HDMI 2.1 specification provides more functions.

Send as much data as possible over the cable at one time. Therefore, in order to take full advantage of HDMI 2.1, it is necessary to use a new ultra-high-speed certified HDMI cable. Indeed, in the end, you will need to upgrade to a newer cable to benefit from all of the above features. But the reality is that many people don't need all the new cables now to enjoy the most important features to them. Some of the most important functions in the specification, such as VRR, ALLM, eARC terminals, do not require new cables. This leads us...

In terms of audio, HDMI 2.1 mandates support for a function called eARC or Enhanced Audio Return Channel. As the name suggests, this is an updated and more powerful version of the HDMI ARC protocol, which was added to the specification table in 2009 and was introduced as part of the HDMI 1.4 version. Before introducing eARC in detail, let's take a review course on ARC. Before the advent of ARC, the HDMI cable was a one-way path for audio/video signals, which propagated from the source to the downstream, usually through the AV receiver or processor, and finally to the display. Consider the setup about ten years ago. My profile includes a Blu-ray player, a cable box and a Roku HD-XR ribbon. My roommate is a gamer, so I often connect to a game console. All these sources send their signals to my Denon receiver via HDMI cables, and then to my Pioneer TV. This is pretty typical and everything is fine. However, with the advent of smart TVs, things have become more complicated, and people have begun to use streaming media applications built into TVs as the main source of video content. In a setup like mine, even if the TV and receiver are connected via HDMI, the digital audio signal cannot be sent from the TV to the receiver via the cable. Doing so will require the signal to be transmitted "upstream" along a unidirectional HDMI cable. Therefore, in order to route the TV's audio to the AV receiver or soundbar, instead of the TV's internal speakers, a second cable is needed-almost always an optical Toslink cable. This not only adds another ugly cable to deal with, but also limits the sound quality. Some TVs can pass multi-channel audio signals to the receiver or soundbar via optical Toslink, but many other TVs only send stereo signals. (Today, only a few Sony TVs will send multi-channel surround sound signals via Toslink.)

In order to solve all these problems, the audio return channel function was created. ARC effectively turns HDMI into a two-way path, so that the TV can send audio back to the AV receiver, processor or soundbar via the HDMI cable. With ARC, in theory, it becomes easier to enjoy audio from TV streaming applications or antennas. Moreover, this also means (in theory) that you can choose to connect all HDMI sources directly to the TV instead of connecting to the audio device (if this is easier to set up). But ARC has its own limitations and problems. First, it sometimes runs automatically, and sometimes requires users to adjust various settings that may be included in the TV menu system. It also allows manufacturers to manually select which protocol elements they want to include and which ones to ignore. For example, some TVs can send 5.1 Dolby Digital or DTS audio tracks to the receiver via ARC, while other TVs still only support two-channel stereo audio tracks. Finally, ARC cannot deliver high-quality lossless codecs, such as Dolby TrueHD and DTS-HD Master Audio. If you connect a Blu-ray player directly to the TV via HDMI, and then try to use ARC to send audio to the receiver, at best you can only get a degraded data stream that relies on a lossy codec. Although ARC can theoretically support object-based immersive audio formats (such as Dolby Atmos) streamed from Netflix or Amazon Prime Video, they also rely entirely on lossy codecs (such as Dolby Digital Plus) instead of full Fat lossless version. ARC simply does not have the ability (or the required bandwidth) to handle uncompressed and lossless audio.   

The enhanced audio return channel aims to solve all the problems of ARC by improving the sound quality function while providing an easier-to-use way. With eARC, the original full-resolution audio signal can be sent "upstream" from the TV to the audio device. Dolby TrueHD, Dolby Atmos, DTS-HD Master Audio and DTS:X audio tracks can all be transmitted in real, lossless form. Due to the greatly increased bandwidth of HDMI 2.1, eARC can handle 32 channels of uncompressed audio, or up to 8 channels of 24-bit/192kHz audio. The audio processing power of the TV is no longer limited, because eARC requires an uncompromising approach to compatibility. Whether the audio signal comes from the TV’s internal application, or from a Blu-ray player or game console directly connected to the TV via HDMI, eARC will pass the full resolution sound signal back to the receiver, front/professional or sound. -bar.

Another benefit of eARC is that the technology integrates an improved "handshake" process between compatible devices. The original ARC protocol relied on HDMI CEC (Consumer Electronics Control), which usually had to be activated manually and did not always work properly. The new eARC standard eliminates the need to activate CEC, allowing users to get up and running without additional steps. This also means that users should be able to control various functions on various devices (such as turning on the power of the TV and then adjusting the volume of the receiver) without using multiple remote controls. The original ARC version should be able to use this function, but it was not ready before the emergence of eARC.

As mentioned above, eARC does not require a new ultra-high-speed HDMI cable. According to, both standard HDMI cables with Ethernet and high-speed HDMI cables with Ethernet can be used. Since using eARC's advanced audio format requires additional bandwidth, some very old (and/or very long) HDMI cables can be laborious, but before spending money on a new cable, be sure to try it with your current cable. The bad news is that some existing ARC-enabled products may not work with new products that use eARC. It is entirely possible for manufacturers to design products that are compatible with both ARC and eARC, but backward compatibility is not a necessary feature. In order for eARC to work properly, both the TV and audio equipment must have compatible HDMI eARC slots. The good news is that eARC (along with automatic low-latency mode and variable refresh rate) is not strictly limited to brand new HDMI 2.1 devices. These features are the most important part of the HDMI 2.1 specification. These features can be added to (or have been added to) certain HDMI 2.0 products through firmware updates. Some HDMI 2.0 TVs launched in 2019 and early 2020 have been updated to support eARC, and AV receivers of Onkyo, Pioneer, Sony, Denon and Marantz have also been updated.

There must be a lot of information in the HDMI 2.1 specification that needs to be unraveled, but the main takeaway is that the specification will provide improved audio and video and a better user experience. Considering the current situation of the global COVID-19 pandemic, how many HDMI 2.1 signal sources will arrive in 2020 or even 2021. CES 2020 is equipped with HDMI 2.1 products, but many manufacturers are facing serious delays in production and shipping plans. Nevertheless, there are already products that can be prepared for the future. All of LG's 2020 OLED TVs have HDMI 2.1 ports. Sony's two top LCD TVs and Samsung's flagship 85-inch Q950TS 8K QLED TVs also have HDMI 2.1 ports. Yamaha stated that its 2020 receiver product lineup will support HDMI 2.1 and will provide services in time for this holiday season to handle the sound of your new Playstation 5 and Xbox X series games. (Again, check the feature list of each product to make sure it supports the features you care about!)

Do you plan to upgrade the system to support HDMI 2.1? What is the feature you are most interested in? Share your thoughts in the relevant forum topics below.

Many thanks to Phil Jones of Sound United for providing HDMI 2.1 education in our YouTube interview series.

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Jacob is a music lover and audiophile who likes to persuade his friends to buy audio equipment that they can't afford. He is also a freelance writer and editor in Los Angeles.

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