In February of this year, the HDMI Licensing Administrator (HDMI LA) released the latest version of the HDMI standard, "HDMI2.1a."New in 2.1a are optional features called "SBTM (Source-Based Tone Mapping)" and "Cable Power".[See another image related to this article] Simply put, SBTM is "the source device such as a game console adjusts the image according to the display performance", and Cable Power is "HDMI without external power supply from USB It is a function that enables long cable transmission.Users who enjoy the latest games on large TVs and gaming displays, and users of 4K/8K projectors that transmit long lengths in home theaters will be interested in this function.Normally, when a new version of HDMI is released, related organizations often hold briefing sessions for the media, but this time there was no briefing session or release in Japanese, and 2.1a information is scarce.Therefore, we interviewed two companies, Panasonic, which has played a central role in formulating the specifications since the establishment of the HDMI standard, and Aim Electronics, a cable manufacturer that has exhibited the latest standard cables at CES and other events, to learn more about 2.1a. I decided to ask.This time, as the Panasonic version, we will introduce the overview of 2.1a and 2.1, focusing on SBTM, by Mr. Toshiro Nishio, who belongs to the Business Development Center of Panasonic Corporation, and Mr. Sanada, who is in charge of TV product planning for the domestic market at Panasonic Entertainment & Communication Co., Ltd. I asked Mr.■ HDMI 2.1a is a “revised version” of HDMI 2.1 specifications.HDMI is an abbreviation for High-Definition Multimedia Interface, and is a standard for digital transmission of video and audio signals.Until HDMI was made, it was necessary to connect analog video cables such as yellow composite, S terminal, D terminal, YCbCr component color difference, and red and white analog or coaxial/optical digital audio cables separately. With the spread of HDMI in various devices, anyone can easily transmit video and sound digitally with a single cable.The founding members of HDMI are Panasonic, Sony, Lattice Semiconductor (formerly Silicon Image), Toshiba, Maxell (formerly Hitachi), Philips, and Technicolor (formerly Thomson).In December 2002, "HDMI 1.0", which supports uncompressed transmission of "1080p video signal" and "192kHz/24bit 8ch linear PCM audio signal" was established, and DVD audio (HDMI 1.1), SACD (1.2), DeepColor / Dolby TrueHD / DTS-HD (1.3), 3D / 4K30p / ARC (1.4), 4K60p / HDR (2.0) and other signals are supported one after another.It has continued to be upgraded and enhanced.In November 2017, we released HDMI 2.1, which realized large capacity and high-speed transmission of up to 48 Gbps by changing the transmission method.In addition to 8K60p uncompressed transmission and 8K/10K120p compressed transmission, it has made significant progress by supporting functions such as dynamic HDR format, variable refresh rate (VRR), and extended ARC (eARC).2.1a released in February this year is positioned as a "revised version" that reflects the addition of "SBTM" and "Cable Power" functions and some revisions to the specifications based on 2.1 formulated in 2017. It's becomingIn addition, even if the HDMI version of the connected device is upside down, it is designed to downgrade to a signal that both sides support and exchange it, ensuring a minimum level of compatibility.Therefore, the user does not need the versions of the devices to be connected.What you have to be careful about is that even if there are products claiming to be "HDMI 2.0 compatible" or "HDMI 2.1 compatible", those products include all the functions added in 2.0 and 2.1. No, 2.1 doesn't support all the features of older versions (eg 1.4).HDMI stipulates a "primary (mandatory)" signal that must be supported.For video, 720/60p and 1080/60i are applicable, and for audio, linear PCM is applicable, but on the contrary, signals other than this are treated as "options", and whether or not they are supported is HDMI. (Neither the familiar 1080/60p nor 1080/24p are actually primary).Basically, all functions extended after HDMI 1.1 are optional.So when choosing a product, it's important to check which features or signals of HDMI it supports, rather than relying solely on the HDMI version number.■ It is SBTM that "tone map" is performed on the source side, not on the display. A person who is in a position to attend and negotiate on behalf of the company when formulating relevant standards.Participated in HDMI as one of the engineers before the establishment of the standard in 2002.He has been involved in HDMI for more than 20 years, including CEC (VIERA Link), which Panasonic put into practical use ahead of the industry, and the idea of ​​separate output that improves audio performance by transmitting audio separately.First, I asked about the difference between HDMI 2.1 and 2.1a.Mr. Nishio (honorifics omitted below): The big difference is the presence or absence of a function called "SBTM".2.1a added SBTM as an optional feature.As for the differences other than SBTM, 4 amendments (minor changes in specifications) and 3 errata (wrong descriptions in specifications) that have been corrected since November 2017 when 2.1 was released have been consolidated into 2.1a. increase."Cable Power", which enables long HDMI cable transmission without power supply from the USB terminal, is one of the four amendments, announced to HDMI adapters (members) in 2019. Thing.Then, for what purpose and intention was SBTM standardized?Nishio: Before talking about SBTM (source-based tone mapping), let me first talk about what a "tone map" is.In general, compared to the cameras and monitors used by video producers, home TVs have different capabilities, so there is a limit to how well the original color gamut and brightness can be displayed.Then, if we talk about how the TV reproduces the image under these restrictions, the TV adjusts the signal to match the color gamut and brightness that the TV itself can express.This is what we call a tonemap.Our VIERA also incorporates this tone map processing. For example, even when an HDR signal with brightness higher than the TV's performance is input, it maintains a smooth gradation without crushing the high brightness areas. Reproduce the image that the creator wanted to show.How to optimize the signal and display it beautifully is also part of the skill of each TV manufacturer.Nishio: On the other hand, some products, such as cheap PC displays, have inappropriate tone map algorithms.Then, even with the same HDR signal, the displayed image will be very different between a PC display and a TV with tone map processing.In the case of games, this difference is noticeable, and if it is a high-brightness explosion effect, the TV can reproduce the shadow of the flame, but the PC display is pure white and nothing can be seen.We often hear about racing games.If the tone map is done properly, you can see the curve at the end of the tunnel, but with some products, the end of the tunnel is pure white and you can't see the course.This will affect the outcome of the game.Unlike content such as TV programs and movies, games generate CG images in real time according to the player's operations.Then, you can create extreme situations that are impossible in normal content, such as repeating the same action to generate a large number of high-brightness effects, or using light and dark differences as viewpoints and compositions.However, under any circumstances, game creators will be in trouble if they cannot reproduce the visuals that should be visible on the display.Based on this, there were voices, mainly from game-related manufacturers, that "I want to tone map on the source device side", and as a result of discussions on the forum, it was included as a new function in 2.1a.In other words, SBTM means that the tone map processing that was previously performed on the TV side is processed and transmitted in advance on the source side that sends the signal.In the world of audiovisuals, it's common to take the stance that "the source device basically does nothing" and "the player is faithful to the original", but for games that generate signals according to the player's operations, it's quicker to make adjustments on the source side. That's what I'm talking about.Nishio: To operate SBTM, you need a combination of a display with SBTM mode and a source device that supports SBTM.As a flow, first, the display passes its own "information" to the source side through EDID (Extended Display Identification Data).The source side then optimizes and outputs the signal based on the information received from the display.As a result, the display will be able to provide users with HDR game images and other images at a constant quality without tone map processing.Unlike televisions, most PC displays have simplified image quality processing.If the source device, such as a game machine or video board, performs tone map processing according to the display performance, a certain level of quality can be guaranteed even with an inexpensive display.In the case of games, in addition to the game video, multiple HDR and SDR signals, such as the player's camera video and chat window, may be mixed in the same screen, so tone mapping on the source side will improve the balance of the overall image. seems easy to take.As of July, no SBTM-compatible source devices or displays have been announced.However, when SBTM compatible devices appear in the future, even if the display side does not have high-precision tone map performance, if compatible devices are combined, it will be possible to enjoy an environment where HDR images can be enjoyed with appropriate quality.However, this SBTM.Inside the forum, opinions were divided between “promoters” and “cautious ones.”The reason for this is that the aforementioned blown-out highlights in game images are a phenomenon that occurs on PC displays, etc., and the reality is that they have little to do with the products of major TV manufacturers.As Mr. Nishio said, the tone map has become one of the "shows of skill" for TV manufacturers, and it is also a point of differentiation from other displays in terms of images.To be honest, there must be something complicated on the TV manufacturer side that the situation where companies A, B, and C produce video of the same quality depending on the control on the source side, Since we know the best, it is best to perform tone mapping on the final display device."Then, will VIERA support SBTM for which the standard has been established in the future?The HDMI site says that SBTM can be supported with a firmware update, but... Sanada: VIERA TVs have been developed with a focus on how to reproduce beautiful and faithful images.In the process, we developed a unique function such as "hybrid tone mapping" that dynamically changes the HDR tone mapping process according to the scene to render vivid images even in high brightness. It is installed in the new VIERA products that will be released this summer.In terms of gaming functions, full resolution display at 4K120p input, ALLM, VRR, AMD FreeSync Premium, dedicated game UI, low latency on some models. We have prepared a constant speed drive mode, and we have prepared specifications that allow you to enjoy games on a large screen and high image quality. There are no plans, but we would like to carefully consider what we will do in the future while paying close attention to the reactions of the game market, creators, and users. Several patterns are prepared for the "information" to be passed to the , and if you only pass superficial information such as the maximum brightness, you can support SBTM by simply rewriting the EDID. Considering the utility of SBTM, it seems likely that SBTM-compatible machines will be released first from PC displays, etc. ■ TMDS is better than FRL, and ARC is better than eARC?! In addition to the new features of HDMI2.1a, we also asked questions about HDMI2.1.In HDMI2.1/2.1a, the conventional TMDS (Transition Minimized Differential Signaling) method is replaced by FRL (Fixed Rate Link). (It is also possible to transmit in TMDS mode depending on the connection partner).Specifically, up to HDMI 2.0, R video (pins 1/2/3), G video (pins 4/5/6), B video (pins 7/8/9), clock (10/ 11/12 pins) were transmitted as differential signals, and audio and control signals were transmitted in packets using the "gap" of the video data.On the other hand, from 2.1, by adopting a method that embeds the clock and transmits it, it is now possible to use the conventional clock lane as a data lane and use all 4 lanes for data transmission.Has the method of sending audio data changed since becoming FRL?Nishio: Conventional TMDS digitized analog signals as they were, and had so-called retrace intervals called H blanks and V blanks.In the case of TMDS, audio is embedded in packets in this blanking and transmitted.On the other hand, in FRL, the blanking period is not transmitted as data, and the audio data is embedded between the active video data.Therefore, the coding method differs between TMDS and FRL.Therefore, although there are differences such as how many bytes of audio should be sent in one packet, the basic method of "embedding audio between images" will not change after 2.1.――Some AV equipment distributes and transmits video and audio as a way to transmit HDMI audio with high quality.It is called "separate output", but when HDMI 2.1 recorders and players come out in the future, separate transmission such as HDMI 2.1 (FRL transmission) for video and HDMI 2.0 (TMDS transmission) for audio is it possible?Nishio: Due to HDMI's characteristic of ``embedding audio between images,'' video signals are still flowing through the audio-only port even when using separate output.For example, in the case of our DIGA, audio data is embedded in the blanking part of the 1080p/60Hz black signal, which is transmitted to the audio system such as the sound bar and AV amplifier.The reason why I chose 1080p/60Hz is that the wider the blanking and the lower the video clock, the less the impact on audio clock jitter performance.If I go down to VGA, the blanking is too narrow and limits how much audio I can send, so I set the resolution to 1080p.To be precise, the rule of audio output terminals is not standardized in HDMI, and DIGA has an image of separately preparing an "AV port that only outputs 1080p" and using it for audio output.By the way, the video port at the time of separate output can be set to the signal of video only by menu setting.Nishio: Looking at the HDMI 2.1 source devices currently on the market, there are no products with dedicated audio output, but it is possible to output video and audio separately as before.There is no rule that you have to match one transmission method, so you can transmit video by FRL and audio by TMDS.This may require verification, but I think that TMDS is more advantageous than FRL in terms of audio quality.This is because, in the case of TMDS, the source and sink were locked on the clock lane, but in FRL, the source and sink clock crystals are separate.If nothing is done, the clocks will gradually deviate from each other, so by adjusting the clocks on the sink side at regular intervals, we prevent the clocks from deviating too much.However, this means that the clock on the sync side is jittering, and as a result, in principle, it will adversely affect the jitter of the audio clock.――There are functions called "ARC" and "eARC" that use pins 14/17/19 to transmit audio signals in the opposite direction from the display to the source device. Is it correct that it contains data? Nishio: Video signals do not flow on pins 14/17/19.However, the specifications require a forward video signal.If it supports the standardized audio format (32/44.1/48kHz, 16bit, etc.) and the ARC/eARC protocol, it can claim to be ARC/eARC compatible.The manufacturer can arbitrarily set what video format to send during ARC/eARC transmission.*Created by the editorial department based on interview materials --In recent years, the number of sound bars and audio amplifiers equipped with dedicated ARC/eARC ports has increased.For example, is it technically possible to use the ARC/eARC dedicated port instead of the separate audio output terminal?Nishio: I think there are such ideas.However, if DIGA has an ARC/eARC output dedicated port, it will have to have an "HDMI input terminal".If an input terminal is provided, a separate input circuit and processing are required.Also, it is not possible to record video via HDMI to the HDD, so I can't think of any advantage of having an HDMI input terminal just for ARC/eARC.In the case of a TV, if a port dedicated to ARC/eARC input is provided, it will be equipped with an "HDMI output terminal".Considering the cost-effectiveness, I don't think it's realistic to have an HDMI input terminal on the recorder and an HDMI output terminal on the TV.――There was an explanation on the HDMI LA site that "manufacturers can manufacture products that support both ARC and eARC. However, backward compatibility with ARC is not defined for eARC."Many users think that ARC and eARC are related, but are they really not backward compatible?Nishio: Although ARC and eARC have similar names, they are not compatible because they use different protocols.Therefore, it does not necessarily mean that "compatible with eARC = compatible with ARC".Sanada: In reality, most eARC-compatible TVs on the market today also support ARC.Nishio: eARC sends audio data differentially, but the data communication channel uses a "common mode" that changes the signal in the same phase, and communication is constantly taking place between the source and sink.However, when communicating in common mode, it inevitably leaks into the differential signal and causes interference in the cable, which in principle adversely affects audio quality.On the other hand, ARC uses CEC for data communication, so such degradation does not occur.eARC supports transmission of uncompressed audio at 192kHz/24bit and up to 32ch. For core users who seek audio quality, there may be cases where "ARC has better quality than eARC".Copyright © 2022 Impress Corporation, An impress Group Company. All rights reserved.