Among the current display interfaces on the market, VGA and DVI have gradually withdrawn from the stage of history, Type-C is still a niche, and DP (DisplayPort) and HDMI have become standard configurations of mainstream products. The current mainstream graphics cards are also based on this Two output interfaces are the main ones, and a new question is born: When these two interfaces are both available, which one is better?
For most ordinary consumers, the display can be connected to the host normally. It doesn’t matter which interface is used. It can be used normally anyway. But for DIY players, this problem is very important, but it depends on the performance of the graphics card and the display. Parameters compared toThis is another problem that is easily overlooked.
Especially in high-end monitors equipped with FreeS, HDR, high resolution (above 4K), high-brush (above 144Hz), etc., there are usually differences between these two interfaces to connect to the same device. If you cannot choose the best connection method, Various compatibility issues may occur, resulting in the inability to play the best performance of the graphics card and monitor.
To know how to make a choice that suits you, we must first re-understand the two interfaces of DP and HDMI.
The history of DP and HDMI
From the perspective of development history, HDMI is regarded as a predecessor. The first standard has been published as early as 2002. The latest standard protocol version is HDMI2.1, and the DP interface is regarded as a latecomer. The first standard appeared in 2006, and the current latest standard The protocol version is DP2.0. These two interfaces are a sign that the video transmission interface has entered the digital age. Although the previous DVI interface also uses digital signals for transmission, it cannot carry audio and data streams.
In the Type-C interface of the Thunderbolt and USB3.* protocols, they also transmit video signals through the DP protocol channel for digital image transmission, which is strictly speaking a special interface form of the DP protocol. Thunderbolt 2 supports DisplayPort 1.2, while Thunderbolt 3 and the full-featured Type-C following the USB3.1 specification support the latest DP3.0 protocol, but there is a difference in bandwidth (Raiden is 40GB/s, USB3.1 is 10GB/s). There are also certain differences when considering only the video transmission capacity. We will have the opportunity to talk about this later.
After years of development, although the basic forms of the DP interface and HDMI interface have hardly changed, there are huge differences in the transmission capabilities of the interfaces of different protocol versions. Therefore, we are considering which of the two is more suitable. The specific version must be considered.
Both DP and HDMI standards are backward compatible. The HDMI1.0 cable you bought in ten years can still be used with the latest RTX30 series graphics cards. However, due to the barrel effect of the connection between the monitor, cable and graphics card, the upper limit of the maximum display capacity can only be the lower one between the two.
This connection may mean that a 4K gaming monitor that supports 144 Hz and HDR with RTX3080 will eventually only run in 4K and 24Hz modes, completely unable to release the true capabilities of the two hardware. This example may be extreme, but it directly reflects the key to choosing HDMI or DP: whether the performance of the hardware can be used perfectly.
The following figure shows the relevant information of the DP interface and HDMI in the past. To avoid the embarrassing situation mentioned above, you can quickly find the supported display modes in this table.
The most important parameters of these two interfaces in each generation of interfaces are transmission rate and data rate. In the early DP and HDMI annotations, digital signals were mostly transmitted using 8b/10b bit rate encoding. In the 8b/10b encoding mode, it means that every 8 bits of data requires 10 bits of transmission bandwidth in actual transmission, and these extra redundancy are used to ensure the integrity of the signal, which means that they only have 80% of the theoretical bandwidth Can be used to transfer data.
Under the latest protocol, DP 2.0 uses 128b/132b for transmission, and the coding efficiency is increased to 97%, while HDMI 2.1 uses 16b/18b for transmission, and the coding efficiency is 88.9%, although HDMI is also equipped with auxiliary channels for transmission Other data, but the impact on the data rate is not significant,In addition, the DP interface of the same generation generally has a higher transmission rate, so the latest generation of DP interface has a higher data rate than HDMI.To understand this, we need to better understand the meaning of transmission bandwidth.
The meaning of data transmission bandwidth
All video data transmitted by digital transmission methods (including DP, HDMI and DVI interfaces) need a certain data band bandwidth, and each pixel on the display has three data points of red, green and blue (RGB) , Or use brightness, blue chromaticity difference and red chromaticity difference (YCbCr / YPbPr) three data points for data transmission.
At the output end, no matter what operations are performed inside the graphics card, the final generated data will be converted into signals for display. These real signals generally contain a 16-bit RGBA information (where A is alpha meaning transparency information).
The most common standard currently uses 24-bit color. In this mode, the red, green, and blue component data of each pixel occupies 8 bits of data respectively. This is also the source of the bit depth data in our computer display data. In HDR and high color depth displays, in order to display richer color data, the data occupancy of each color is increased to 10-bit data, which means that 30-bit color for each pixel can bring a better display effect.
In some top professional monitors, the bit depth has even increased to 12-bit and 16-bit, but it is still very small at present. Most of the products we can contact with ordinary consumers are mainly 8bit, and a small number of high color accuracy and HDR displays are 10bit. In this case, the display signal uses 24-bit or 30-bit data per pixel. We multiply this number by the number of pixels and the screen refresh rate to quickly calculate the minimum bandwidth required to achieve this transmission screen .
Taking the above display as an example, the bandwidth required to achieve a display effect of 3440 * 1440 @ 100 Hz: the bandwidth (data volume per second) required in 8bit mode is 24*3440*1440*100Hz=118886450000bps≈13.8Gbps, The bandwidth required in 10bit mode is 30*3440*1440*100Hz=14860800000bps≈17.3Gbps.
When the cable or the output port interface cannot meet the demand, you can only choose to reduce the resolution, reduce the refresh rate and turn off HDR. When I use a laptop to connect, I use the HDMI2.0 interface (14.4Gbps). The 3440*[email protected] Hz mode can be turned on smoothly when connected, but when the full-featured Type-C (USB3.1 protocol) is used for connection, limited by the interface bandwidth (10Gbps), only 3440*[email protected] display can be turned on mode
Moreover, in actual applications, meeting this minimum theoretical transmission bandwidth is not rigorous enough. In actual applications, a certain amount of redundancy is needed. More complex calculations are needed to determine the required bandwidth. In order to visually reflect the bandwidth requirements, video The Video Electronics Standards Association (VESA) has introduced a set of intuitive reference standards.
Just check this table with the interface specification bandwidth appearing above to quickly confirm the applicable resolution. If the required data bandwidth is less than the maximum data rate supported by the standard, this resolution and frame rate can be used normally.
It should be noted that the standards formulated in the above figure are based on uncompressed signals. In order to output higher resolution pictures under limited hardware bandwidth conditions, the HDMI and DP interfaces have also added display streaming compression technology (Display Stream Compression, referred to as DSC) support, this technology can help the device to better overcome the physical limitations of interface bandwidth. The DP side added support for DSC1.2 as early as version 1.4, and the HDMI side also added support for this technology in the latest 2.1 version.
At 8K and 60Hz, in the basic 8bit mode, a data bandwidth of 49.65 Gbps is required. When the 10-bit HDR mode is turned on, a bandwidth of 62.06 Gbps is required. When the 8K+120 Hz+10bit HDR is turned on, in the uncompressed state Transmission requires up to 127.75 Gbps of transmission bandwidth, which currently has no interface to meet this demand.
And by converting to 4:2:2 or 4:2:0 YCgCo and using incremental PCM encoding, DSC can provide up to 3:1 compression ratio, claiming to provide a “visual lossless” effect, using DSC to make 8K The required bandwidth of +120Hz+HDR is only 42.58 Gbps, which can achieve this extreme display effect under the existing HDMI2.1 and DP2.0 interfaces.
In addition to transmitting video, HDMI and DP also need to reserve bandwidth to transmit digital audio data. Under the current standard, they currently use up to 36.86 Mbps (0.037 Gbps) bandwidth audio for audio. Although it will occupy the overall bandwidth, the overall impact is not Not big.
From the above introduction, it is not difficult to see that the bandwidth calculation method through simple resolution * refresh rate * color depth is obviously not comprehensive enough, because the specific performance needs to consider factors such as timing standards, encoding methods and audio bandwidth.Although the occupied bandwidth is still the larger the better, it is obviously not the only reference standard that affects the transmission capacity of the video signal.
The pros and cons of DP and HDMI interfaces
In the current mainstream market, DP1.4 is the most powerful and common version of the current DisplayPort standard. Although the DP2.0 specification was released in June last year (2019), people still do not support the consumption of this interface. Class graphics cards and monitors were introduced.
The RTX30 series graphics cards launched some time ago are still equipped with the DP1.4 interface. Although the available bandwidth is not as good as the HDMI 2.1 at the same time, the performance of up to [email protected] can already meet current needs.
However, 8K display devices are currently mainly TV-based, and basically use the HDMI 2.1 interface to realize 8K signal transmission, and referring to the past performance of DP in the TV market, it is unlikely that products using DP2.0 will be launched in the short term. , In other words,Before the large-scale science popularization of DP2.0, the extreme transmission performance of DP is temporarily unable to compare with HDMI2.1.
One of the advantages of DP is its native support for variable refresh rate (VRR). This technology has become part of the DP standard after DP1.2a. This is also the basis for the large-scale popularization of FreeSync technology (compatible with G-Sync) in recent years. To use this technology, you must use the DP interface.
In addition, due to the addition of a fixed buckle switch, the stability of the DP interface and the wire is better than that of HDMI, and there is almost no risk of “broken head” if you accidentally pull it like HDMI.
And DP can also connect multiple screens to a single port through multi-stream transmission (MST). Some displays also support the DP serial function based on this technology (displays are directly connected through the DP interface), which will be more extensible.
Since HDMI requires a certified standard protocol, and DP is an open standard protocol,Many innovations in display technology (such as DSC, G-Sync and FreeSync) will appear on DP first and then slowly appear on HDMI.
There is also a key parameter on the DP cable that limits its use scenarios: its maximum length is limited to less than 3m under the current standard. This factor makes it unlikely to be used in home theater, long-distance signal transmission and other application scenarios. In 99% of cases, it can only be used between a desktop host and a monitor, which indirectly limits the application of this interface to devices such as TVs and projectors.
In terms of the most important transmission bandwidth, due to the late-comer advantage of the DP protocol, HDMI has always been slightly inferior to DP in its bandwidth performance during the same period. This time, HDMI2.1 is the first to appear on the market. Although it has been “lagging behind” on paper parameters, in the case of non-extremely high resolution + refresh rate operation, the current most mainstream DP1.4 and HDMI2.0 will actually not have a perceptible difference.
Since the release of HDMI 2.0 in 2013, the HDMI interface has been able to achieve [email protected] Hz transmission effect in the case of 8bit color, and achieve a display effect of up to [email protected] in the 4:2:0 YCbCr output mode, but there will be edges. It looks fuzzy.
As for the lack of variable refresh rate technology, HDMI has also added support for FreeSync and G-Sync technology through AMD’s expansion chip starting from 2.0b, and included this technology in the new standard in the HDMI 2.1 protocol.
So far, only part of Nvidia’s RTX20 series and the latest RTX30 series graphics cards will support the HDMI2.1 interface (some non-public graphics cards are only equipped with the HDMI2.0 interface), and most displays are still equipped with the HDMI2.0 interface.Therefore, considering the comprehensiveness of functions, using a desktop computer to connect to the display is the best way to use DP.
Although it does not have a long-term advantage in theoretical performance, the HDMI specification has extremely high popularity and compatibility. When the standard was first introduced in 2004, millions of HDMI-equipped devices had been shipped, and in 2020 , Devices with HDMI can be seen everywhere, and mainstream real-life devices will be equipped with this interface.
Although the graphics card does not yet have products that support the full specification HDMI2.1 interface, it is the first to sell a large number of HDMI 2.1 devices on consumer devices such as TVs, Blu-ray players, and home theaters. The popularity and versatility will still be more than DP in the short term Strong.
The biggest advantage of HDMI over DP in terms of practicability is the cable length of up to 15m, which is five times that of DP cables. This feature is very important for players who use a desktop computer to connect to a monitor, but for home theaters and other scenarios that require long-distance connection, so that this kind of cable has a richer application scenario.
DP and HDMI: How do gamers choose
We have already introduced the technical parameters of DisplayPort and HDMI. Everyone has a good understanding of these two transmission protocols. So back to the original question, but which connection method is actually more suitable for gamers?
Some of it depends on the hardware you already own or plan to buy. Both of these two standard protocols can provide an excellent gaming experience, but if you want an excellent gaming experience, among the products currently available on the market, HDMI 2.1>DP 1.4>DP 1.3>HDMI 2.0, and the currently released Among the agreements, the theoretical performance of DP 2.0 should be the best, but the prospects for popularization of the agreement are still unclear.
In some high-brush + high-resolution application scenarios, gamers need to choose according to their platform.
For gamers using N cards, the best solution at present is to use the DP 1.4 interface to connect to a G-Sync-equipped monitor.The new HDMI is only useful when connected to a TV, because currently the only G-Sync-compatible monitors through HDMI 2.1 are TVs, and on ordinary monitors, the use of DP can fully utilize the characteristics of the N card.
The A card game player’s choice is relatively loose, because the current display with FreeSync function can be turned on through the HDMI interface.Therefore, when A card is used with DP 1.4 and HDMI 2.0, there is not much difference in function and practicality.However, DP will still be the preferred standard for PC monitors, because many HDMI FreeSync monitors can only operate at lower resolutions or refresh rates, and fewer products above 144Hz.
If you already have a refresh rate below 144hz, does not support G-Sync or FreeSync function, and the display supports both HDMI and DP input, and the graphics card is also equipped with both interfaces, this connection method The choice is not so important.
With 2560 * 1440 (1440P) @144 Hz resolution and 8bit color depth, DP1.2 and HDMI 2.0 and above protocols can work normally. Any connection type below this value will work normally. There is indeed no practical difference between using these two interfaces (theoretical signals that can be transmitted are the same).
In the use scene of desktop computer with monitor, DP interface is obviously the best choice, Can give full play to the performance of the output end, so current graphics cards will be equipped with more DP interfaces. Although the new RTX 30 series graphics cards support HDMI 2.1 interfaces, they generally only have two or less.
In the scene of connecting the host to a large screen such as a TV or a projector, HDMI is still the best choice for a long time because it has a longer transmission distance and wiring is more convenient. The most important thing is that HDMI has Equipment compatibility far beyond the DP interface,At present, devices with screens above 50 inches are rarely equipped with DP interfaces, and HDMI will still be the preferred interface for a long time to come.
In the end, although DP has the advantages of specifications, HDMI’s excellent compatibility and convenience can help it have a richer application scenarios, and the two standards overlap in many fields and technologies.
The VESA organization responsible for the development of the DisplayPort standard mainly considers the application scenarios in the PC field. The HDMI protocol developed by the Consumer Electronics Alliance will definitely give priority to consumer-grade devices such as TVs and projectors. Their different concerns eventually lead to these two The protocol has subdivided different application scenarios.
For high scores, high color gamut and full functional experience, use DP. If you need a large screen and strong compatibility, use HDMI. Fans of game users can choose according to the usage scenario. For more than 90% of ordinary users, it will affect the display effect. The bottleneck may lie in the graphics card and the monitor, so don’t worry too much about the choice between the two.