Redmi K40 Series Review: What’s The Difference?

Over the past three years, Redmi has gradually improved its product line, from entry-level to mid-to-high-end, and then to the flagship full line, especially the K series, with remarkable results. It has always been a super cost-effective killer in the flagship camp. We can see this from the sales of the K30 series exceeding 11 million. Moreover, some models have been sold out instantly.

This year’s Redmi K40 series strategy has undergone considerable changes. We mean the company launched three models in this series but one comes with a Snapdragon 870 chip and two sport a Snapdragon 888 chip. Thus, we are dealing flagship models.

Simply put, it is different from the previous positioning of the mid-range standard version and the flagship Pro version. As said, they come with Snapdragon 8 series chips; they all sport the same top-end screen as the Mi 11.

The fundamentals that distinguish K40, K40 Pro, and K40 Pro+ from each other are only the difference between the processor platform models of Snapdragon 870 and Snapdragon 888 and the main camera.

So what is the specific gap between the Snapdragon 870 and Snapdragon 888? What are the differences in the imaging experience of different models of the main camera? Let’s dig deeper with the help of the Redmi K40.

Redmi K40 Design

The three models of the Redmi K40 series have the same appearance. They all use a 6.67-inch punch-hole full-screen with a resolution of 2400*1080, which is what we often call 1080P resolution, and the refresh rate is increased to 120Hz. The screen panel uses E4 luminescent material, 1300nit peak brightness, and supports 360Hz touch sampling rate.

The straight screen protects it from the annoyance of edge picture distortion.

The hole diameter is maintained within the height of the notification bar, only 2.76mm, which is almost the smallest screen hole currently.

At present, 5G smartphones are generally thick and heavy, and the K40 series has optimized and restructured the internal structure of the fuselage, controlling the weight of the whole machine to 196g. The thickness of the fuselage is as thin as 7.8mm.

Prior to this, the side-mounted capacitive fingerprint module was usually designed in a groove, which would damage the visual perception. What is quite unexpected this time is that the Redmi K40 series truly integrates the side capacitive fingerprint module with the power button, and there is even no difference in color, and the integration is stronger.

The back of the fuselage does not use a flat surface. It adopts a continuous curvature G3 curve design. The streamlined micro-arc middle frame transition is more natural. Compared with the previous tough and straight male works, it is much softer and gentler.

The Redmi K series’ rear-camera shapes are consistent and highly recognizable, especially the silhouettes of the previous ‘coin-operated machines’ are quite distinctive. This work has a tendency to unify the design style of Xiaomi and Redmi families. The camera part adopts a racetrack-shaped design. The main camera and the telephoto macro lens are arranged on both sides. The ultra-wide-angle lens and the microphone are in the middle. The curvature of the peripheral camera cover is consistent with the racetrack-shaped curvature.

There are 6 symmetrical openings on the top of the fuselage, which sum up the upper speaker and infrared remote control as a whole.

Obviously, the Redmi K40 series uses stereo dual speakers.

The charging head is still included in the box.

Snapdragon 870 vs Snapdragon 888

The Redmi K40 is equipped with the Snapdragon 870, and the Redmi K40 Pro and Redmi K40 Pro+ come with the Snapdragon 888. Behind this combination is the new and old collocation of Qualcomm’s flagship core.

Snapdragon 870 takes over the misplaced competition

Remember that the Snapdragon 7 Series, Snapdragon 6 Series and other sub-flagship and high-end product lines have encountered dislocation competition impact from the MediaTek Dimensity family and Samsung Orion platform around 2020. Under pressure from rivals, Qualcomm chose to package the highly acclaimed flagship platform Snapdragon 865 overclocking processing into an 870 to take the battle again.

The Snapdragon 870 on the Redmi K40 is the second iteration of the Snapdragon 865. The overall specifications are basically the same as those of the Snapdragon 865 Plus after the initial iteration of the Snapdragon 865. The main change is the use of an enhanced Kryo 585 CPU core. It has a 100MHz improved frequency of 360MHz, which is way higher than that of the Snapdragon 865. So in some sense, we can call it the ultimate overclocking version of the Snapdragon 865.

In other aspects, the Snapdragon 870 is still manufactured in a 7nm process, integrating a large core + three middle cores + four small core CPUs, Adreno 650 GPU, FastConnect 6800 wireless subsystem, Spectra 480 ISP, Hexagon 698 DSP, and an external Snapdragon X55 5G baseband. The latter supports the 5G Sub-6GHz and millimeter wave frequency bands that are truly facing the global market, with a maximum download rate of 7.5Gbps and a maximum upload rate of 3Gbps.

It is worth noting that although some opinions regard the Snapdragon 870 as a ‘Snapdragon 865++’, this is not accurate. The Snapdragon 870 is more like an ultimate optimization and upgrade of the Snapdragon 865, rather than an enhancement on the basis of the Snapdragon 865+. The most typical is that the wireless module of the Snapdragon 870 is not the FastConnect 6900 on the Snapdragon 865+, but the FastConnect 6800. The latter is the native solution of the Snapdragon 865. The biggest difference between the two is whether it supports W-Fi 6E or not.

This also makes Redmi K40 lose support for W-Fi 6E from the hardware level. However, Wi-Fi 6E is an enhanced version of Wi-Fi 6. The biggest improvement is the introduction of support for the 6GHz frequency band, 59 more continuous channels, and the peak speed in short-distance scenarios is much faster. Of course, Wi-Fi 6E still needs the cooperation of terminals and routers to play its full strength.

Snapdragon 888 is the main flagship chip of the series

The specifications of the Snapdragon 888 must be very familiar to everyone. It is manufactured using a brand-new Samsung 5nm process, and it has eight cores in the CPU. But it has upgraded a new architecture layout, especially the world’s first super core of ARM Cortex-X1.

The main frequency of the X1 core of the Snapdragon 888 is the traditional 2.84GHz, and there are three performance-level cores of the A78 architecture, all at 2.40GHz, and four energy efficiency cores of the A55 architecture, all at 1.80GHz. It also integrates Adreno 660 GPU. Qualcomm claims a 35% increase in graphics rendering performance and a 20% increase in energy efficiency. At the same time, the display technology is greatly enhanced to support 144Hz high refresh rate/high frame rate, true 10-bit HDR, and so on.

There have been some controversies surrounding the Samsung 5nm process adopted by the Snapdragon 888 before, and we have a detailed interpretation of this:

There has never been a fixed industry standard for the semiconductor manufacturing process. How to design and name it is entirely up to each individual. Since TSMC’s 16nm and Samsung’s 14nm have been completely messed up, the two companies often start various brainstorming operations in order to look better on the indicators. For example, when TSMC’s 16nm was improved, it was called 12nm, which was more advanced than Samsung’s 14nm.

The process of different wafer factories is indeed difficult to compare from the micro level. For example, the Samsung process technology used by Snapdragon 888 is different from the well-known TSMC process technology. This is especially obvious after 10nm. For example, Samsung chose EUV (extreme ultraviolet light) lithography for certain layers at the 7nm node, while TSMC’s first two generations of 7nm processes used immersion lithography with a wavelength of 193nm.

Although their names are ‘7nm process’, the appearances are always very different. Moreover, Samsung’s subsequent 6nm and the 5nm chosen by Snapdragon 888 are actually the same-generation evolution of the 7LPP process, while TSMC is not. Therefore, the technical path and iteration method of the two have long-term differences. It is currently impossible to judge from the micro level. Samsung’s 5nm and TSMC’s 5nm are better, and there is no difference.

In short, due to differences in different standards, different iteration rhythms, and different naming rules in the process of different wafer manufacturers, it is difficult to compare the high and low performance of the process of different wafer manufacturers at the micro level.

CPU performance test: Ultimate overclocking A77 vs. 2.84GHz X1

First, as for the Snapdragon 870, the CPU part has a 1+3+4 architecture with frequencies of 3.2GHz, 2.42Ghz, and 1.80GHz. The 1+3 large core uses the Coterx-A77 architecture, the L3 cache is 4MB, and the 4 small cores use Cortex-A55 architecture at 1.8GHz frequency.

The CPU of Snapdragon 888 also uses a 1+3+4 octa-core design, upgraded with a new architecture layout, especially the first ARM’s first super large core architecture Cortex-X1, which claims to be 20% higher in theoretical performance than A78. The main frequency of the X1 core is the traditional 2.84GHz, with 1MB secondary cache.

At the same time, the Snapdragon 888 also has three performance-level cores with A78 architecture, both clocked at 2.40GHz, each with 512KB L2 cache, and four A55 architecture energy-efficient cores, both clocked at 1.80GHz, each with 128KB L2 cache. These cores share 4MB L3 cache, 3MB system cache, and the total cache capacity of the entire chip reaches 8MB.

In this comparison, in the CPU part, theoretically the most improved Snapdragon 888 compared to the Snapdragon 870 is the Cortex-X1 super core, which is stronger than the A78, followed by the full upgrade of the three A77 cores to the A78. As for The four small cores, they are still completely unchanged A55.

According to the measured results, the Snapdragon 870 on the Redmi K40 can reach single-core 1003 and multi-core 3350, and the Redmi K40 Pro on the Snapdragon 888 can reach single-core 1135 and multi-core 3701.

Although the Snapdragon 870 has narrowed the gap with the Snapdragon 888 by virtue of its 3.2GHz extreme overclocking, the single-core test results of the Snapdragon 888 are still improved by about 13% compared to the Snapdragon 870, and the multi-core test results have an increase of about 10% , the gain of the X1 super-large core is still quite large.

GPU performance test: Adreno650@670MHz vs. Adreno660@840MHz

In terms of GPU, let’s talk about the Snapdragon 870 first. The frequency of its Adreno 650 GPU graphics core is exactly the same as that of the Snapdragon 865 Plus. Both are improved on the basis of the Snapdragon 865 587MHz, that is, Adreno 650 GPU@670MHz, compared to the Snapdragon 865, its graphics rendering speed is about 10% faster.

Compared with the Adreno650@587MHz of the Snapdragon 865 and Adreno650@670MHz of the Snapdragon 870, the Snapdragon 888 has been upgraded to Adreno660@840MHz in one go. Qualcomm once claimed that the graphics rendering performance has increased by 35%, which may be mainly due to the 43% overclocking.

According to the measured results of GFXbench, Adreno660@840MHz has achieved remarkable results.

The Snapdragon 888 on the Redmi K40 Pro maintained the lead in all test sub-items. Among them, the high-load scenes such as the Aztec ruins Vulcan 1080p/conventional off-screen were the most aggressive, with a gap of 36%. The improvement of other test items is at least about 20%.

It seems that the Snapdragon 888, with Adreno660’s overclocking up to 840MHz, does have a large gain in graphics capabilities and a higher limit on performance. At the same time, the Snapdragon 870 carried by the Redmi K40 is not too far behind, and is in the first echelon of the Android camp with the former.

CPU energy consumption and energy efficiency test: Snapdragon 870 and Snapdragon 888 have the same goal

We use PrefDog and Geekbench to collect the CPU power consumption data of the smartphone and calculate the CPU energy efficiency ratio. The specific method is as follows: The settings of the Redmi K40 and Redmi K40 Pro participating in the test are unified to the lowest brightness, the flight mode is turned on, and the same version of Geekbench is used.

First, we used Prefdog to test power consumption: turn off all background apps of the phone, set at the lowest brightness, and only turn on WiFi. The specific method is to select the phone desktop as the test software, and leave the phone to stand without any operation; get a section of power consumption curve and average power consumption value, and record the value.

Then, we used Geekbench to run the scores separately, collected average power consumption data and subtracted the no-load data during the running time to get the power consumption of the smartphone processor. Combined with the test results, the frame rate, power consumption, and energy consumption ratio data calculated from this are finally obtained.

In order to feel the difference between the two more intuitively, our direct test results and energy efficiency ratio calculation results are summarized in the following table for reference.

Single core
Multi-core

We can find that either single-core or multi-core CPU, the Redmi K40 Pro with Snapdragon 888 can provide more robust performance than the Redmi K40 with the Snapdragon 870. Of course, the power consumption will also increase, but energy efficiency ratio performance of the two is not much different (single-core gap 10%, multi-core gap 1%).

Therefore, combined with our previous special test results of Snapdragon 888 VS Snapdragon 865, it can be basically determined that in the extreme test scenario of Geekbench, whether it is Snapdragon 870 or Snapdragon 888, their CPU peak performance is compared with the Snapdragon 865. The increase produced is not linear, and the increase in power consumption will exceed the increase in performance.

GPU energy consumption and energy efficiency test: Snapdragon 870 outperforms

We used PrefDog and GFXbench to collect the GPU power consumption data of the smartphone and calculate the GPU energy efficiency ratio. The specific method is as follows: the settings of the two smartphones participating in the test are unified to the lowest brightness, the flight mode is turned on, and the same version of GFXbench is used.

First, we used Prefdog to test the power consumption. With the lowest brightness, we only turned on WiFi and the necessary tools. The specific method is to select the smartphone desktop as the test software, and leave the phone to stand without any operation. Then we have to get the power consumption curve and average power consumption value, and record the value.

Then, we used GFXBench to perform a single off-screen running score, collect average power consumption data and subtract the no-load data during the running time to get the power consumption of the phone processor. Due to the cumbersome details of the specific test process, we will directly summarize our test results in the following table for reference.

We can see more intuitively that while the Snapdragon 888 provides more powerful GPU performance, the power consumption will also increase. The energy efficiency ratio of each test item will be reduced compared to the Snapdragon 870 equipped with Redmi K40 (approximately a difference of about 20%), the difference in energy efficiency ratio between the two is really not that big.

A series of tests on body temperature, storage, and AnTuTu

Temperature measurement

The test was carried out in an environment with a room temperature of about 21°C.

The highest temperature of the Redmi K40 body was 27.4°C before the running points, and it rose to 34.8°C after the running points.

The highest temperature of the Redmi K40 Pro body was 28.9°C before the run, and rose to 39.5°C after the run.

Redmi K40
Redmi K40 Pro

Storage test

The entire Redmi K40 series is equipped with dual-channel UFS 3.1. According to the actual measurement, compared with the previous UFS2.1, it has achieved higher write performance, which is at the mainstream level, and it is more convenient to handle a large amount of data throughput.

Redmi K40 Pro speed test results are slightly higher than K40

AnTuTu

The Redmi K40’s AnTuTu running score surpassed most of the Snapdragon 865 models, and is basically second only to the Kirin 9000 and Snapdragon 888 models in the Android camp.

Redmi K40 Display: 120Hz + E4 + AMOLED

If you must select the most important ‘three major features’ of current smartphones, we think that you cannot escape the processor platform, screen and camera module. In fact, from the analysis of the components of flagship smartphones such as iPhone and Samsung by some analysis institutions, it is found that these three items account for the bulk of the BOM material cost.

Redmi K40

All K40 series use an E4 AMOLED screen, with a size of 6.67-inch.

Accuracy, color performance, etc. have reached the top level. Peak brightness is 1300nit, contrast, 00,000:1, JNCD=0.36, △E=0.35. It is worth mentioning that Redmi K40 Pro received the highest rating of A+ in the test conducted by the authoritative screen testing agency DisplayMate.

The K40 series screen has a refresh rate of 120Hz, which means that more pictures can be displayed at the same time, bringing smoother picture performance in scenes such as video playback, system operation, and games. At the same time, the K40 industry first released a 360Hz three-finger touch, which is even higher than some well-known gaming smartphones.

However, the quality of a smartphone screen is not only determined by the above-mentioned parameters. When watching the screen, we often experience eye fatigue because the color temperature of the ambient light does not match the color temperature of the screen.

The Redmi K40 series supports 360° front and rear dual light perception. Through the integrated judgment of the front and rear light sources of the fuselage through the front and rear light sensors, the recognition accuracy of ambient light is improved, and it supports 8192 levels of brightness adjustment and automatically performs smooth brightness adjustment.

It is worth mentioning that the K40 series has a built-in dedicated ambient light sensor, which can detect ambient light color information through multiple internal light channels, and compensate the screen color temperature according to different ambient light, making the display color temperature more in line with the ambient color temperature and more comfortable.

Here we use Mijia desk lamp 1s (2600K-5000K color temperature adjustment) to adjust the color temperature of the ambient light, and test the color temperature adjustment of Redmi K40. As shown below, the effect is quite obvious.

Redmi K40 Camera

The only difference in all three models is the main camera. Other aspects are exactly the same. Simply put, the Redmi K40 uses IMX582, Redmi K40 Pro uses IMX686, Redmi K40 Pro+ uses Samsung HM2, and all three are equipped with the same 8MP super wide-angle sub-camera and classic 5MP telephoto macro sub-camera.

Among them, the IMX582 on the Redmi K40 is actually not much different from the IMX586. The main specifications of the two are the same: both are 1/2″ type sensors, support 48MP through Remosaic hardware, and also support four-in-one 1.6μm large pixels.

The main difference is that the IMX582 supports 4K resolution at 30 frames video recording, while the IMX586 supports 4K resolution at 60 frames. Except for video recording, there is not much difference between the two. So it can be regarded as a fine-tuned version of IMX586.

We have seen the IMX686 on the Redmi K30. It can directly display a 64MP screen with 9248×6944 pixels by hardware, and has a four-in-one 1.6-micron large pixel unit, and it is a 1/1.7-inch large photosensitive element. With outsole + high pixels, F1.89 aperture, 6P lens, it is an upgraded variant of Sony IMX586.

In other words, from the paper parameters alone, the main camera of the Redmi K40 Pro is indeed slightly stronger than that of the K40.

Daytime Samples

Main camera macro
Main camera macro
2X (main camera cropping)
2X (main camera cropping)

Let’s first look at a set of 1X to 2X sample comparisons. The Redmi K40 and K40 Pro have different color adjustment tendencies, and the difference in specific imaging details is almost imperceptible.

Ultra wide angle
Ultra wide angle

Due to the use of the same specifications of the super wide-angle sub-camera, the super wide-angle image performance of the two is equivalent.

Main photo
Main photo

In the case of relatively sufficient light, the main camera of the Redmi K40 Pro has relatively obvious advantages in imaging details due to larger pixels. In addition, there is a more intuitive difference between the two in terms of imaging color adjustment.

Night samples

With relatively sufficient artificial light sources, it is difficult to observe the gap between the Redmi K40 and the K40 Pro.

Regular mode
Regular mode
Night scene mode
Night scene mode

In a low light environment with relatively lack of artificial light sources, the difference between the Redmi K40 and the K40 Pro will be more obvious. The most intuitive point is that the latter’s picture is relatively pure, and the samples can still remain relatively high when the night mode is not turned on. With some brightness, the HDR effect in night scene mode is more natural and softer than that of the Redmi K40.

On the whole, the image performance of the Redmi K40 and the K40 Pro are basically similar. If you don’t delve into the purity of the main camera in low-light environments, you don’t have a preference for one of the color palettes, and you don’t care about the 4K 60 that is missing in the main camera of Redmi K40.

Charging endurance test: It may be the fastest 33W fast charge at present

The Redmi K40 series comes with a 4520mAh battery as standard.

We played an online video, putting the volume on silent and brightness on 75%. According to the monitored current information, it can be estimated that the online video battery life of the Redmi K40 under test conditions can reach about 12 hours.

Under the same test conditions, based on the monitored current information, it can be estimated that the online video battery life of the Redmi K40 Pro under the test conditions can reach about 8.2 hours.

All Redmi K40 series come with a 33W charger. It takes 50 minutes to charge from 3% to 100%. It may be the fastest charging model we have seen so far with a charging power of about 30W.

Conclusion

As you can see, this is a true dual-flagship approach. The Redmi K40 series smartphones don’t differ much. Of course, there are some differences such as the processors, the main camera lenses, but the rest is almost identical. So if you don’t care of such minor differences, even the Redmi K40 with a 1999 yuan price tag can be an ideal choice.  

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