vivo X21 UD Review: Audio
Author:Soomal
Source:eng.soomal.com

Rate:10.00/50

Xplay undertaken the title of best sound among smartphones, while X series just provide sound above than average since X6. Therefore, the X21's sound quality will not be suspicious, better than those without separated DAC, but not as good as the Xplay series.

X21 uses Qualcomm Snapdragon 660 AIE SoC wih built-in audio I/O controller, which provides the most basic sound quality assurance from the years of testing. The X21 continues the separated DAC design of the audio subsystem, but not a flagship type. It adopts AKM AK4376, which is the same as X20 ordinary version. The SNR of the DAC is as high as 130dB, but the actual performance is not so stunning. We have tested several models based on the AK4376, and they are not better than the ES9018 based ones. The performance is good, but the difference in sound is obvious.

X21 began to build "deep space sound effects", which are said to be self-developed. Nothing special, just simulates the everberation effects of several common environments or application scenarios. It also provides directional optimization for vivo headsets, which may come from Dirac.

We start to add USB audio device compatibility test and Bluetooth decode supported test as the popularity of smartphone external device. We choose Musiland MD30 Plus as our audio device, using SuperDSP platform that is compatible with UAC2.0. Another one is Matrix Mini-i Pro 2S, adopting XMOS program. The reason why we choose these two is that they can display the current sampling rate on screen. We will add more devices in the future.

Testing Smartphone iPhone X iPhone 8 Plus Samsung Galaxy Note 8 Samsung Galaxy S8+ Huawei Mate 10 vivo X20 Plus OnePlus 5T vivo X21
Musiland MD30 Plus Auto Switch Sampling Rate Auto Switch Sampling Rate Locked to 48kHz or 192kHz Cannot Work Properly Locked to 96kHz Locked to 48kHz Locked to 48kHz Locked to 48kHz
MATRIX Mini-i Pro 2S Auto Switch Sampling Rate Auto Switch Sampling Rate Locked to 48kHz or 192kHz Locked to 48kHz or 192kHz Locked to 96kHz Locked to 48kHz Locked to 48kHz Locked to 48kHz
Comment greater than or equal to 96kHz will be locked to 192kHz, others are locked to 48 kHz

Tests have found that the X21 locks the output sample rate to 48 kHz when connected to an external USB device. This means that SRC is generated when other sample rates are input. We have already feedback to vivo on this issue, but there is no improvement in X21, we do not think that vivo solve this problem will have technical barriers, it will not increase the additional hardware costs, Soomal hopes vivo's attention to the needs of external USB audio devices.

X21 support aptX, so, when choosing wireless headphones, aptX supported headphones are preferred

By convention, we use professional sound cards to record sounds, combining with common analysis, to provide quantitative results. The maximum output level of X21 in Hi-Fi Mode is -8dB, while it is -12dB in normal mode.

The test was successful. No SRC occurred in either the Hi-Fi mode or the normal mode. Normal mode does not support playback Hi-Res audios, and Hi-Fi mode passes smoothly.

Testing Item 44.1kHz 44.1kHz [Hi-Fi] 48kHz 48kHz [Hi-Fi] 96kHz [Hi-Fi] X9 44.1kHz [Hi-Fi]
Noise Level, dB -96.5 -96.0 -97.0 -96.8 -110.8 -95.8
Dynamic Range, dB 96.3 96.7 96.3 96.7 110.8 96.4
Total Harmonic Distortion(THD), % 0.0006 0.0013 0.0006 0.0014 0.0013 0.0013
Intermodulation Distortion, % 0.0042 0.0044 0.0041 0.0044 0.0017 0.0044
Stereo Crosstalk, dB -75.1 -75.1 -75.6 -75.1 -81.4 -75.1

The test was successful. No SRC occurred in either the Hi-Fi mode or the normal mode. Normal mode does not support playback Hi-Res audios, and Hi-Fi mode passes smoothly.

In real hearing part, compared with Xplay 6, the best smartphone audio, X21 is worse in sound thickness, density, dynamic, transient, and resolution. If we turn to smartphones without separated DAC, such as iPhone or HTC U11 3.5mm adapter, X21 also does not win in powering. When powering full-sized headphones, it may not be better because the low frequency may be more likely to get out of control. When the earbuds are small, the X21 has certain advantages, in terms of resolving power, layering, and stereo image, it has more exquisite and more tolerant performance, and more in line with the performance of Hi-Fi.

X21 is divided into normal version and under screen fingerprint identification version, the audio subsystem of both are the same, and of course the same sound quality, but they are not the same in bounding earphones. The XE710 is distributed on the X21 UD version, which earphone is similar to the highly acclaimed XE800, which both are a ˇ°bean sproutˇ± design. However, the XE710 is not an active plug and its appearance has changed slightly. The speakers are also different. Sound performance also varies, the XE800's sound is delicate and balanced, and the XE710 clearly appeals to the young people's taste tuning, with a large amount of low frequency, which also loses the resolution and image power of the midrange, and the high frequency performance is far worse than the XE800.These two headphones are not at a same level, the XE800 is already qualified for entry-level enthusiasts. Of course, the XE710 is still better than the previous XE600, and it's sincerer to be bounding earbuds. Even if compared to other competitors, the XE710 is relatively good. However, this headset is still not worthy of the X21's sound quality, you can consider buying an easy-to-drive small earphone to combine with the X21 to avoid weaknesses.

The performance of X21's sound quality is not surprising, for its market locating, better than competitors. Even if it reaches the design goal, vivo can show more sincerity, and users can also enjoy more benefits. The X21's sound quality can meet most of the less demanding and slightly discerning consumer demands.

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