vivo X21 UD Review: Call Quality


X21 is the first mass-produced mobile phone that supports under-display fingerprint recognition, and adopts a notch screen design. The market price of 6GB of RAM and 64GB of internal storage starts at 2,898 Yuan (about $450). Our prototype is an under-display fingerprint version of the ice black color, priced at 3598 yuan (about $550). X21 is also the representative product of vivo after icc organization joined. The system defaults to the standard P3 wide color gamut display. The built-in photo app uses icc profile to support sRGB color image browsing and processing. So how does this popular handset perform in voice calls?

Vivo X21 processor configuration for the Qualcomm Snapdragon 660AIE [AI enhanced version], hardware features is basically the same as X20s. Because the CPU technology jumps directly from the Snapdragon 653s 28nm to the advanced 14nm process, the peak frequency from 1.8GHz Up to 2.2GHz, the GPU and DSP operating frequencies have also been significantly improved, and heat and power consumption have been lower at high loads. Supporting X12 LTE basebands have improved 4G carrier aggregation and download speeds. The X21 supports wireless transmission protocols such as dual-channel MIMO 802.11ac high-speed wireless LAN and Bluetooth 5.0, which is consistent with the X20. Supports dual SIM dual standby and Micro SD storage expansion. The X21 runs on Funtouch OS, an Android 8.1-based system. The call feature provides incoming call number information and Samsung-styled high volume gain mode. By convention, voice calls are still done through China Mobile 4G and China Unicom's GSM network.

Earpiece Speaker Test

We place this cell phone indoor with normal signal, and set the call voice volume to maximum, then call 10010 [GSM], which is China Unicom customer service hotline. Then use professional sound card and microphone for recording and analysis.

Testing Item vivo X21 R11 Plus OnePlus 5T vivo X20 Plus vivo X20 vivo X9 Plus OPPO R11
Output Level of Earpiece,dB -10.08/-9.4 -10.73 -9.43 -10.2 -10.1 -10.15 -9.51

Due to the narrow width of notch on the top, X21's earpiece speaker opening is narrower than X20, and the output volume and sound style are consistent. The maximum volume is partial dry and rough. Press and hold the volume for the maximum volume during the call. The key will go into high-gain mode, but the final output will have a small increase in volume, perhaps in a noisy environment.

Loud Speaker Test

Speaker test was undertaken indoors with ambient noise level at 40dB or less, we turn up the ringtone volume to its maximum, and then use a sound level meter to measure sound level at the distance of one meter from the phone.

Testing Item vivo X21 R11 Plus OnePlus 5T vivo X20 Plus vivo X20 vivo X9 Plus OPPO R11
Face Up,dB 77.7 79.4 75.7 78.7 78.8 78.1 75.5
Face Down,dB 78.2 78.2 75.9 79.4 80.1 78.2 75.8
In Camera Bag,dB 72.0 74.1 73.0 73.2 72.8 70.0 69.4

The loud ring volume of the X21 is 1dB lower than that of the X20. Although it is loud enough, there is no loud speaker. The quality of the sound is significantly thinner and rougher than that of the S9 and other high-end phones. The tone and sound control power is slightly better than that of the X20.

Noise Reduction Test

We place this phone indoors with ambient noise level at 32db or less, in the middle of the room, we use a human-like structure "handholding" the phone to send voice signal, and put surround speakers in a certain distance playing 5 kinds of simulating ambient noise at 6db SNR. Then we standardize the recording from this end, and run a specific program comparing this recording with raw speech recording and noise-speech mixed recording to get noise reduction level, SNR improvement and SNRI-to-NPLR difference quantitative result.

Testing Item[Hand Holding] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction,dB[Higher is Better] 48.7 48.1 49.1 49.3 37.9
SNR Improvement,dB[Higher is Better] 38.7 41.8 40.0 39.8 27.2
SNRI-to-NPLR difference,dB[-4 to 3] -5.1 -2.9 -5.8 -5.3 -0.4
Testing Item[VoIP] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction,dB[Higher is Better] 42.7 42.2 45.5 44.0 35.7
SNR Improvement,dB[Higher is Better] 19.4 20.2 22.3 20.8 20.1
SNRI-to-NPLR difference,dB[-4 to 3] -3.5 -1.7 -4.9 -4.9 -0.1
Testing Item[GSM Hand-Holding] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction,dB[Higher is Better] 24.7 10.5 37.6 36.8 18.1
SNR Improvement,dB[Higher is Better] 12.2 5.7 25.3 25.0 5.6
SNRI-to-NPLR difference,dB[-4 to 3] -5.2 -0.2 -5.7 -5.5 1.4
  • Total Noise Level Reduction, TNLR: Total Noise Level Reduction illustrates the reduction of ambient noise level. The average level is above 5dB. Theoretically, higher TNLR would be better, but an over high result may be caused by severe attenuation of voice signal, or interruption caused by poor phone signal or noise reduction algorithm flaw.
    Signal-to-Noise Ratio Improvement, SNRI: capability of an NS method to enhance the speech component of a noisy speech signal from an additive background noise. SNR improves after noise reduction by comparing noise-reduced and raw voice signal. Generally, the improvement is over 4dB.
    SNRI-to-NPLR difference, DSN: the signal level difference between raw and noise-reduced. Noise reduction process would attenuate voice signal level, cell phones would gain signal to ensure the call quality. Theoretically, it would be best that signal level remain the same before and after noise reduction. A standard signal level peak is -2.5dB. If the signal was gained too high, overflow would happen, and that means frequent crackle, too low, voice signal strength would not be enough, and that means the sound would be too low, and the other end would not hear clearly.
    The result is just a test reference under similiar circumstances or conditions, third-party websites or official technical data cannot be used for comparison.

The noise reduction effect of the X21 in the hand-held mode is more pronounced than that of the X20. Even relatively difficult music-based background sounds are filtered more cleanly. However, in some persistent high-intensity noise environments, some coherent information such as sound ventilation and nasal sounds of X21 voice information will be partially filtered out. The noise reduction performance of VoIP is somewhat normal, and of course it will not affect normal use. In the hands-free talk mode, the X21 performs better than the X20 under various preset background noises, and there are some places where it is slightly worse. For example, pink noise, fetal noise, and other noise filters are slightly better than the X20, but the voice information is lost. Also relatively high. On the whole, the X21's call, loudness, and sound quality are basically the same as those of the X20. However, the noise reduction algorithm is relatively more aggressive, and the noise can be filtered and processed more cleanly. However, sometimes some voice information is insufficiently consistent and natural. Manufacturers can make some adjustments and optimizations for this.

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