Xiaomi Mi 4 Review: Call Quality
Author:Soomal
Source:eng.soomal.com

Rate:05.50/11

The progress of the shape design, the material, the difficulty and precision of processing from the ¡°no design is the best design¡± MI1 to MI4 is obvious, no matter how many criticisms emerge online since it has been released. Soomal was one of the thirty medias who get the test prototypes at first time. All kinds of product reviews appear just the day after the conference, so we cannot race in speed, we just follow our own tempo. Of course the performance of MI4 is concerned by some who just want to make an excuse to buy, but also some others who just want to see it as a joke. Now let us review on call quality of MI4.

According to our reviews, MI3(TD-SCDMA version), RedMI and RedMI Note has been tested completely on call quality, those MI devices performed better in comparison with other devices in similar price, except the low ringtone volume of RedMI. On the contrary, we can obviously feel the terrible call quality of MI2S, but it has no bad effect on its market position because many contemporary phones also worked so bad that at least MI2S is much better than One X. MI4 is equipped with Qualcomm Snapdragon 801, most products with the same SoC perform well in call quality. It¡¯s unlikely to screw it up with this hardware solution and software driver designed by the upstream manufacturers unless tragedy of Sony Z2 happens again.

Earpiece Speaker Test

Conventionally, we place this cellphone indoor with normal signal, and set the call voice volume to maximum, then call 10010, which is China Unicom customer service hotline. Finally record and analysis this China Unicom fixed voice signal with professional sound card and microphone.

Testing Item Mi 4 RedMi Note Mi 3 RedMi
Output Level of Earpiece, dB -11.38 -14.36 -11.4 -11.34

The earpiece speaker volume and timbre of MI4 is almost the same with MI3.

Speaker Test

We place this phone indoors with ambient noise level at 40db or less, and turn up the ringtone volume to maximum, then use a sound level meter to measure sound level at the distance of one meter from the phone.

Testing Item Mi 4 RedMi Note Mi 3 RedMi Mi 2S
Face Up, dB 73.9 69.3 77.4 69.7 73.1
Face Down, dB 73.5 72.5 77.6 69.9 74.6
Face Up, dB 67.6 67.4 72.9 65.7 72.7

It can¡¯t be better that if the bottom speaker can reach Lumia 1020. However, obviously MI4 is looking ahead for iPhone, the volume of speaker is lower than MI3.

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 playing to simulate ambient noise at 6db SNR. MI4 is configured with dual microphone noise reduction with the second noise sampling mic set conspicuously up over the camera.

There are just two choices in noise reduction mode setting, single or dual, which is more precise than that of Samsung and Sony. In the default dual-mic mode, the microphone voice input of MI4 is lower than standard testing level 3dB, and if the user switches it to the single-mic mode, it goes to -16dB.

Testing Item[Mi 4] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction, dB[Higher is Better] 43.9 42.3 46.2 44.3 45.2
SNR Improvement, dB[Higher is Better] 33.8 28.5 35.2 31.8 45.2
SNRI-to-NPLR difference, dB[-4 to 3] -4.4 -2.5 -5.8 -5.5 -1.0
Testing Item[Mi 4, single mic noise reduction] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction, dB[Higher is Better] 35.1 30.9 38.0 38.7 33.4
SNR Improvement, dB[Higher is Better] 22.0 18.5 24.8 24.0 19.9
SNRI-to-NPLR difference, dB[-4 to 3] -9.3 -6.2 -10.1 -11.0 -8.6
Testing Item[RedMi Note] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction, dB[Higher is Better] 31.6 32.7 36.7 33.9 31.3
SNR Improvement, dB[Higher is Better] 23.5 26.9 27.9 20.4 20.9
SNRI-to-NPLR difference, dB[-4 to 3] -5.0 -2.9 -5.5 -6.3 -2.8
Testing Item[Mi 3] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction, dB[Higher is Better] 27.7 28.2 26.2 24.7 33.8
SNR Improvement, dB[Higher is Better] 18.4 22.8 18.9 18.4 24.9
SNRI-to-NPLR difference, dB[-4 to 3] -3.3 -1.2 -4.4 -3.8 -0.6
  • 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 website or official technical data cannot be used for comparison.
MI4 performs well in noise reduction, it would degrade the voice signal in very noisy condition, with the ambient noise well suppressed and filtered. There is no doubt that MI4 is the best one of MI series in call quality with the dual-mic mode on, otherwise the other end would hear nothing. But the ring tone volume is disappointing.
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