Google Pixel XL Review: Call Quality
Author:Soomal
Source:eng.soomal.com

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Pixel series replaced Nexus series to be the latest Google Android brand since Pixel C released in 2015. The Pixel series are no longer budget phones, they are sold at similar price like Samsung and Apple's flagships. The XL sized Pixel XL is sold from $769. This smartphone is just equipped with Qualcomm Snapdragon 821 processor and 4GB RAM, not outstanding today. Calls are still the main function of a phone. Will Pixel XL make progress on this?

Just like most Qualcomm Snapdragon 82x series smartphone, the audio CODEC of Pixel XL is Qualcomm WCD 9335, responsible for audio sub-system including music playback, calls, etc. We can hardly find technology details of the WCD9335, but we are sure that the hi-end Qualcomm SoC smartphones have better average call quality than those with low-end SoCs, especially in hand-free mode. So, higher price, better call quality. Most Qualcomm SoC smartphones are adopting Fluence C Qualcomm's noise cancelling technology, including Moto X, Moto Z, and Pixel XL is not an exception.

Our Pixel XL is an unlocked version sold in the USA, so it just supports China Unicom FDD-LTE and WCDMA, not supporting China Mobile TDD-LTE. It sometimes will not switch 3G and 4G network automatically, we have to switch it manually. We cannot figure out whether this is because of the wireless network or Google. The design language of Android is similar to Android 6, except some colored contract list.

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 Pixel XL Nexus 6P Huawei Mate 9 Pro vivo Xplay 6 MOTO Z iPhone 7 Plus
Output Level of Earpiece,dB -8.7 -11.16 -11.88 -10.56 -18.43 -8.06

The earpiece speaker maximum volume is significantly lauder than Nexus 6P, similar to iPhone 7 Plus, and has a full vocal performance. From the recording wave graph, we can see that the frequency response is over 8kHz, which is limited by GSM, we suppose that the sound is processed, but not much contribute to GMS wireless network.

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 Pixel XL Nexus 6P Huawei Mate 9 Pro vivo Xplay 6 MOTO Z iPhone 7 Plus
Face Up,dB 72.1 77.6 74.1 78.1 74.1 78.9
Face Down,dB 72.8 78.1 77.7 78.3 75.2 79.8
In Camera Bag,dB 68.8 74.0 73.1 70.0 69.8 73.3

Pixel XL's loud speaker's volume is even lower than the Moto Z, which uses earpiece as a loud speaker. What's more, Pixel's loud speaker is placed in the bottom, compared with Nexus 6P's stereo loud speaker, it is regarding that Pixel XL is worse in volume and quality.

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[GSM Hand Holding] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction,dB[Higher is Better] 43.1 39.4 46.2 46.6 34.6
SNR Improvement,dB[Higher is Better] 30.5 26.9 34.7 35.3 23.9
SNRI-to-NPLR difference,dB[-4 to 3] -2.3 0.0 -5.1 -3.3 1.0
Testing Item[Hand-Free Mode] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction,dB[Higher is Better] 38.1 27.8 41.0 42.9 26.5
SNR Improvement,dB[Higher is Better] 27.5 6.0 28.3 31.5 15.3
SNRI-to-NPLR difference,dB[-4 to 3] -5.5 -7.7 -9.7 -6.3 -0.5
Testing Item[Nexus 6P] Noisy Crowd Background Music Pink Noise Roadside Voice
Total Noise Level Reduction,dB[Higher is Better] 40.0 35.4 41.0 41.0 35.9
SNR Improvement,dB[Higher is Better] 29.3 26.6 30.9 28.9 24.4
SNRI-to-NPLR difference,dB[-4 to 3] -1.8 -0.4 -2.7 -2.8 -0.2
  • 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.

Compared with Nexus 6P, under hand-holding mode, Pixel XL is about 1dB higher in recording volume, and a similar noise reduction performance, while Pixel XL is higher in hand-free mode in recording. Pixel XL has a better noise reduction performance than Nexus 6P, but under chaos ambient noise, it sometimes reduces the vocal signal. If using smartphones in cars or on the road with hand-free mode, Pixel XL is not as good as Mate 9 Pro, but significantly better than Moto Z.

Pixel XL is stable in Skype, WeChat and other VoIP recording, but its loud speaker's low volume has negative influence in calling experience. Compared with Nexus 6P, Pixel XL has a better hand-holding performance, thanks to the higher earpiece volume, while its loud speaker has a lower volume and a worse sound quality, brings negative influence to hand-free mode experience.

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