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We bought a Lenovo Phab2PRO to do some development of Android apps which take advantage of Google Project Tango's localization technology.

We are finding that not only our app (which uses AudioRecord), but several other apps (e.g. the default Sound Recorder app that came installed on the device, and a dB meter app, and a tutorial demo https://www.newventuresoftware.com/blog/record-play-and-visualize-raw-audio-data-in-android) all suffer from a behavior in which a loud sound input to the microphone is automatically attenuated somehow within about a second of the sound being on. (EDIT: A graph of this behavior is shown below.)

The tango device is running Android version 23 "Marshmallow"; which apparently does not support UNPROCESSED input (as per this post about Automatic Gain Reduction). We have observed this behavior the sources labeled DEFAULT, MIC, and VOICE_RECOGNITION.

(This behavior was not observed on an older Android device running Jellybean, but that lacks the Tango technology).

How do we turn this off? We have looked in "Settings", etc. This is crucial for our audio measurement app.

P.S.: AutomaticGainControl.isAvailable() returns False.

EDIT: When connecting an external microphone via the phone's TRRS jack, no such attenuation is observed. (Perhaps Lenovo installed some kind of compressor circuit with their onboard microphone?) We would prefer the convenience of using the onboard mic, but if an external mic is the only way, then so be it.

Update: We actually have two 'identical' Phab2Pro's that both exhibit this behavior. Spoke to Lenovo Support and the person on the phone wants us to send them in for repair. I'll send one in and keep the other to minimize 'downtime'; am curious if there is an unfixable design flaw with these internal mics circuits. In the meantime, would still love a 'software' solution if one exists!...Any ideas? :-)

EDIT: The following image illustrates this attenuation, which was made by playing a steady-state tone and changing the frequency (but not intensity) twice. Observe the fall-off in measured sound level despite the real sound level remaining essentially constant (this was made using the free "Sound Meter" app by ABC): graph of measured sound intensity vs. time

sh37211
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  • Got the Tango back from Lenovo repairs, still shows EXACTLY the same problem. Furthermore, we notice that the audio input (mic or analog jack) for these devices (both of ours) will "clip" for even moderately-loud sounds -- i.e., at 95dB SPL, the input saturates at the top of its range. This is unacceptable.:-(. We may look into using a dedicated mobile audio A/D / mic-pre. – sh37211 Jun 23 '17 at 20:07
  • Bought a Shure MVI external audio interface as a workaround, but the Phab2Pro wouldn't recognize it. Apparently despite boasting about Dolby Atmos capability, Lenovo/Google didn't endow it with USB Audio 2.0. – sh37211 Jul 07 '17 at 20:22

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