Tango suffers from unidentifiable automatic gain reduction

We bought Lenovo Phab2PRO to develop Android apps that use Google Project Tango localization technology.

We find that not only our application (which uses AudioRecord), but also several other applications (such as the default Sound Recorder application installed on the device and the dB meter application and training demo https://www.newventuresoftware.com/ blog / record-play-and-visualize-raw-audio-data-in-android ), they all suffer from a behavior where loud audio coming into the microphone automatically fades out about a second after the sound is turned on. ( EDIT: A graph of this behavior is shown below.)

The tango device runs Android version 23 "Marshmallow"; which doesn't seem to support UNPROCESSED input (as per this post about automatic gain reduction ). We see this behavior of sources marked as DEFAULT, MIC and VOICE_RECOGNITION.

(This behavior was not seen on an earlier Android device running Jellybean, but it lacks Tango technology.)

How can I disable this? We looked at "Settings" etc. This is very important for our sound measurement application.

PS: AutomaticGainControl.isAvailable () returns False.

EDIT: No such attenuation is observed when connecting an external microphone through the phone's TRRS jack. (Perhaps Lenovo installed some kind of compressor loop with a built-in microphone?) We'd have preferred the convenience of using the built-in microphone, but if an external microphone is the only way, then so be it.

Update: We actually have two "identical" Phab2Pro's that demonstrate this behavior. Talked about Lenovo support and the person on the phone wants us to send them in for repair. I will send it and leave another one to minimize downtime; Curious if there is a fatal design defect in these internal microcircuits. In the meantime, would still love "software" if it exists! ... Any ideas? :-)

EDIT: . The following figure shows this attenuation, which was done by playing a steady tone and changing the frequency (but not the intensity) in half. Observe the decay in the measured sound level, even though the actual sound level remains almost constant (this was done with ABC's free "Sound Meter" app):