This image shows the volume set on Android (57%) and that goes for Nextgen too.
Spoiler: Image
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This image is said that the volume is at 100%.
I imagine it is 100% of the volume set on Android (57%).
Spoiler: Image
[Only registered and activated users can see links. ]

This image shows that the system is completely silent.
Spoiler: Image
[Only registered and activated users can see links. ]