LG VELVET LM-G900UM User Manual page 31

There are two microphones built into this product. Be careful not to cover
the microphones. While you are talking on the phone, do not cover the
microphone with your hand or fingers.
Do not use a phone case that is not a genuine product or cover the
microphone with accessories, tape, etc.
Hold the product correctly as shown in the image when you are using it.
Microphone Do not cover the microphone.
Microphone Do not cover the microphone.
Basic Functions
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