You can create a SoundCue asset and use CrossfadeDistance node as described here https://docs.unrealengine.com/latest/INT/Engine/Audio/SoundCues/NodeReference/index.html#crossfadebydistancenode
You can create a SoundCue asset and use CrossfadeDistance node as described here https://docs.unrealengine.com/latest/INT/Engine/Audio/SoundCues/NodeReference/index.html#crossfadebydistancenode