This is the syntax for the /playsound command in Minecraft:
/playsound (sound) (source) (player) [x] [y] [z] [volume] [pitch] [minimumvolume]
The [volume], [pitch], and [minimumvolume] parameters are automatically set to their defaults if left blank upon execution.
The default for [volume] and [pitch] are both 1. What is the default for [minimumvolume]?
[minimumVolume]might refer to the lowest volume it can get to when someone is walking away from the source of the sound. I might be wrong, but it's what I understand it to be