Lute of Muting

When played by a bard, in addition to the standard bardsong bonuses, this instrument reduces the amount of Sonic damage dealt to all party members by 2. It does not matter if the Sonic attack is targeted at an individual or affects multiple victims, as long as the bard is performing bardsong with this instrument and the recipient of the damage is a member of the party, the Sonic damage is reduced.

Q: What happens when a bard switches instruments?
A: It depends.

Scenario A
Round 1
Monster wins initiative, makes sonic attack
Party’s turn, bard plays this instrument
The damage is not mitigated because the bard was not playing this instrument at the time of the attack.

Scenario B
Round 1
Party wins initiative, bard plays this instrument, but wants to switch to a different instrument the next round and informs the DM of this intention
Monster’s turn, it makes a sonic attack
The damage is mitigated because the bard has not actually switched to a different instrument yet.