From instrument of the bards which can be used as a bardic focus:
When you use the instrument to cast a spell that causes targets to become charmed on a failed save, the targets have disadvantage on the saving throw. This effect applies whether you are using the instrument as the source of the spell or as a spellcasting focus.
And from the spell compulsion:
Creatures of your choice that you can see within range and that can hear you must make a Wisdom saving throw. A target automatically succeeds on this saving throw if it can't be charmed. On a failed save, a target is affected by this spell.
The spell doesn't outright say the creature is charmed, but also states the spell doesn't work on creatures that can't be charmed, and the effect of the spell is similar to that of a charm spell (and uses the same saving throw to prevent it).