Last night I duelled a friend and did some research on this.

Background:

Jyzan - level 24 bard
Str 104
Dex 107
Cha 76 (I'm wearing a grotesque mask)

Singing: 125
Brass: 76
String: 125

When singing Denon's Disruptive Discord, it was doing 9 damage per tick. Chords
of Dissonance was doing 7. Denon's also decreased the target's AC by 9, which
is very good.

When playing their respective instruments, Denon's was going 19 damage per tick,
while Chords was doing something like 15. Denon's was also decreasing AC by 19,
which is a LOT. This is MORE than taking off a steel breastplate and going
barechested.

Keep in mind that these songs are "damage over time" songs, so that once you
make them "wince" once, it will damage them 2 more times, so if I were to juggle
these two songs and Brusco's Boastful Bellow, here are the effects I would have:

Tick 1: Denon's makes them wince for 9, and reduces their AC by 9
Tick 2: Chords for 7, Denon for 9, AC still reduced
Tick 3: Bellow for 13, Chords for 7, Denon for 9, AC still reduced.

The net result of all this: 54 damage, AC reduced by 9.

Compare this to most people's tactics, which is Bellowing all three rounds, for
a net damage of 39 and no AC reduction. Over a long fight, this is a
significant difference.

One other thing that we tested... Largo's Melodic Binding, in addition to
reducing attack speeds, lowered AC by 6.

Jyzan