singing harmony is two or more voices in notes of a key-at the same time. I don't know if that is the "proper" definition but it gets the job done. Technically I guess you could be singing the same note, but 'harmonizing' seems to be in different notes of the same chord or key.
so really it's vocal instrumentation, in this context. Although a band can use a guitar for harmony like Thin Lizzy or even Iron Maiden used to use dual lead guitars for the harmony, playing the melody of the songs. Like 'Whiskey in the Jar' has that dual lead riff throught most of the song, techincally that is a harmony. There are also examples of two lead guitars playing different notes, I am struggling to think of one.
like even when Bono overdubs on Yahweh or Even Better than The Real Thing, technically that would be 'harmony' even though it's only done in the studio. Live U2 has a lot of harmony, Lemon-'midnight is where the day begins' Edge singing the lower register and Bono singing the high.
Examples are all over, pretty much when Edge sings, he is singing some type of harmony to Bono's singing. Like when he sings 'Always' in Beautiful Day, that is harmonizing, or when he hits the high 'Stay' during the live acoustic versions.
it's not that hard with two singers who can actually sing, and especially in proper pitch. The difficult thing would be to actually 'harmonize well'. Which means, like Simon and Garfunkel, sounded good because Paul Simon has an average voice, but he always song the lower register, so Art Garfunkel took the high, and they offset well and it sounded nice, I think. There are better examples of U2 harmony, I am just going off the top of my head.
I think one that is spectacular is in Native Son's chorus, although they aren't signing it at thte same time, they are playing the voices off of each other, so to me that is harmonious.
Like for instance, I LOVE the Beatles harmony, John and Paul as well as Queen and Alice in Chains have awesome harmonies, but I can't stand the Beach Boys. Even the Bee Gees had spectacular harmony, but I can't stand Crosby, Stills and Nash.
For example, John and Paul sang in the same key sometimes, I Wanna Hold YOur Hand, but it's still harmony. And the Beach Boys had some god awful mis-mash of notes, that doesn't appeal to me, but I'm sure some people love it.
So like anything, it's a matter of how it appeals to you. I mean obviously something out of tune, is not going to sound harmonious or even 'good' for that matter.
But I don't think it's that hard for singers who can sing in pitch.
Most dudes in a rock band probably aren't great singers to begin with, but even if they are they have to sing to the song and not affect their voice to take it out of harmony.
For instance, if you listen to the low track in Even Better Than the Real Thing, it's pretty much monotone, more or less, but it works because Bono overdubs it and sings the melody in the higer register. It wouldn't work if his lower voice track was going all over the place, which is back tp the Paul Simon example.
Perhaps Queen is the best though, absolutely stunning harmony.
More or less it's notes of the same chord at the same time.
Vocally, I guess the reason that it is hard for bands to do is most men, on average have about the same pitch to their voice, most rock singers are probably a baritone. Which is between bass Tom Waits? (very low) and 2nd tenor (which is Bono). Tenors are either absurdly high Freddy Mercury, or Bono (2nd tenor) which is probably a notch right below. And yeah he can hit those notes too some times. I am not a vocal expert, just bored and rambling.
I am maybe speaking out of league here, but what the hell. I think Edge being probably a baritone like most rock singers. Bono being a 2nd tenor, really offsets him well, so it sounds good. If you have two tenors or two baritones, it can work but has less chance of working well? Something like that. Probably just comes down to knowing how to harmonize.
And thats really the only thing that is the dead giveaway is when it sounds bad, and that's usually because one of the singers just doesn't know how to harmonize even if they have an otherwise good voice.
