I wonder if someone can tell me whether there is a convention when laying out a lyric to show different parts (or even a chorus). In my novel, there are a number of poems and lyrics. They are set in the usual style of indented and italicised. However, some of the poems/lyrics are sung by different people and it's important to distinguish the two parts. Is there a convention for doing this? I don't see it dealt with in any of the style manuals I have thus far consulted.
This is how Tolkien solves a similar problem in The Lord of the Rings:
When Spring unfolds the beechen leaf, and sap is in the bough;
When light is on the wild-wood stream, and wind is on the brow;
When stride is long, and breath is deep, and keen the mountain-air,
Come back to me! Come back to me, and say my land is fair!
When Spring is come to garth and field, and corn is in the blade;
When blossom like a shining snow is on the orchard laid;
When shower and Sun upon the Earth with fragrance fill the air,
I’ll linger here, and will not come, because my land is fair.
When Summer lies upon the world, and in a noon of gold
Beneath the roof of sleeping leaves the dreams of trees unfold;
When woodland halls are green and cool, and wind is in the West,
Come back to me! Come back to me, and say my land is best!
When Summer warms the hanging fruit and burns the berry brown;
When straw is gold, and ear is white, and harvest comes to town;
When honey spills, and apple swells, though wind be in the West,
I’ll linger here beneath the Sun, because my land is best!
J.R.R. Tolkien, The Lord of the Rings, Book III, chapter 4 - Treebeard
I am fairly sure that in another book I've seen something along the line of:
Alpha sang [...] then Bravo took over [...] and they finished together [...]
In the second variant the interruptions draw a bit more attention to themselves, but at the same time they make better sense in terms of the narration: if you imagine the story being "told", you wouldn't expect tags as in the first example.
The reason you haven't found this in any style manual is that if you're writing a novel (or a short story - doesn't matter), this is really up to you. There is no one single convention. There are multiple solutions that can be employed. Depending on what fits the overall style and voice of your story better, you can pick one approach or the other.
I think you will find this a matter of formatting style that is unusual enough not to have a convention. Certain publishers of music might have guidelines for it (can't help you there), but in a book you can probably present it as you wish. A publisher may choose to format it differently, as with most formatting details, but if you start with something you like I doubt you'll go wrong.
I would suggest that you check out the book Joyful Noise: Poems for Two Voices, by Paul Fleischman. These are children's poems about insects with the two voices given separate columns, intended to be performed aloud (like music would be). This is helpful for the many overlapping lines the voices share, and you can see how it works on the page.
If you don't have overlap, or only sections such as the chorus with both voices, you can use the format in Galastel's example.
Alternatively, with no overlap you might choose to right-justify one voice's lines, or put them in italics, with some indication only at the beginning of who has which part.
You are writing a novel, and @Galastel's second example explains how you may use conventional dialogue tags to label the different speakers of different parts of song lyrics.
In poetry, commonly the dialogue tags become part of the poem. Here is the beginning and end of a poem by Robert Bringhurst as an example, with the dialogue tags emphasized by me:
These poems, these poems,
these poems, she said, are poems
with no love in them. [...]
These poems, she said....
You are, he said,
That is not love, she said rightly.
I've seen this done several different ways.
- Chorus in bold (typical in printed lyrics to be sung from if everyone, including the lead, sings that part together)
It was in nineteen hundred and twenty nine
Run come see
I remember that day pretty well
Nineteen hundred and twenty nine
Run come see, Jerusalem
- Chorus in parentheses (typical if the lead does NOT join in the chorus and/or overlaps with it).
It was in nineteen hundred and twenty nine (Run come see, run come see)
I remember that day pretty well
- Singers in separate columns (this makes a nicer presentation for a book, where you're primarily just reading the lyrics, but you want to give a sense of what is being sung together.)
LEAD CHORUS It was in nineteen hundred and twenty nine
Run come see
I remember that day pretty well Run come see It was in nineteen hundred and twenty nine
Run come see, Jerusalem
- In the style of a script
Lead: It was in nineteen hundred and twenty nine
Chorus: Run come see, run come see
Lead (overlaps chorus): I remember that day pretty well. Nineteen hundred and twenty nine
Both: Run come see, Jerusalem
Given that there's no one standard method, you can use the one that is best fitted to your needs.
For reference: Run Come See, Jerusalem
I have a trinity of methods for whenever one is wondering how to visually display different ways/forms/voices of communication, whether that be distinguishing dialogue, thoughts or telepathy (basically thoughts present in POV mind though by a different character). In this case, there is one form of communicating, singing, but two different voices in that communication.
So, here are the three different methods:
I always and solely use them for thoughts. Few things in art are objective, but I believe it is objectively better to use italics for thoughts. Anyways, they can be used as a general way to distinguish one form of communication from another.
I personally use this, combining it with the italics. In my book, there is POV character possessed by a demon. The POV's thoughts are written in italics, but since the demon's way of communication is through the POV's mind, his speech is also in italics. So, how do I distinguish the two voices? With a different font for the demon. Not only is this effective, but it allows for some stylization of the character in question. I use a dark and jagged font for his dialogue, and it fits his demonic personality quite well. Font use is a definitively effective for visual story-telling in your writing.
Does your text come from the left? The right? Does it run down the middle? This is another visual way to distinguish different forms/ways/voices of communication. I usually use this for singing, adjusting the text to center alignment. Now, there are probably more ways than the ones I have mentioned, and the ones mentioned might not work for you, for whatever reason. But keep exploring. I've read a guy who has many different ways of communication, and he uses none of the methods mentioned. (He uses brackets, "-" and '-')
tl;dr: Look at the highlighted words