Okay, so it’s ultimately in the hands of singers whether they produce in-tune performances, but arrangers can have more of an influence on how well they achieve this than you might think. Here are three factors that can affect how well singers tune:
Refreshing static lines. So, we know it’s a standard rehearsal technique to ask singers with repeated notes to think of singing each successive note a bit higher than the last as a means to counteract what seems to be the natural effect of gravity on pitch. This rather suggests that we can avoid people having to use this rehearsal technique by being sparing in our use of long strings of repeated notes. In close-harmony arranging, this is most likely to tempt us when there are slow-moving harmonies and/or a melody and accompaniment texture – but there are things we can do to keep the singers rejuvenating their relationship with pitch.
For example, in an arrangement of Take That’s I'd Wait for Life for soloist + female chorus, I originally had the opening accompaniment looking like this:
But clearly that was going to be both dull to sing (if easy to learn!), and liable to sag. The final version has exactly the same notes in it, but a more interesting experience for the singers, and keeps them in a more active relationship with pitch:
Keeping leaps within the harmony. As a rule of thumb, the harmony parts should move by smallish intervals wherever possible, so as to keep the melodic attention on the tune. But leaps are needed periodically, especially in the bass, and sometimes in the baritone and/or tenor too. You are most likely to hear leaps tuned accurately if you place them within a single harmony – i.e. as a re-voicing of the prevailing chord – rather than across chord changes.
So, in this example from Cry Me a River, the bass has an octave leap, and both tenor and baritone leap up a tritone within the chord of A flat 7 on the words ‘whole night’.
Voicing for good balance. This is mostly an issue when the melody goes somewhere other than the lead – since, when the lead has the melody, it’s predetermined what note it will have (duh). So, it comes into play in situations like the soloist+chorus texture above, or in bass melody sections. In these circumstances, lead and baritone are both inner parts of pretty much equal pitch, and it would seem on the face of it that either part could take any of the inner notes in the chord. However, given that a chorus will usually have more leads than baritones, and a quartet lead will be accustomed to taking a prominent role in the balance than the baritone, we can use these habitual volume relationships to make decisions about voicing.
The key thing here is to give the louder part the notes lower in the harmonic series – roots and 5ths rather than 3rds or 7ths. For example, some friends from IABS recently commissioned this arrangement of Embraceable You as a bass melody, so I’ve given the lead the 5th and the bari the 3rd at the opening.
Often if you hear what sounds like a slightly flat major 3rd, the problem is at least partly that it is an over-loud major 3rd; you can fix the tuning by getting the chord more into balance. So, as arrangers, we can save the groups we write for rehearsal time by building the harmonies in such a way that the group’s habitual balance is the one needed for optimal tuning.
This is not an exhaustive list, of course – and I may return to this subject at a later date!