Having the pleasure at the moment accompanying a 120 pce choir (satb). One song (Swing Low) gets a start pitch, but after 2 choruses, a capella, will drop at least a semitone, sometimes two. Why does this happen, and more pointedly, what can be done to rectify it? It's an experienced lot of singers, so probably shouldn't happen, but it does!


5 Answers 5


Karel van Steenhoven has an article A Practical Guide to Intonation and Tuning about how to avoid the intonation drop.

The phenomenon has been used intentionally in some pieces but I don't remember which.

It's a consequence of the Catalan Conjecture (no power of any prime is close to that of any power of another prime except for 0, and only 8 and 9 are close.)

One method I have considered (but never worked on) would be to take some pattern (Wiki suggests I-IV-ii-V-I can drift if the chords are in Just Intonation) as a test case. Instead of moving chord by chord as closely as possible, one should make sure the I chords are correct and correct in both directions (a discrete version of boundary conditions instead of shooting). Adjustments may occur and not-so-obvious places. As suggested in the comments, dissonances are good targets for slight mis-tunings as a dissonance suggested movement anyway.)

  • What does the Catalan Conjecture have to do with intonation?
    – Aaron
    Commented Dec 16, 2023 at 1:54
  • 1
    One cannot stack any number of octaves to get any number of fifths; one can get close but at the cost of really big denominators. No rational (based on ratios) system can match all the intervals one might want. In Just Intonation, two major seconds do not stack to make a major third. Tuning a guitar to perfect fourths with a perfect third inserted doesn't give 2 octaves. Some compromise must be made. According to Helmholtz's work, larger denominators in an interval's ratio tend towards dissonance.
    – ttw
    Commented Dec 16, 2023 at 2:22
  • 4
    What I meant was: you should explain in your post the relationship, including how the problems of just intonation lead to dropping in pitch. (Secondarily, I suggest adding this as an answer to the proposed duplicate.)
    – Aaron
    Commented Dec 16, 2023 at 3:25
  • 1
    I thought this kind of drift only drops music and singers by less than a semitone, not one or more semitones like the question claims.
    – Dekkadeci
    Commented Dec 16, 2023 at 7:37
  • @Dekkadeci a single comma is between a fifth and a quarter of a semitone, but if it happens four times in each verse and you sing two verses, voila, nearly a whole tone. In practice, though, this tendency varies, being more of a problem at some rehearsals than others, with the most significant factor seeming to be the weather (this is not a joke), so the structure of the arrangement can't be the only cause.
    – phoog
    Commented Dec 17, 2023 at 12:20

The Pythagorean comma is an interesting explanation, but it can't account for just HOW flat a choir can go and HOW quickly!
I am currently leading a small community choir through a series of Christmas concerts. Starting off with a simple 2-part a capella female version of 'Silent Night'is dramatically effective. But if we start in C, we end in B♭. No complicated reason, I think. Just breath support and a lack of confidence in going for the higher notes. If I sing with them, they stay in tune. And we can improve in rehearsal. It's just lack of confidence in performance.

  • 1
    Have you tried starting them in Bb?? Most of them wouldn't notice the difference, and would they tend to drop more, or is Bb where they naturally sing it anyhow..? With school choirs, I used to start that in key A, and modulate up to Bb. Key C always seemed just that bit too high. I was forever changing the key to suit the singers. An easier option.
    – Tim
    Commented Dec 16, 2023 at 15:22
  • 2
    Yes, there are ways to cobble round it. They sing SOME bits of it naturally in Bb :-) And then the men would have a low F in the second verse. And I don't really want a naff 'truck driver key shift' in this one! Maybe surprisingly, when I HAVE just played it, unannounced, in Bb they DO notice, and the sopranos complain I'm making them sing too low. You can't win sometimes!
    – Laurence
    Commented Dec 16, 2023 at 17:58
  • C is way too high, I do it in A, and it works relatively nicely. But I guess your choir are native English speakers, it gives around +2 semitones or more, compared to ... some other people. Commented Dec 17, 2023 at 1:34
  • In my experience, when a choral group is constantly dropping in pitch on a given piece, especially if it is "just one of those days" where the problem seems to arise suddenly after several successful rehearsals without it, starting the piece one semitone higher (in the hope that they drop to the "correct" pitch) typically leads to the group staying one semitone higher, i.e. no longer dropping in pitch.
    – phoog
    Commented Dec 17, 2023 at 12:18
  • @phoog - The arrangement already has 2 more key changes - don't really want to introduce another - although I have considered starting them in F# rather than F. Wonder how many would realise..? Sounds drastic and unfair though. Just my luck for them to stay in F#!
    – Tim
    Commented Dec 19, 2023 at 12:31

As an (amateur) singer, one of the things I've found helps me avoid drifting (usually downwards) in pitch is to consciously listen to the other parts — especially the top part (which is often the melody).

My theory is that it's often the lowest part (usually the bass or second bass) which tends to drift downwards, and that the higher parts then follow (like subsidence in a building).  I suspect we subconsciously base our tuning on the lower parts (which is why if there's a discrepancy between parts, it's the top/melody part we're more likely to perceive as being out of tune); hence the lowest part is left without a reference.

(Of course, that wouldn't explain why they tend to fall in pitch, rather than rise.  Maybe when we hear a range of tunings, we naturally tend to fixate on the lowest?)

It can take some concentration to listen to tuning of the top part — especially if you're surrounded by people singing your own part, and the top-part singers are a way in front of you! — and try to use it as a tuning reference, but I find it helps me more than anything else.

  • Good point about the sopranos being in front, hence difficult to pitch from. Be interesting to re-arrange the satb physically... Can't find a reason why basses/tenors are always at the back. Maybe another question!
    – Tim
    Commented Dec 19, 2023 at 12:21
  • In my experience, if you want a really well-blended, in-tune sound, then you don't group the different parts at all, but mix them all up together.  That makes it easy to hear all the other parts, as they'll be much closer to you; and being further from people singing your own part makes it easier to hear yourself, so you can better judge how you fit in.  — However, it only works if all singers can hold their line, which not all amateur singers are happy doing.  (It also needs a fairly homophonic texture.)  So it doesn't happen anywhere near as often as I'd like…
    – gidds
    Commented Jan 28 at 0:41

Why does it happen? Well, intonation is hard. There are certain things singer tend to naturally. Semitones are often overestimated, leading to people singing them smaller than they should be. Whole tones are underestimated, leading to people singing them smaller than they should be. This might differ when singing up or down. And suddenly even when singing a simple scale you might end in a different key than you started with.

It is generally also a matter of tension. If you are too relaxed you tend to fall, if you are too tense you tend to rise. Intonation is also about finding this balance.

What can you do? One thing is practice. The more experienced your singers are the easier it will be for them to intonate. But also a good warmup is important, as well as the energy the choir conductor radiates into the choir. In your case the singers might be tired. Try to activate them more in the warmup and maybe also between the pieces.

  • Strange - it was bad in a rehearsal, but spot on in the last two concerts. One more to go, so we'll see (hear!) what happens then. I'll report back.
    – Tim
    Commented Dec 19, 2023 at 12:28
  • @Tim The choir is probably more relaxed during rehearsal, so the intonation drops. Wish you great success on the last concert!
    – Lazy
    Commented Dec 19, 2023 at 20:49

My suggestion to the original poster -

I have also been in an acapella at my school, based on a Tamil film number. I also had a similar experience to you.

What we did was - we made use of the shruti box / drone / tanpura, made everyone listen to the sruthi / pitch, and align themselves along with the sruthi / pitch, so that there are no drops and everyone is in sync with the pitch.

It should work for you too.

You can search on YouTube for 'tanpura sruthi' in your required pitch.

Believe me, it works wonders!

Also it is an absolute must while practicing. Some source where the pitch that you sing in is constantly played will keep you in tune.

  • 1
    To the person downvoting: May I know how I can improve? Commented Dec 20, 2023 at 12:38
  • Is the drone loud enough for the audience to hear?  If so, presumably it's only appropriate for pieces written with a drone, or at least where a single note would be in harmony with every moment of the piece?  (Which would seem to rule out the vast majority of Western music, for instance.)  Or if not, how is it loud enough for all the choir to hear sufficiently, even while singing?
    – gidds
    Commented Dec 22, 2023 at 20:17
  • 1. The drone has to be amplified using a Bluetooth speaker or some equipment. 2. As for harmonies, all the groups doing the harmonies should be able to practice their individual parts and put it together without confusion, for the group on the main will be dominant. Commented Dec 23, 2023 at 1:18
  • Audience may hear or may not hear. That's not a problem. The main thing is that all the choir members need to hear. Commented Dec 23, 2023 at 1:19

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