Being able to transpose keyboard music at sight is a useful, if impossible, skill for any budding organist or repetiteur. One finds that, many a time, a choir or congregation is not able to sing a piece of music, usually a hymn, at the desired pitch; therefore downward transpositions of a semitone, tone or minor third or common. An (church) organist may also be instructed to transpose a hymn in order that the key may be closer to the key of the voluntary at the end of the service.
After intensive (i.e. tenuous) study of transposition at the keyboard, I have identified four main ways of accomplishing this task. They vary in difficulty, and, to some extent, in "correctness".
- The simplest method to achieve a transposition of up or down one semitone is to just imagine sharps, flats, or naturals (as necessary) in front of all the notes. So for example, were a hymn in D major to be transposed down one semitone, the organist can just pretend that the key signature has 5 flats (D flat major), and also remember to play C's and F's natural when he comes across them (as they are sharps in the original key of D major). Drawbacks of this method are that it only works for small up-or-down-one-semitone transpositions. Benefits are that it is perhaps the easiest method described here.
- The next method is in some ways a generalisation of the previous way; instead of imagining sharps and flats, the player imagines that the notes on the page have been physically moved up or down by the required interval. Drawbacks are that it gets too complicated beyond a transposition of 1 tone in either direction; and sharps, flats and naturals in the original key signature can too easily foul things up. Note that this is probably the default method of transposition for almost all new organists, and perhaps inexperienced organists in general.
- The third method is also perhaps the most idiosyncratic. It is as follows: observe that, once you have memorised a melody, it is possible to sing it back to yourself in any key; regardless of the note you choose to start from, your brain finds it perfectly easy to reconstruct the melody in real time (this also applies to people with absolute pitch – it is the memorising that counts). Therefore, if you are transposing a hymn that is fairly familiar to you, it is possible, if a little contrived, to play through the hymn in your head in the new key, perhaps glancing at the music here and there for a memory aid for some of the chords, and play the notes on the keyboard based on what notes you have in your head. A drawback of this method is that you are unlikely to have memorised perfectly all the chords of the hymn in addition to the complete melody, so this method perhaps only works for hymns that you know particularly well.
- The final method is generally held to be the most "correct": as you play the hymn, you note the interval between each successive pair of notes, and move your fingers on the keyboard by that interval to the next note; the idea is that you ignore the absolute pitch value of the note, and so having started the hymn in the transposed key, everything thereafter is played at relative pitch. This method requires a lot of concentration and/or experience, but, once learned, is (at least in theory) just as easy for transpositions of a semitone as it is for, say, a diminished fifth.
It is expected that as you learn how to transpose, you tend to gravitate towards the more "correct" method (the fourth one in the list) – though it is important to note that due to the extreme difficulty in calculating the interval in every part in real-time and transferring that to the intervals on the keyboard, various other techniques must be employed: recognising the general shape of a chord and identifying it e.g. as "dominant, first inversion"; taking advantage of "free gifts" – notes that do not change in a particular part between two chords (sometimes not even two adjacent chords: experienced practitioners will be looking several chords ahead to find notes that do not change that they can use as "free gifts").
A final note: remember to choose a steady tempo and stick to it; don't dive in straight away with a transposition of a compound augmented fourth – have a go at small shifts on the order of one or two semitones (and start with method 1 above) – it's all good practice in the end.