Two days ago I published a choral prelude by Friedrich Wilhelm Marpurg and called the accompanying post "A study in writing a choral prelude" (see here). My descrption of the proces was perhaps a bit dense.
You start with a four part harmonisation of a choral melody. Than you leave the notes for the bass voice and the soprano voice the same. And you take the notes for the alto and tenor voice to create a lince that moves in eigth notes between bass and soprano.
So I thought I'd elaborate a bit about the procedure. And the proof of the pudding is of course in the eating, so let's see whether the procedure really works.
Marpurg starts with a harmonisation of the choral melody. With this I mean that he adds the appropriate chords to the melody. This is an art in itself, that I wont go into now. Classicaly, harmonisation is written in four parts, meaning that each chor consists of four notes. Singing is the basis of al music, and four part harmony is derived from choir singing. One note for each of the four voices of a choir: soprano, alto, tenor and bass.
The choral melody is in the upper voice, the soprano voice. The bass voice provides the fundament of the harmony. The note that the bass sings determines the chord. Alto and tenor voice just fill in the harmony. Now we strip out the alto and tenor voice.
And the deleted notes will form the building material of the voice we want to create anew. A voice that moves in eigth notes to provide some motoric drive. The first half bar is an e major chord. And the characteristic note in a major chord is of course the major third. So we need something with the noes e, g sharp and b.
The next chord is an a minor chord, with the minor third (the note c) in the bass. Usually, in a four part harmonisation, the third of the chord is written only once. To make up a four note chord from a major triad, one of the three notes has to be doubled. And usually that's either the base note of the fifthe. An a minor chord consists of the notes a - c - e. The "c" is already in the bass voice, the "a" is the melody note, so that leaves the "e" and possibly the "a" for the voice we are writing. But in this case the "a" can not be used, because in the previous bar tha last note of both the soprano voice and the extra voice we are writing is an "e". And they cannot both move to "a", as that would create a paralel octave, and writing paralel octaves is not recommended (in classical harmony theory: it is "forbidden"...). So that leaves the "e" as the only possibility. Obviously Marpurg thought 'okay "e" it is' and he ties the "e" over from the previous bar and then repeats the chord notes "e" and "a".
The next chord is an e major chord, with again the major third in the bass voice. That leaves the "e" and the "b" for the middle voice we are writing. Now Marpurg does something a bit unexpected. He throws in a notes that does not belong to the chord. The middle voice stays around the "e" and to maintain the motion of eigth notes, Marpurg places a d sharp in between as a kind of auxiliary note.
And so marpurg goes on. The next chord is an a minor chord with the lowest note, the "a" is the bass and the minor third in the choral melody. And now Marpurg does double the minor third briefly. There are reasons why in this case a doubling of the minor third is acceptable (having a lot to do with the fact that it is a minor third), but I won't go into them. The chord after that is a d major chord, with the major third in the bass. Marpurg can't double that in the middle voice. So he does the same as he did in the previous bar: he throws in an auxiliary note, in the case a g sharp. And this nicely illustrates the two opposing forces that make music so interesting. Be surprising ánd be consistent. Create something new and create something recognizable. Be creative and adhere to rules. Create the unexpected ánd create form.
The initial plan was to now use this procedure to create something of my own. But this post is already long enough as it is. So I'll leave that for a new post.
