So, the second part of this question, is that the music is based on a different musical system than the one we use today. So if you wish to “get it” you would need to listen to more of it.
This music is based partly on a system called “Modes”. This Modal system of writing developed from before music was written down, and can be first heard in the Psalm singing of Church and Monks.
Essentially it is music written in one key but co-allessing around different parts of the scale.
The music can be imagined as being on the white notes only of the piano, ie no black keys or divisions, (though again nothing is simple in music and this is not necessarily so).
As explained before. We use a system of cadences which were first developed in the Medieval period but which were changed to different uses in the Renaissance and beyond, ie the uses that we are more used to now.
The cadences in the Medieval period were about how to end pieces correctly according to which Mode you were in. Which led to our being used to the musical cue and therefore having something to hang onto when listening to the pieces. So first Modes.
C D E F G A B C this is the standard C major white notes that we use today. But originally was not used in this form, (it was originally called Hypolydian mode).
What the medieval theorists cobbled together from disparate and mistaken interpretations of the original Greek understanding of Modes was a system of 4 pairs of modes. These are tunes which cover an octave and have a final note. So the original cadences were from plainsongs, that monks are familiar with today, and are solutions to how to end a melody correctly.
Using the white keys only the 4 Perfect scales to use were.
Dorian D E F G A B C D
Phrygian E F G A B C D E
Lydian F G A B C D E F
Mixolydian G A B C D E F G
There are also 4 matching Imperfect scales which is another subject, so we will stick with the perfect.
Now the reason these modes sound different is down to an observation. If you look at the keys of the piano, you will notice that the white keys are sometimes together (EF and BC) and mostly with a black note between, this is because the pitch intervals between the letters are not all the same. E to F and B to C are a semi tone apart, and all the other letters are 2 semitones apart (we call this a tone (which apparently originally meant scale in Greek)). So if we apply this to our modes we get.
sT = semi tone T = tone.
We are used to this C major:
C D E F G A B C or C tone D tone E semitone F tone G tone A tone B semitone C
T T sT T T T sT
If we look at the four Perfect modes we get.
Dorian D E F G A B C D T sT T T sT T
Phrygian E F G A B C D E sT T T st T T
Lydian F G A B C D E F T T T st T T st
Mixolydian G A B C D E F G T T sT T sT T
So by shifting around a set of notes we can get a range of different melody styles.
Now for the learnt bit from the 10th century onwards various treatises said that the 8 (4 Perfect and 4 Imperfect) had particular characters, which were then used to chose which mode to use for which Psalm, depending on the words of the Psalm.
The Imperfect ones had the name Hypo added to the front. The names at the top are the Treatise writers Guido D’Arezzo 10C, Adam of Fulda 15C, Juan de Espinosa Medrano 17C.
happy, taming the passions
serious and tearful
inciting delights, tempering fierceness
tearful and pious
uniting pleasure and sadness
So hopefully this is making some sense of the Medieval sound world. Of course this is only amongst the wealthy and the Church as the normal peasants had their own music which on the whole is what we are used to now.