Some of the authors chose music which came from the period in which their novels are set. It's not so easy for me to do this, as my writing is all set in the pre-Conquest period. I do have a CD, however, which attempts to give the flavour of the music of the time, and it can be quite useful for creating atmosphere.
Sanctus seeks to recreate the sounds with which Bede might have been familiar, taking traditional plainchant and adding harp and pipe.
It's fair to say, though, that this is probably not a true representation of the music of the time. Few musical instruments have been unearthed from this period, possibly because they were mainly made from wood. Flutes made from applewood and hawthorn were unearthed from the Anglo-Scandinavian levels at York  but where the soil composition is not so conducive to the preservation of such items, they will have been lost. The sound would be more sonorous than those made of bone:
Some flutes were also made from the bones of swans' wings.
The other main musical instrument that we know about is the lyre, referred to in the sources as the harp. The most famous of all these finds is probably the Sutton Hoo lyre, but it is rather more ornate than those which would have belonged to a 'jobbing' musician, or scop. It was made from maplewood, and had six tuning pegs. The sound board was secured using pins cut from a strip of sheet copper alloy 
The highest level of woodworking skills were required to make the instruments. A lyre has two main elements, the sound-box and the yoke into which the tuning pegs were seated. The lyre at Sutton Hoo had a 16mm deep soundbox carved from a single piece of maple. The soundboard, 3mm thick, was nailed over it, and the joints used to fix the yoke to the arms of the sound box were 'bridle joints', not 'mortise and tenon' 
|Replica Lyre at Sutton Hoo - authors' own photo|
Scops, the poets and singers, would have played the harp, but it seems that others were expected to have playing skills, too. Important occasions were marked by feasts, accompanied with music and entertainment. According to Bede, "When a cause for celebration had been determined ... they must all sing with a harp in turn."
However, stage fright appears not to be a modern phenomenon. "Whenever all those present at a feast took it in turns to sing and entertain the company, he would get up from the table and go home directly he saw the harp approaching him." 
Another instrument was the handbell, made from iron and primarily used for cows, but also used by Irish monks in the early Christian period. The figures below are depicted at Edward the Confessor's funeral (Bayeux Tapestry)
Much mention is made of the power of song. "That every day he heard the pleasure loud in the hall, the scop's clear song." (Beowulf 1.86-9)
It seems that there were different types of song: giedd (narrative and often sad), the leoð (also narrative), folcræden (tribal tradition) 
It's possible that as well as being played and sung in the hall in the evening, the scop's music was also used to rouse the slumbering warriors the morning after - a precursor to the alarm clock!
It's clear that music, and particularly song, was important. From Widsiþ:
...and I with a bright voice, raised a song for our victorious lord. Loud with the harp the sound mellowed, when many men, proud with mead, spoke their words,who well knew, that they had never heard a better song."
We can't be sure what any of this music sounded like, but we have a little information dating from the end of the period. The Winchester Troper dates from around AD1000 and includes possibly the oldest written music, designed to be performed in Winchester Cathedral. A sample can be heard on YouTube.
Here's a recreation of what multi-instrumental music might have sounded like:
and a demonstration of music played on replicas of instruments found together as grave goods.
The theme of this series of blog posts has been Writing to Music. For all the reasons stated above, it's hard for me to do this in the way that some authors can. If music inspires me, it's usually the lyrics which spark my imagination. Lyrics, for me, are a bit like the poetry of Tennyson: an elegant yet simple summation of the things we all feel, but struggle sometimes to put into words. Songs often dig down and expose the centre of my characters' situations. If you've read my books, then you'll know who I'm talking about:
Chasing Cars - Snow Patrol: sums up how Æthelred of Mercia feels when he's tired of the struggle and wants his wife to just be with him, supporting him. (To Be A Queen)
You're Beautiful - James Blunt: simply a perfect way to describe how Alvar feels when he first meets Káta. (Alvar the Kingmaker)
Leaving the Land - Mary Black: a wonderful expression of Káta's belief that you can't go forwards in life if you're always looking behind you. (Alvar the Kingmaker)
I can't make you love me - Bonnie Raitt: a pivotal moment in the lives of Edwin and Carinna. (Cometh the Hour)
Angel - Sarah McLachlan: this track happened to be playing while I was writing one of the saddest scenes of Cometh the Hour. If you've read it, you'll know.
None of these tracks is remotely medieval in sound. But emotions are timeless, aren't they? However, there is something which bridges the gap between authentic Old English music, and the atmosphere conjured up by those artists and writers attempting to recreate the past. So, fianlly, enjoy this video and the accompanying music.
Amazon Author Page
 Wilson, 1976, (Quoted in The Mead-Hall - S Pollington)
  Anglo-Saxon Crafts - Kevin Leahy
 Cædmon's Vision, Translation by Kevin Crossley-Holland
 Bloomfield & Dunn 1989