The sixth volume in the highly successful Celtic Twilight series of compilations is a further indication that these albums have gradually moved from the new age/Celtoid end of the Celtic spectrum to a place where traditional music holds stronger sway. And so there’s Arcady and Dolores Keane shining brightly here, along tracks like “Forest Hymn,” which does possess a beauty of its own but lacks the power of songs that have existed for hundreds of years. The fact that pipers and whistlers like Liam O’Flynn and Paddy Keenan can make it onto something like this is very heartening, because it means their older styles are being widely accepted; that they fit next to a group like Capercaillie, who straddle the fence between new age and Celtic, shows how much the music has developed. More than its predecessors, Celtic Twilight, Vol. 6 demands a little from the listeners — but gives back a lot.