Well, there are actually two kinds of singing that traditionally are called 'canu penillion': dull y Gogledd (Northern style) and dull y De (go on - guess! yep: Southern style). What breezy mentions is the Northern style and has become highly technical. I recently was talking to one of the penillion 'greats' who was lamenting that Musicians are making this art so terribly inaccessible to the common person. Perhaps we'll be looking at putting together a workshop to try to combat this ... I don't know how it might work in English because the accents of Welsh tunes are geared to the accents of words (just as in any culture, I guess) but there are probably ways ...

The Southern style is a matter of singing a winding repetoire of verses to a given tune - no counterpoint or anything as in the Northern; the idea is to find as many verses as possible to the meter. Also, it is quite often interlaced with an instrumental refrain: Deck the Halls is a good example of this. There's a very high proportion of the Welsh repetoire where you have 'twiddly bits' between lines of the verses.

Sain records brought out a CD by Arfon Gwilym last summer (titled, I think ... Procio'r Tan) and there are examples of both on it. I think it's a great album as Arfon is trying to bring the art back into the folk domain.

You might take a look at the thread I've just started about 18th c. fiddler tune book. There's some info in the book about a fiddler's perspective on accompanying song ...

If you want a real shock to the system, a duo called Bragod is trying to take the art back to medieval roots, or at least mindset, of 'declaring' poetry to the music of the crwth. Of course, that's where this 'singing verses' got it's start.

siân