That's it, that's my new favourite word in Welsh now! It sounds so beautiful!
It's okay to pronounce, just do it really slow, and make sure you perform a small but firm set of rolled Rs and both forms of the dental fractives.
The preposition "ar" causes soft mutation in the following word, and so the C turns into its voiced equivalent G.
Thank you. So it would be "gwrando ar gerddoriaeth" (listening to music) and "gwrando ar y cerddoriaeth" (listening to the music)?
Not quite -- the noun cerddoriaeth is feminine and so it receives soft mutation after the definite article y, yr, 'r as well. (And would receive soft mutation after the indefinite un as well, if it made sense to speak of "a music".)
So it would be gwrando ar y gerddoriaeth.