You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Adult_contemporary_music

Context:
While most artists became established in other formats before moving to adult contemporary, Michael Bublé and Josh Groban started out as AC artists. Throughout this decade, artists such as Nick Lachey, James Blunt, John Mayer, Bruno Mars, Jason Mraz, Kelly Clarkson, Adele, Clay Aiken and Susan Boyle have become successful thanks to a ballad heavy sound. Much as some hot AC and modern rock artists have crossed over into each other, so too has soft AC crossed with country music in this decade. Country musicians such as Faith Hill, Shania Twain, LeAnn Rimes and Carrie Underwood have had success on both charts.

Question:
What sort of sound does the music of Susan Boyle have?

ballad heavy