Stephen, you are right in that 作家 is referring to the profession, while 作者 is referring to the author of a piece of writing. And i don't usually see people use 作家 to cover song writers. Hope it helps. - Eddie

Yes,you are right. The two words have no obvious difference in the most of the time."作者" 's range is larger than "作家”。The latter often be used in the creation of literature. And "作者” roughly means a framer of something. So "作家" refer to a writer of of books/novels/non-fiction etc. while 作者 can also mean the writer of a piece of music (like composer).但如果是创作音乐，我们更习惯说“作曲家”。 I hope my answer can help you.

舉例來說 J. K. Rowling是一位[作家 ] 哈利波特的[作者]是J. K. Rowling ----------translate-------- for example J. K. Rowling is an author. Harry Porter is written by J. K. Rowling.

作家 is an occupation. My friend Kevin, he is a writer. 作者 is someone who writes the book, an author. Harry Porter的作者是J. K. Rowling .

作家 is the people who dose well in writing. 作者 is the writer of an aticle/essay/paper etc. Every body can be a 作者 if he/she writes something ,but you can't call him/her a 作家。