I'm a Speech-Language Pathologist who has specialized in early childhood communication development for 15 years. I have some resources about language development in general and the specific concern you are describing.
The American Speech-Language Hearing Association (ASHA) has a nice page of links to answer parents' questions about normal communication development. These links will hopefully answer most questions you have about typical language development.
As for your specific situation, you describe that your son does not respond to his name when people call him. This is a warning sign for language development. The first thing to do is to rule out hearing as a factor in this pattern of development. The next thing to do, if hearing is fine (which you can't know completely by the fact that he responds to music) is to have an appointment with a Speech-Language Pathologist. At 2 years of age there is an extremely wide range of how many words a child can be using and be considered typical. Some children are speaking in complete sentences, others are not. The things I find to be more important are:
Can your child pay attention to people who are talking to him and
understand and follow some instructions? This is very important.
Children should be understanding a wide variety of words, in whatever
language they are growing up hearing, by age 2.
Can your child express basic wants and needs with a combination of
gestures, words or word attempts, and eye contact with an adult (if
this is culturally appropriate), or do adults have to figure out what
the child wants on their own?
Is your child making a lot of noises that sound like talking but
aren't recognizable as words? A "silent child" is also a warning
I often find that children's doctors don't know what is typical and what is not for communication development. Children will also not act the way they usually do when they are at the doctor's office, so evaluating a child's development by observing them for 10 minutes during a checkup is not helpful.
Hopefully the links from ASHA will provide some useful information.