DS has never really been a babbler. He is just not really bothered about vocalising very much. If you start him off with bababa dadada he will join in and add a few more sounds, but nothing approaching a word yet. Even dadada is general, not specific to daddy. He just seems happy being quiet if you don't push him.
He mixes well with other children on a regular basis and we talk to him all day long. He understands lots, he reacts to sounds, he points out objects, he follows commands very well. Just not a talker.
I'm not worried (yet), but I do feel the need for some reassurance. Its all fine at this age isn't it?