Is the baby mobile, is it crawling around, maybe going up to the dog when it is sitting or laying down?
Before your little one came along had the dog had any interaction with children especially ones of this age, I would bet my last dollar that he didnt, because no matter how well we socialise our dogs they cannot meet everyone of every age in every situation no matter how how we try.
Before the human baby came along I would hazard a guess your Dobe was your baby. Pampered, set upon a bit of a pedastal. We all do it and even though we can try and convince ourselves our relationship with our dogs has not changed in the slightest since baby came along, we also know that is just not true. And guess who knows this more than you, yep your Dobe. Now I am not saying he is jealous, but I would be surprised if he wasnt a little put out at times by baby and how you react to him. Add to this if the baby is crawling around, wriggling, shuffling, whatever your baby is doing the fact is, it is invading his space even more.
By his growling showing his teeth at your baby doesnt in my opinion indicate your boy is vicious or aggresive, if he was you would be posting 'help my dobe just savaged my baby' it just means he is being a dog
My advice would be to keep the baby away from the dog. He is trying to tell the little one he doesnt like what ever it is he is doing, but being a baby he hasnt the ability to understand what is going on. It is up to you to understand for him, for them both.
If you can, take your Dobe along to the vet to rule out anything physical that is causing him to be grumpy. Then if you can bring in a behaviourist to advise you how to proceed. But most of all, just try to keep the baby and Dobe apart without the Dobe feeling he is being pushed out all the more and train your baby to stay away from the dog. (this advice is applicable to any dog not just our Dobe babies).