I'm sure that the OP has already visited, so I'm posting this for future readers of this thread. The hotels next to the convention center are in what I would consider a quiet area. I enjoyed my stay at the Hilton Bayfront and when I went outside to walk along the bay it was quiet. If you go across the ped bridge into the heart of the Gaslamp, you'll encounter a much nosier environment.
Another quiet area that I like is the around the Sheraton Marina. I've stayed at that Sheraton several times and it's a peaceful area. Walking along the bay in that area with a cup of coffee in the morning is so relaxing. There's typically people running and walking. There is also a path that you can walk that takes you from the hotel, along the marina, and under the N Habor Dr bridge to another quiet are where there is Starbucks, a park and a walking trail around the water in that area. It's a short drive from Balboa Park and the zoo from the hotel.
Someone mention La Jolla and while I absolutely love walking along the cove, Prospect st, Girard Ave, dining outside at George's on the Cove, dining outside at The Med and happy hour at Catania, it's not the most quiet area, specifically along Prospect St where most of the nice hotel are.