Distance from the Generator
One way to keep the noise level down is to place the generator as far as possible from other people. For instance, if you need to use your generator in a campground, try to find a campsite that doesn't have any close neighbors.
The GeneratorNoise.com website reports that a barrier wall can be effective in noise level reduction. But to do any good, the wall has to at least block the line of vision from the person to the generator. The wall also needs to be of solid construction with no holes in it.
Since generator noise is a known problem, manufacturers provide a noise level rating for their units, and they have made an effort to produce quieter units. However, GeneratorNoise.com reports that the companies don't always include the exhaust noise in their data. So if you are interested in buying a new generator for a recreational vehicle, check with the company about what its noise level information includes.
An important concept to understand about noise levels is that an increase of 3 decibels, or db, means that the sound is twice as powerful. For example, the sound coming out of a generator at 53 db is twice as strong as at 50 db.