Noisy TV commercials have been banned in California, with a new law that demands pitchmen turn the volume down.

Viewers in the United States have long complained that advertisements can be much louder than the program they are streaming.

One minute they are engrossed in a peaceful nature documentary and the next they are scrabbling for the remote to quieten a man shouting about a new treatment for his flatulence.

Now a new law in America's most populous state says commercials cannot be any louder than the content they interrupt.

"We heard Californians loud and clear, and what's clear is that they don't want commercials at a volume any louder than the level at which they were previously enjoying a program," governor Gavin Newsom said after signing the bill into law on Monday.

The legislation rewrites outdated laws that only regulated broadcast and cable providers to now include streamers. (AFP)