US law says TV adverts to play at same volume as show
The US has implemented a law to limit the volume of TV adverts, to play at the same level as the main programme.
The Commercial Advertisement Loudness Mitigation (Calm) Act applies to broadcasters, and cable and satellite companies.
Previously, adverts could play at a higher volume level than the programme.
The rules were taken up by the Federal Communications Commission (FCC) a year ago but the industry had a one-year grace period to prepare for them.
Correspondents say the rules are meant to protect viewers from excessively loud adverts, which can seem intrusive.
The FCC suggests that enforcement of the new rules will be driven by complaints, and viewers can report suspected violations of the rules on their website.
The Calm Act applies only to TV adverts, and not radio programmes or shows on the internet.
The bill was sponsored by California congresswoman Anna Eshoo, who told the Wall Street Journal in 2010 that it was one of the most popular pieces of legislation she had introduced in her 18 years in Congress.
"If I'd saved 50 million children from some malady, people would not have the interest that they have in this," Ms Eshoo told the newspaper at the time.
Championed by Senator Roger Wicker of Mississippi, it was approved unanimously in the upper chamber.
President Barack Obama signed the legislation into law on 15 December 2010.