Couch potatoes of America, listen up. Congress may be just days away from turning down the volume on ear-splitting TV.

The Commercial Advertising Loudness Mitigation, or CALM, Act follows rules set last year by a United Nations body in Switzerland on how to measure and clip broadcast volumes. The U.S. bill, inspired by decades of consumer complaints, should finally ban TV ads that blare louder than the programs they interrupt.

California...