How many decibels is the controllable noise reduction of 20-level ambient sound equivalent to?

24.4 decibels. According to China Environmental Protection Network. Article 2 of the Law of People's Republic of China (PRC) on the Prevention and Control of Environmental Noise Pollution states that the noise level is 20 to 40 decibels, as quiet as a whisper. The 20-level ambient sound controllable noise reduction belongs to the first-level noise reduction, and the decibel value of the first-level noise reduction is between 20 and 40. Therefore, the controllable noise reduction of 20-level ambient sound is equivalent to 24.4db.