Updating ISO 1996-1: Standardizing on the Community Tolerance Level for evaluating long-term noise annoyance

The ISO 1996-1 standard, “Acoustics—Description, measurement and assessment of environmental noise, Part 1: Basic quantities and assessment procedures” provides, in part, methodologies used to evaluate long-term noise annoyance. Prior to 2016, this was done using a sigmoid fit to the Schultz curve where the day-night sound level (Ldn) was adjusted to account for the effects of sound characteristics on the percentage of highly annoyed. As part of the ongoing ISO 1996-1 revision, the ISO working group is considering focusing noise annoyance assessment on the Community Tolerance Level (CTL). This is a minor modification in that the new sigmoid curve is based on loudness, but it explicitly suggests that community-related parameters are important to annoyance. These approaches make it easier to compare different communities’ tolerance to noise using a single number descriptor. It will also discuss approaches other than CTL and where these may be appropriate. This paper will describe our consideration of this approach, the benefits of using CTL for standardized comparisons, level adjustments, and other sound sources and characteristics