Measurements carried out by the German Aerospace Centre (DLR) at seven monitoring stations operated by Fraport and the Environment and Community Centre (UNH) showed a clear reduction in the maximum sound level ranging between 0.5 and 1.5 dB (A) depending on the monitoring station and the aircraft type. The measurements were conducted over the entire period of the trial operations.
Between October 2012 and December 2014, about 145,000 aircraft landed on runway northwest using the increased glide angle, representing 71 percent of all landings. During this time, the new procedure neither caused a higher number of go-arounds nor any delays for arriving aircraft.
The additional instrument landing system (ILS) and the required relocation of the glide path transmitter cost EUR 3.2 million. The operating costs amount to EUR 300,000 per year.
Not certain a 'clear' reduction of 0.5 to 1.5 is even perceptible to humans, and a significant cost...
a correlation was not done with the new aircraft coming on line in the 2 year timeframe, many of which are much quieter...
https://www.dfs.de/dfs_homepage/en/P...%20protection/
EDIT: I understand the 3.2 is an option for Gatwick?