CTCSS is an acronym for Continuous Tone-Coded Squelch System and is a system that is used in shared two way radio systems. It is common for a single radio channel to be shared over a number of user groups for frequency use efficiency. CTCSS uses a special tone to identify each group of users, and this tone is used to prevent a group hearing radio chatter from another group sharing the channel.
A new digital noise reduction plugin for SDRSharp has been released. It is packaged as part of the SDRSharp binaries. Head to the SDRSharp downloads page, and download and use the automated installer for rtl-sdr under the heading “Important note for RTL-SDR users”.
Then in SDRSharp, simply click “Enabled” in the Digital Noise Reduction plugin window and adjust the slider until you get good results. In testing I found significant improvements in noise reduction.