CTCSS (Continuous Tone Coded Squelch System) a.k.a: Private Line (PL), Channel Guard (CG), and tone squelch. CTCSS and tone squelch are the generic terms for Motorola's PL or GE's CG.
Just as the name above implies, CTCSS is a continuous tone that is so low in frequency and amplitude (volume) that it is almost impossible for a human to hear with an un-aided ear. This subaudible tone is sent over the air with a tone encoder to the receiving station which, in turn, has a tone decoder. The decoder doesn't let any sound through to the speaker until it hears the specific tone it was programmed to listen for. This allows users to be on one frequency without causing interference to more distant stations using different subaudible tones.
CDCSS, also called DCS, is a digital subaudible selective signalling system. It does the same thing as CTCSS, but in a different way.
It uses a code composed of 23 bits sent repeatedly at rate of 134.3 bits per second. The code is based on the Golay (23,12) code first published in 1949. This code has the ability to detect and correct any three bit or less error that occurs in the 23 bit word.
CTCSS, AFAIK does not have any error correction.
It is a filter ... so if it is on, its gonna filter.
