Open main menu Home Random Nearby Log in Settings Donate About Wikipedia Disclaimers Search Article Talk Language Watch Edit version 1.0.2 (change every time you update a partial) In telecommunications , Continuous Tone-Coded Squelch System or CTCSS is one type of in-band signaling that is used to reduce the annoyance of listening to other users on a shared two-way radio communications channel. (See squelch .) It is sometimes referred to as tone squelch. It does this by adding a low frequency audio tone to the voice. Where more than one group of users is on the same radio frequency (called co-channel users ), CTCSS circuitry mutes those users who are using a different CTCSS tone or no CTCSS. It is sometimes referred to as a sub-channel , but this is a misnomer because no additional channels ar...