What term describes the use of a sub-audible tone transmitted along with normal voice audio to open the squelch of a receiver?

The term that describes the use of a sub-audible tone transmitted along with normal voice audio to open the squelch of a receiver is CTCSS, which stands for Continuous Tone-Coded Squelch System. CTCSS allows for multiple conversations to occur on the same frequency without interfering with each other. By sending a specific tone along with voice audio, only receivers configured to recognize that specific tone will open their squelch and allow the audio to pass through. This feature is particularly useful in communication systems to minimize unwanted noise and ensure that users only hear relevant transmissions.

The other terms, while related to audio and squelch, refer to different concepts. Carrier squelch is a basic method that utilizes the presence of a carrier signal to control the squelch circuit but does not use a sub-audible tone. A tone burst generally refers to a short transmission of a tone used for identification purposes. DTMF (Dual-Tone Multi-Frequency), commonly known as touch-tone dialing, involves sending specific frequencies for dialing but is not used for squelch control in the way CTCSS operates.