a walkie - talkie device applies a continuous tone - coded squelch system to control signal transmission . the walkie - talkie device has an analog - to - digital converter , a digital signal processor , and a digital - to - analog converter . the signal processing method includes using the analog - to - digital converter to convert a first analog signal into a first digital signal , using the digital signal processor to handle a ctcss tone related to the first digital signal for generating a second digital signal , and using the digital - to - analog converter to convert the second digital signal into a second analog signal . the walkie - talkie device uses the ctcss tone to discriminate a required speech signal from other speech signals transmitted by the same physical channel .