The microphone is a special input device that converts spoken words into computer understandable code and vice versa. This device converts data from the computer to the spoken words or sentences as well. Speech is digitised first then matched against the dictionary of coded waveforms, and finally matches are converted into text.
The microphone works in tandem with a sound card. You can speak your words or input a sound using microphone. In some speaker dependent systems, you need to enunciate samples into the system in order to tune it to your individual voice. The sound card translates the electrical signal from microphone into a digitised form that the computer can store and process. Microphones are useful because such systems have replaced human operators for telephone services. They also provide help to convert the typed text into speech and broadcast it over the speakers.