Assembly: Microsoft.Speech (in microsoft.speech.dll)
The DtmfRecognitionEngine class supports the use of speech-type grammars to analyze DTMF input. Its API is like that of SpeechRecognitionEngine, but its recognition input is a series of DTMF tones instead of an audio stream.
DtmfRecognitionEngine works by performing a series of emulated recognitions. It maintains a buffer with a list of tones that have been received. Every time a new tone is received, it appends the new tone to the list and emulates recognition of the whole list. This process continues until emulation produces a definitive result, or one of the timeouts is reached.