Frequency recognition is an important task in many engineering fields, such as audio signal processing and telecommunications engineering. This work investigates four of the frequency recognition algorithms implemented in real time. The key idea is to adapt to the well-proven frequency recognition algorithms of DTMF systems, which are successfully and widely used in telephony. The investigations will show to what extent these principles and algorithms can be applied. Implementation of the frequency recognition algorithms on a Texas Instruments (TI) TMS320C6713DSK Digital Signal Processor (DSP) core, in order to estimate the frequency of DTMF digits in real time, is also presented.