Multiple Frequency Shift Keying (MFSK) is a multi-frequency shift ke ying (FSK), in which, in contrast to classic frequency shift keying, not only two, but several frequencies are used for the transmission of the digital signals
. With multi-frequency shift keying, several signals can be modulated simultaneously or sequentially. The number of frequencies is calculated from the logarithm of 2 and can range from 2 to 64. The most commonly used is MFSK16. With multi-frequency keying, the ratio of the step rate (baud) to the data rate
(bit/s) is lower than with binary transmission. One of the best-known MFSK methods is the two-tone method, which is used in telephone technology for dialling telephone numbers. Here, two tones are assigned to each symbol of the multi-frequency alphabet.