Multiple frequency-shift keying (MFSK) is a variation of frequency-shift keying (FSK) that uses more than two frequencies. MFSK is a form of M-ary orthogonal modulation, where each symbol consists of one element from an alphabet of orthogonal waveforms. M, the size of the alphabet, is usually a power of two so that each symbol represents log2M bits.
{play}http://www.pa4rm.com/attachments/069_mfsk-8.mp3{/play} MFSK-8 test sample
{play}http://www.pa4rm.com/attachments/069_mfsk-16.mp3{/play} MFSK-16 test sample