the pro version uses two crystals of CrystekCCHD575 from the United States (corresponding to 44.1 and 48k and their frequency doubling). The jitter of the crystal oscillator manufacturer is 82 femtoseconds, which means that M2pro can claim to use femtosecond clocks. (Reference: The standard galactic clock for MSB top-level decoding is 77 femtoseconds).