Это мануал на девайс
http://www.m2tech.biz/public/pdf/hiFace Evo user manual 1-0.pdf
вот что там написано про внешнюю синхронизацию
Using the external clock
When a very high precision and stability clock source is available, an external clock can be
applied to hiFace Evo on the related BNC input (Figure 1, 2). Whenever the clock is
present with the right voltage, the LED indicator (Figure 1, 7) will lit in green and the
hiFace Evo will automatically revert to the external clock.
Of course, the automatic clock switching to accommodate both 44.1kHz-based and 48kHzbased
sampling frequencies will be disabled, as the interface will be clocked with the
external clock. So, clock switching must be performed at the clock source. Otherwise, only
one base sampling frequency files should be chosen for playback.
For example, if a 24.576MHz external clock is applied, 48kHz, 96kHz and 192kHz files will
be played back with the right pitch, while 44.1kHz, 88.2kHz and 176.4kHz files will have a
higher pitch than normal and will sound hurried-up.
Conversely, when using a 22.5792MHz external clock, 44.1kHz, 88.2kHz and 176.4kHz
files will be played back with the right pitch, while 48kHz, 96kHz and 192kHz files will have
a lower pitch than normal and will sound slowed down.
The external clock can also be used to play files with a base frequency different than those
available internally. For example, a 32kHz file can be correctly played back using a
16.384MHz external clock.
Вот еще некоторая информация про девайс
http://www.m2tech.biz/public/pdf/White Paper on hiFace.pdf
hiFace uses, in place of a PLL, two highest stability, very low phase noise crystal
oscillators. In standard environmental conditions, the precision is around 2,5ppm: this
means that they derive no more than 2,5Hz for every MHz of their output frequency. The
maximum error at 192kHz will thus be 0,5Hz! On the contrary, a PLL’s error can be up to
2-5%: this means that at 192kHz a change of nearly 10kHz is not uncommon. We think
we’re listening to the right sampling frequency, but actually we listen to a different
sampling frequency and all instruments are “out of tune”. Another problem with PLL’s is
the phase noise. It is the main responsible for jitter. The oscillators used in hiFace have
incredible performances on phase noise: -78dBc at 10Hz and as low as -140dBc at 1kHz.
Thus, the signal S/PDIF out of hiFace suffers of almost no jitter, also thanks to the use of
a high performance S/PDIF transmitter, the Burr-Brown/Texas DIT4192.
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