User manual

8X96 ADC and DAC User Manual Page 9 of 54
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8X96 ADC - Features
Sampling Frequencies and External Synchronization
The Analog-Digital converters are implemented as 4 stereo pairs. They operate
synchronously , i.e. all 4 converters always receive the same clock. As a result, all 8
digital outputs (or 4 stereo pairs of digital signals) are in sync and in phase.
The converters need a sampling clock of any frequency btwn. 25-100 kHz. If Analog
Input is selected, the A/D converters are active and can be clocked by the internal crystal
oscillator (set ADC SYNC =“Internal”) or external wordclock (set ADC SYNC =
“Wrdck.”).
The internal crystal oscillator provides 4 sampling frequencies:
-44.1 kHz (Set SAMPL=”44.1” and SAMPLING=”Reg(x1)”)
-48 kHz (Set SAMPL=”48” and SAMPLING=”Reg(x1)”)
-88.2 kHz (Set SAMPL=”44.1” and SAMPLING=”Hi-Sp(x2)”)
-96 kHz (Set SAMPL=”48” and SAMPLING=”Hi-Sp(x2)”)
The SAMPL and SAMPLING set the sampling frequency of the ADC only, but they
always have to be set properly as they are used to set the digital output sampling flags.
When digital input is selected the incoming sample rate is maintained throughout the unit.
The 8X96 ADC has a robust, very low jitter (<10ps) crystal oscillator for sampling
frequencies of 44.1, 48, 88.2 and 96kHz. For all tasks that don’t require slaving to an
external clock, the use of this internal clock is recommended as it achieves the lowest
possible jitter, resulting in maximum converter performance. It is recommended that
external devices such as DAW or recorders be slaved to the A/D. If the converter is
resolved to external wordclock, the clock jitter may increase depending on the stability of
the wordclock source. Incoming clock jitter is attenuated but not eliminated. Thus the
sampling clock quality is proportional to the quality of incoming wordclock. Therefore,
the use of the internal crystal generator is recommended for highest quality. If the
8X96ADC is used to feed a DAW, we recommend setting the DAW clock source to
“digital input” and setting the ADC to internal clock. This arrangement will provide the
best performance. If external clock source must be used (e.g. for video work), a stable
external wordclock generator is recommended. Proper 75 Ohm termination (set through
internal jumpers) can reduce wordclock jitter, especially for long cable runs. (Note: make
sure that the wordclock source is able to drive a 75 Ohm load).