source is selected (and the clock is present), the ADC will detect it on the “Word In” BNC
connector on the rear panel.
For convenience, when the ADC has detected and synchronized to a valid clock source, internal or
external, a “Lock” light (labeled “WC” for word clock. will illuminate on the front panel of the unit.
In the case of an external clock source, this light indicates that the clock signal is being received
successfully. This light also indicates that a valid clock is present a the word clock output
connector.
b)
Word Clock Multiplier
The word clock multiplier is used to control the frequency of the ADC’s internally generated
sampling rate. This setting applies to internal clocks only. The x1 setting should be selected for
word clock rates of 44.1kHz and 48kHz. The x2 setting should be selected for word clock rates of
88.2kHz and 96kHz. The x4 setting should be selected for word clock rates of 176.4kHz and
192kHz.
c)
Word Clock Input Signal
The word clock input is used to drive the ADC’s sampling from an external clock source. The
input must receive a signal greater than 2.4Vp-p for proper operation. BLA recommends using a
low jitter clock source like the Micro Clock MK2. This input is not terminated internally, and does
not require an external termination.
Please see Section IV “Clocking the BLA A2D” for additional important information on clocking
converters.
d)
Word Clock Output Signal
The word clock output can be used to drive other devices in the studio for digital audio sample
rate synchronization. The output is 5Vp-p and has a 75 Ohm “source termination.”
Please see Section IV “Clocking the BLA A2D” for additional important information on clocking
converters.
IV.
Clocking the Sparrow MK II
Much confusion in the audio industry has resulted from different manufacturers implementing
and recommending different clocking standards and levels. Termination and voltage are the two
parameters that most often cause different units to be incompatible. High speed digital signals,
like clocks and digital audio, can cause cables and distribution systems to exhibit behaviors
which may seem strange and unintuitive to the audio engineer. These behaviors are commonly
termed “Transmission Line Effects.” While it is beyond the scope of this manual to thoroughly
cover transmission line theory, we can quickly give the competent user some rules of thumb that
we feel will consistently yield satisfactory results.
Termination is the single most commonly misunderstood concept. A good way to think of the
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