Measuring functions – NTi Audio Digirator DR2 User Manual

Page 44

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Measuring Functions

44

A nontransparent signal is indicated by the “DATA CHANGED”
message. This means that the received bit pattern is different
to the expected bit pattern. This could be caused by any chang-
es in e.g. the gain setting or in the word length with added
dither.

Sampling frequency, synchronization and clock source

The sampling frequency is fixed to 48 kHz but can be syn-
chronized to an external reference with 48 kHz within ±100
ppm range. External-synchronization is very helpful for offline
tests. e.g. to record the transparency test signal on a record-
ing system and analyze as played back. Also the test may also
optionally be conducted using two DR2 units in different loca-
tions, with one acting as the signal source and the other as the
analyzer.

INTERNAL Synchronization

In this mode the DR2 acts as a clock master and the connected
device or system is synchronizing its clock to the DR2. Select
this mode if the device under test is unable to generate its own
clock, or if the device under test automatically synchronizes to
signals presented to its input.

SYNC INPUT (external synchronization)

In this mode the device under test is the clock master and the
DR2 synchronizes to this connected device by selecting clock
via “SYNC INPUT“. Synchronization is necessary to prevent
from losing samples through drop-outs or glitches.

With no valid clock applied to the SYNC input of the DR2, the
internal sampling frequency starts to drift and the external
synchronization aborts. With no Sync signal the DR2 switches
back to its internal clock generation and transmits the test sig-
nal derived from its internal clock. As soon as this transmitted
signal again reaches the SYNC input, the selector boxes for
IMPEDANCE and CLOCK source will appear again.

With a word clock or video signal
applied to the DR2, it automatical-
ly tries to synchronize after query-
ing for the termination impedance
choice. With a valid AES signal ap-
plied the user should determine
whether the DR2 should Sync
(slave mode) or continue to run
from the internal clock (Master
mode).

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