RME Audio OctaMic XTC, Руководство пользователя

Страница: 51 / 62

User’s Guide OctaMic XTC
© RME
51
22.2 Lock and SyncCheck
Digital signals consist of a carrier and the data. If a digital signal is applied to an input, the re-
ceiver has to synchronize to the carrier clock in order to read the data correctly. To achieve this,
the receiver uses a PLL (Phase Locked Loop). As soon as the receiver meets the exact fre-
quency of the incoming signal, it is locked. This
Lock state remains even with small changes of
the frequency, because the PLL tracks the receiver's frequency.
If an AES or MADI signal is applied to the OctaMic XTC, the corresponding LED starts flashing.
The unit indicates LOCK, i. e. a valid input signal (in case the signal is in sync, the LED is con-
stantly lit, see below).
Unfortunately, LOCK does not necessarily mean that the received signal is correct with respect
to the clock which processes the read out of the embedded data. Example [1]: The OctaMic
XTC is set to 44.1 kHz internal clock (clock mode master), and a mixing desk with MADI output
is connected to the XTC MADI input. The MADI LED will start flashing immediately, because the
mixing desk's sample rate is generated internally, and thus slightly higher or lower than the
XTC's internal sample rate. Result: When reading out the data, there will frequently be read
errors that cause clicks and drop outs.
Also when using multiple inputs, a simple LOCK is not sufficient. The above described problem
can be solved elegantly by setting the OctaMic XTC from internal clock to MADI In (its internal
clock will then be the clock delivered by the mixing desk). But in case another asynchronous
device is connected, there will again be a slight difference in the sample rate, and therefore
clicks and drop outs.
In order to display those problems optically at the device, the OctaMic XTC includes
Sync-
Check . It checks all clocks used for synchronicity . If they are not synchronous to each other (i.
e. absolutely identical), the LED of the asynchronous input flashes. In case they are synchro-
nous the LED stays dark, only the LED of the current clock source will be lit (constantly). In
example 1 it would have been obvious that the STATE MADI LED keeps flashing after connect-
ing the mixing desk.
In practice, SyncCheck allows for a quick overview of the correct configuration of all digital de-
vices. This way one of the most difficult and error-prone topics of the digital studio world finally
becomes easy to handle.