RME OCTAMIC XTC [51/62] Lock and synccheck

User’s Guide OctaMic XTC © RME

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.