User Manual

User's Guide ADI-4 DD © RME

8. Clock Section

8.1 Clock Configuration

The ADI-4 DD has a common clock section for both converters, with professional capabilities

that are hard to meet. The unique ICC technology (Intelligent Clock Control) offers professional

features with simplest usage. All options are easily applicable and understandable, thanks to a

clear display of the corresponding lock state.

As SYNC source, WC (Wordclock), ADAT (IN 1 / IN 2) and AES (AES 1: XLR, Sub-D, IN 2) can

be chosen. If the clock signal is present, the corresponding LED will light constantly. If not, then

the LED will flash. The clock choice is independent from the processed audio signal and con-

version mode.

The ADI-4 DD has no internal clock, therefore can't be master. Being slave it has to be fed

with a reference clock from an external master.

8.2 Lock, SyncCheck and SyncAlign

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 ADAT signal is applied to the ADI-4 DD, the corresponding input LED begins to

flash. The ADI-4 DD indicates LOCK, i. e. a valid input signal.

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 ADI-4 DD is

synced to 44.1 kHz of a CD-Player connected to input AES1. The corresponding input LED will

be lit. Now when connecting a second, not synchronized DAT machine to AES2, there will be a

slight difference in the sample rate, and therefore clicks and drop outs. Another example could

be connecting two ADAT machines which are not synchronous to each other due to wrong

clock setup.

In order to display those problems optically at the device, the ADI-4 DD features SyncCheck

It checks all clocks used for synchronicity. If they are not synchronous to each other (i. e. abso-

lutely identical), the SYNC LED of the asynchronous input flashes. In example 1 it would have

been obvious at once that the AES1 LED was constantly lit when connecting the CD-Player, but

the SYNC LED of AES2 was flashing. In example 2, again one of both ADAT SYNC LEDs

would be flashing.

In practice, SyncCheck allows for a quick overview of the correct configuration of all digital de-

vices. So one of the most difficult and error-prone topics of the digital studio world finally be-

comes easy to handle.

A special problem occurs with devices offering several AES or SPDIF inputs. While with ADAT

and TDIF all 8 channels share the same clock base, with AES there are several completely

independent receivers with their own PLLs and data buffers. Therefore there can be a random

error of ± 1 sample difference between the stereo pairs. The ADI-4 DD's exclusive SyncAlign

technology avoids this effect and guarantees sample synchronicity among all 4 stereo channels.