User`s guide

User's Guide Fireface UC © RME

9.8 Clock Modes - Synchronization

In the digital world, all devices must be either Master (clock source) or Slave (clock receiver).

Whenever several devices are linked, there must always be a single master clock.

A digital system can only have one master! If the Fireface’s clock mode is set to 'Internal',

all other devices must be set to ‘Slave’.

The Fireface UC utilizes a very user-friendly, intelligent clock control, called AutoSync. In Auto-

Sync mode, the system constantly scans all digital inputs for a valid signal. If any valid signal is

found, the Fireface switches from the internal quartz (Clock Mode – Current Internal) to a clock

extracted from the input signal (Clock Mode – Current ADAT etc). The difference to a usual

slave mode is that whenever the clock reference fails, the system will automatically use its in-

ternal clock and operate in Master mode.

AutoSync guarantees that record and record-while-play will always work correctly. In certain

cases however, e.g. when the inputs and outputs of a DAT machine are connected directly to

the Fireface UC, AutoSync may cause feedback in the digital carrier, so synchronization breaks

down. Remedy: switch the Fireface clock mode to Master (Clock Source – Internal).

The Fireface UC's ADAT and SPDIF inputs operate simultaneously. Because there is no input

selector, the Fireface UC has to be told which one of the signals is the sync reference (a digital

device can only be clocked from a single source). The Clock Source selection is used to define

a preferred input for the automatic clock system. This input will stay active as long as a valid

signal is found.

To cope with some situations which may arise in studio practice, defining a sync reference is

essential. One example: An ADAT recorder is connected to the ADAT input (ADAT immediately

becomes the AutoSync source) and a CD player is connected to the SPDIF input. Try recording

a few samples from the CD and you will be disappointed - few CD players can be synchronized.

The samples will inevitably be corrupted, because the signal from the CD player is read with the

(wrong) clock from the ADAT i.e. out of sync. In this case, the Clock Source should be set tem-

porarily to SPDIF.

RME’s exclusive SyncCheck technology (first implemented in the Hammerfall) enables an easy

to use check and display of the current clock status. Input Status indicates whether there is a

valid signal (Lock, No Lock) for each input (Word Clock, ADAT, SPDIF and LTC), or if there is a

valid and synchronous signal (Sync). In the field Clock Mode the clock reference is shown (Cur-

rent…). See chapter 31.1.

Under WDM the Fireface will (has to) set the

sample rate. Therefore the error shown to the

right can occur. A stable signal with a sample

rate of 32 kHz is detected at the ADAT input

(Sync), but Windows audio had been set to

44100 Hz before. The red color of the text

label signals the error condition, and prompts

the user to set 32000 Hz manually as sample

rate. Under ASIO the audio software sets the

sample rate, so that such an error can not

happen. If the input sample rate is different

then there will be no Sync indication.

With RME’s AutoSync and SyncCheck, finally anyone can master this common source of error,

previously one of the most complex issues in the digital studio world.