Synchronization - Prism Sound Atlas Operation Manual

Prism Sound Atlas Operation Manual Revision 1.00
5.2

Synchronization

This section seeks to clarify some potentially confusing issues to do with synchronization. Note that
use of multiple Atlas units on a single host computer is not currently supported.
Sync sources, masters and slaves
Atlas behaves as a class compliant UAC2 (USB Audio Class 2.0) device, and operates in
asynchronous mode. This means that the sample clock is always controlled from within the Atlas unit,
and is NEVER locked to the USB bus or the host computer.
Where Atlas is generating its sample clock from its internal reference clock (local mode) it is
considered to be the clock master, and its front panel 'master' LED is lit. When it is locked to an
external sync source (Wordclock, DI or ADAT) it is considered to be a clock slave, and its front panel
'master' LED is not lit. Where an external sync source has been selected but is either invalid or is
operating at a different frequency from the nominated sample rate, the 'master' LED flashes and the
internal (local) reference is used instead. An exception to this is that during stand-alone operation, the
sample rate automatically follows the frequency of the selected sync source so long as it is valid. For
more information see the Unit settings and Stand-alone operation sections.
Every input and output channel must operate at a common sample rate and is locked to a common
synchronization source. An exception to this is when a sample rate converter (SRC) is configured in
Atlas's digital input or output. In the former case, the SRC simply converts any incoming digital signal
of whatever sample rate to the sample rate of the Atlas unit. If the SRC is in the digital output, it is
necessary to specify what the output sample rate must be; furthermore, it may be necessary to lock
the output rate to an arbitrary external reference. Atlas allows for this; as described in the Outputs tab
section of the Atlas Control Panel app chapter.
Wordclock output
As well as outputting a clock at the selected sample rate, Atlas's Wordclock output can be configured
to produce a '256x clock' (a clock at 256x the selected sample rate, e.g. a 'superclock') or a
'Baseclock' (44.1kHz if the sample rate is a 44.1kHz multiple, or 48kHz if the sample rate is a 48kHz
multiple).
TAKE NOTE
It may not be possible to change the sample rate whilst any of Atlas's ports are in use by an
audio application (e.g. a DAW). In this case it is necessary to disconnect the ports from the
application before changing the sample rate, or (where possible) to change the rate from
within the application.
If an external sync source such as DI or Wordclock is selected, but is either absent or at a
different rate from the selected sample rate, the unit reverts to local (internal) sync at the
selected sample rate. If the reference is later applied at the appropriate rate, audio is
re-enabled. Note that during Stand-alone operation an external sync source is allowed to
control the unit's sample rate.
© 2014 Prism Media Products Ltd 1.29