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This section seeks to clarify some potentially confusing issues to do with synchronization.


Sync sources, masters and slaves


A single Orpheus connected to a host computer supports a range of reference sync options:


Sync Source





System is sync'ed to Orpheus' local clock



System is sync'ed to external wordclock applied to Orpheus



System is sync'ed to external S/PDIF applied to Orpheus



System is sync'ed to external ADAT (ADAT input must be enabled)



Orpheus is slaved to system clock from host PC



System is sync'ed to Orpheus' 1394 clock (not recommended)



When multiple Orpheus units are connected to a single host, only one unit (or the host) can be master.  The remainder are slaves to the master's reference sync which is transmitted on the FireWire bus.


Thus every port of every Orpheus in the system must operate at a common sample rate.


An exception to this is when a sample rate converter (SRC) is configured in Orpheus' 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 Orpheus system.  But 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.  Orpheus allows for this; as described in the Output Setup tab section of the Orpheus Control Panel chapter.


'Master' in the table reflects the state of the unit's front panel ''Master' indicator. If the device's is providing the sample clock to the FireWire for the host (and any other Orpheus devices), the master indicator is lit.  If the device is receiving its sample clock from the bus, the indicator is not lit.  Note that if an Orpheus is being clocked from its wordclock or DI input, and thus is providing the clock via the FireWire to other interfaces, it is considered to be a master.



Wordclock output


As well as outputting a clock at the selected sample rate, Orpheus' wordclock output can be configured to produce a '256x clock' (a clock at 256x the selected sample rate, e.g. a 'superclock') or a 'base clock' (44.1kHz if the sample rate is a 44.1kHz multiple, or 48kHz if the sample rate is a 48kHz multiple)





It is not possible to change the sample rate in a Windows system whilst any of Orpheus' ports are in use in WDM mode. In this case it is necessary to disconnect the ports from the application before changing the sample rate.


In Mac OS X, the Audio MIDI Setup panel contains a drop control for selection of the desired Sync Source.  However, in versions to date, the names of the selectable Sync Sources may not exactly match those in the  Sync Source control within the Orpheus Control Panel applet.  For this reason, it is recommended that the Orpheus Control Panel applet be used for setting the desired Sync Source.


If an external sync source such as DI or wordclock is selected, but is either absent or at a different rate from Orpheus' selected sample rate, all audio is muted.  If the reference is later applied at the appropriate rate, audio is re-enabled.