Clock Sources (Speed References) - Steinberg Nuendo SyncStation Operation Manual

Clock sources (speed references)

Once the position is established, the next important factor
for synchronization is the speed of playback. Once two
devices start playing from the same position, they must
run at exactly the same speed in order to remain in sync.
With digital audio, the speed is determined by the audio
clock rate. With video, the speed is determined by the
video sync signal.
For proper synchronization, a master speed reference
must be used and all devices in the system must follow
that reference. As a clock generator and distributor, the
SyncStation can receive a master clock signal and gener-
ate outgoing clock signals for multiple audio devices.
Internal generator
The SyncStation can use its internal crystal-locked clock
generator as a master clock source for an entire system.
This generator may also use an external source as a refer-
ence for the clock speed.
Video black burst and tri-level sync
When working with external video devices, it is necessary
to reference the video frame rate for speed information. A
video black burst generator is used to control the speed of
each video device including VTRs, video workstations,
and even high-end computer video cards. That same
black burst signal can be used as a reference for the
SyncStation's clock generator.
A black burst signal can be fed into the Video Sync BNC
connector of the SyncStation in order to lock the audio
sample rate to the video frame rate. The SyncStation sup-
ports two types of video sync signals. Standard definition
video (SD PAL or NTSC) uses the traditional bi-level sync
signal (simply known as black burst) for frame rates up to
30fps. HD video requires the use of tri-level sync signals
in frame rates up to 60fps. The SyncStation supports both
bi-level and tri-level video sync for the most compatibility
in today's HD video world.
Care must be taken to ensure that the incoming
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video frame rate matches that of the Nuendo project.
The SyncStation has a video sync "thru" connection to
allow the chaining of multiple video devices together with
one video sync signal.
Word clock
The SyncStation can reference its internal clock to incom-
ing word clock signals received on the "W/C IN" BNC
connector. All standard sample rates are supported from
32kHz up to 192kHz.
The word clock input uses a multiplier system to achieve
the various sample rates. The internal system clock has
three basic rates: 32kHz, 44.1kHz, and 48kHz. Using four
multipliers (1x, 2x, 4x, and 256x), all other standard sam-
ple rates can be derived.
For example, to use a 96kHz word clock signal, set the
system clock to 48kHz and the reference multiplier to 2x
(2 x 48=96).
The SyncStation can reference the following clock rates:
• 32kHz (Typically this rate will not use any multipliers since
they would be non-standard sample rates.)
• 44.1kHz, 2x = 88.2kHz, 4x = 176.4kHz
• 48kHz, 2x = 96kHz, 4x = 192kHz
• 256x is used only for Digidesign hardware superclock signals.
12.3MHz (48kHz x 256) is not a standard audio sample rate.
This same multiplier system is also used for the Sync-
Station's word clock and AES (1x and 2x only) outputs.
AES Audio Clock
The SyncStation may also use an AES digital audio signal
as a clock reference. Each AES input (XLR and BNC) can
be used as a clock reference. The AES inputs also use a
multiplier to derive high-resolution sample rates.
SPDIF and Opto
The SPDIF and optical Toslink inputs may be used as a
clock reference in the same fashion as the AES inputs.
Video, LTC and MTC (using frame reference)
The SyncStation may use signals other than word clock as
clock references. A high-quality video sync signal can be a
good source for a clock reference.
In cases where a high-quality audio clock source or video
sync signal is not available, other references can be used
to derive an audio clock. LTC and MTC sources are not
optimal but will suffice if no other clock reference exists.
The SyncStation is able to generate audio clock based on
these frame references.
10
Introduction