Centauri Application Note 23 Centauri AES/EBU Clocking

Centauri Application Note 23
Centauri AES/EBU Clocking
1 General
Centauri is a professional audio device and therefore it supports different kinds of AES/EBU
clocking. Wrong configuration of AES/EBU clocking can cause audio failures as clicks or
short interruptions which are very often originated by drifting clocks.
This applicatiion note explains the different kinds of AES/EBU clocking supported by
Centauri. The influence of ADAT clocking via the optical Toslink input interface is not
considered.
With Centauri there are four different kinds of AES/EBU clocking scenarios:
• Internal clocking
• Clocking by digital audio input
• Clocking by sync. input
• AES/EBU transparent (just available with Centauri II and special audio interface)
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2 Pinlayout of Centauri AES/EBU interface
The Centauri AES/EBU interface is a female DB9 port with the following pin layout:
DB9 female (Centauri)
Digital Audio Input
5
9
1
Digital Audio Output
4
8
1
Digital Audio Sync Input
3
7
1
3 x XLR
Description
2 of XLR1 (female)
3 of XLR1 (female)
1 of XLR1 (female)
In +
In Ground
2 of XLR2 (male)
3 of XLR2 (male)
1 of XLR2 (male)
Out +
Out Ground
2 of XLR3 (female)
3 of XLR3 (female)
1 of XLR3 (female)
Sync In +
Sync In Ground
This pinlayout is also described in the Centauri interface manual which can be downloaded
via the link:
www.mayah.com/content/download/pdfs/manuals/centauri-interface_eng.pdf
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3 Kinds of AES/EBU clocking
3.1
Internal clocking
At internal clocking an internal Centauri word clock determines the used sample rate of the
Centauri AES/EBU output. The following sample rates can be selected:
• 32 kHz
• 44.1 kHz
• 48 kHz
• 88.2 kHz
• 96 kHz
Figure 1:
Note:
Internal clocking is the default value since it enables AES/EBU output without the need of an
clocking signal via the digital audio input port or the AES/EBU sync. input port. However, if
every audio device in a AES/EBU audio chain use an internal clock, it is very probable that
all the internal clocks are slightly different and therefore audio clicks can occur.
If internal clocking is used then the Centauri AES/EBU clock should be the master clock for
all other AES/EBU equipment behind.
3.2
Clocking by digital audio input
If digital audio input is selected as clocking source for AES/EBU output then the clock of
the audio signal of the AES/EBU input port or the Toslink audio input port determines the
sample rate of the AES/EBU output.
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Figure 2:
Note:
If digital audio input is selected as AES/EBU synchroniation source then a digital audio
input signal should be fed to Centauri.
3.3
Clocking by sync. input
If sync. input is selected as clocking source for AES/EBU output then the clock of the sync.
AES/EBU input port determines the sample rate of the AES/EBU output. Usually the
AES/EBU sync. input signal is an empty AES/EBU frame but any AES/EBU signal can be
used.
Figure 3:
Note:
If sync. input is selected as AES/EBU synchroniation source then a sync. input signal
should be fed to Centauri.
Note 2:
Clocking by sync. input is very similar to the clocking via digital input . However, it enables
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that all AES/EBU devices of one location use one clock source independently of the fed in
AES/EBU input signal. This prevents audio failures by different clocks.
3.4
AES/EBU transparent
If AES/EBU transparent is used as coding algorithm the clocking at the AES/EBU output
must be considered differenty to the clocking scenarios described above.
At AES/EBU transparent all the bits of one AES/EBU stream are transferred transparently
over the whole transmission line. However, since the clock cannot be derived from the
AES/EBU data stream, the Centauri’s on both side of the transmission line must use the
same AES/EBU clock and therefore ‘internal‘ clocking is impossible. Furthermore the
AES/EBU ‘sync in’ port can not be used since at AES/EBU tranparent the refering sample
rate converter for this port is switched off. Therefore sychronization source for AES/EBU
output clock must be set to ‘digital audio in’ .
Figure 4:
Note:
AES/EBU transparent is a special software plugin. Furthermore it is just available with
Centauri II (not Centauri I) with a special audio hardware.
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4 How to set
The configuration of the AES/EBU synchronsation output source can be done via the
following menu items.
4.1
Front panel of Centauri I
Menu item: <Setup/Digital Audio Out Sync>
4.2
Front panel of Centauri II
Menu item: <Setup/Audio Settings/Digital Audio Out Sync>
4.3
Windows Remote Control
The latest the Centauri Windows remote control can downloaded via the link
www.mayha.com/remote.
The synchronization source for the AES/EBU output can be set via the remote menu item
<Settings/Audio..>.
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