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Introduction
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As the number of Platinum OctoPre owners continues
to grow rapidly, the boffins at Focusrite Towers have noticed an increase
in the number of technical support calls and emails. The vast majority of
these are not because of faulty units, but because of incorrect user set-up
of word clock. Here's a few pointers on how to use word clock correctly...
When using multiple pieces of digital audio equipment it is necessary to
make sure that their bit-streams are all in sync. In order to do this all
equipment needs to be synchronised to a common word clock system. Somewhere
in this system a word clock 'master' must be dictating the word clock for
the rest of the equipment, (the 'word clock slaves') to follow. Failure
to sync all pieces of digital equipment to a common word clock source will
result in audible clicks and glitches in programme material. (Note that
it IS possible to use more than one digital format within a single digital
system, so long as all formats are set to the same bit depth and sample
rate, and so long as each piece of equipment is set up to receive in the
correct format.)
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Focusrite OctoPre cables for connecting
the optional A/D cards
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Cables to connect the lightpipe-only
A/D option are, of course, standard lightpipe cables which can be purchased
from any pro audio retailer. Hence Focusrite do not offer an Focusrite lightpipe
cable option.
Cables to connect the 9-pin connector for AES and SPDIF
use are available separately from Focusrite as follows:
SPDIF:
9-pin male connector to 4x phono (RCA) female connector cable.
UK MSRP £25 excl. VAT
AES-EBU: 9-pin male
connector to 4 x XLR male connector cable.
UK MSRP £25 excl. VAT
Note that these cables are NOT included in the price of the A/D options,
since different formats require different cables.
Figure 1 (left): Focusrite's 9-pin AES cable (outside cable in the picture)
and 9-pin SPDIF cable (inside cable in the picture) |
ADAT lightpipe format
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Most ADAT-lightpipe-compatible equipment is 2-way
i.e. it outputs ADAT-format audio as well as being able to accept ADAT-format
audio input. This means that there are 2 options with regard to word clock
set-up and the OctoPre.
1) The OctoPre can be used as the word clock master.
2) The OctoPre can be slaved via a BNC word clock cable to run off an external
word clock source. (Where possible, when using external clocks, customers
should use a dedicated word clock master generator device from a reputable
manufacturer to supply the word clock to avoid the dangers of 'word clock
smear.' Failure to have a rock solid word clock source can cause word clock
problems (audible clicks etc as the word clock 'slips' from one cycle to
the next.) However, even if there is only slight word clock 'drift' (not
enough to cause 'clicks' etc) it can still definitely downgrade audio quality.
This loss of quality can easily be heard, even by an amateur listener!)
Note: Just plugging an ADAT cable from the Octopre to another piece of equipment
does not necessarily guarantee it will work! (See "Setting up OctoPre
to SLAVE TO AN EXTERNAL WORD CLOCK MASTER SOURCE using ADAT lightpipe digital
format" below.)
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Setting up OctoPre as WORD CLOCK MASTER using
ADAT lightpipe digital format.
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When using the ADAT option with the OctoPre,
this is the easiest way is to set things up, because word clock is already
embedded within the ADAT signal.
- Connect a lightpipe cable from either of the OctoPre's lightpipe ports.
(If using ADAT lightpipe format at 96kHz you will need to connect 2
lightpipes, one to each optical port. The first port transmits data
relating to channels 1-4, and the 2nd port transmits data relating to
channels 5-8.)
- Set the receiving device in your word clock chain (e.g. a soundcard
or digital mixer) to slave from the OctoPre's ADAT clock source. If
this equipment is not slaved correctly, word clock sync. will be lost
and the customer will experience problems.
- Check that all devices including the OctoPre have the same sample
rate e.g. 44.1kHz.
- Check that all devices including the OctoPre have the same bit depth
e.g. 16 bit.
- Choose the source of external word clock to be "ADAT." (Find
the relevant menu on the receiving device.) Most manufacturers call
this "ADAT slaving" or similar.
Note: With regard to digital workstations, you will always need to sync
the software to the word clock format of the audio interface being used,
using Audio Hardware and Driver set-up menus. These will normally appear
in a pull down menu once the driver that comes with the soundcard is
selected. NB this will NOT be set to "ADAT" but rather
to match the menu option that relates to the soundcard/ interface being
used.
Example: OctoPre (ext sync switch
out, no BNC cable connected) -> Soundcard
(set to 'sync to external ADAT') ->
DAW (set to 'sync to [name of soundcard / interface'])
- Set up the other devices in your signal chain to receive external
word clock, and set up the format to match whatever format is being
used to send to those devices
- DO NOT connect a word clock cable between the OctoPre and any external
equipment.
- Set the 'ext. sync' switch on the OctoPre board's rear panel to the
'out' position.
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Setting up OctoPre as SLAVE TO AN EXTERNAL WORD CLOCK MASTER SOURCE
using ADAT lightpipe digital format.
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- Connect a lightpipe cable from the OctoPre's lightpipe port. (If using
ADAT lightpipe format at 96kHz you will need to connect 2 lightpipes,
one to each optical port. The first port transmits data relating to
channels 1-4, and the 2nd port transmits data relating to channels 5-8.)
- Set one external unit to be the master clock source (usually called
'self generating' or 'internal' word clock.) Set all others, including
the OctoPre, to slave to a master clock source. All digital equipment
in the signal chain except the master clock needs to be set up as a
word clock slave. If any equipment is not slaved correctly, word clock
sync. will be lost and the customer will experience problems.
- Check that all devices including the OctoPre have the same sample
rate e.g. 44.1kHz.
- Check that all devices including the OctoPre have the same bit depth
e.g. 16 bit.
- Choose the source of external word clock to be ADAT. (Find the relevant
menu on the next receiving device. Most manufacturers call this "ADAT
slaving" or similar.)
- Connect a word clock cable between the OctoPre and the word clock
source.
- Set the OctoPre to also slave to the external master clock source
by pressing the 'ext. sync' switch on the OctoPre board's rear panel
to the 'in' position.
- If you have connected a lightpipe(s) the OctoPre will automatically
lock to external word clock once the BNC word clock cable is connected
and the ext. sync' switch is pressed in.
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Setting up OctoPre as WORD CLOCK MASTER using AES format
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When using the AES option with the OctoPre,
this is the easiest way is to set things up, because word clock is already
embedded within the AES signal.
- Connect Focusrite's AES cable option to the OctoPre's 9-pin D type
connector (feeds 4 x male XLR type connectors.) Connect the XLRs to
your AES destinations. If you are only using 2 channels, connect only
one XLR connectors that carries signal for the two OctoPre channels
you have chosen to connect. Each XLR connector carries two channels
of AES signal. The pin out is shown below.
- Set all external units to slave from the OctoPre's AES clock source.
All external digital equipment needs to be set up as a slave. If any
equipment is not slaved, word clock sync. will be lost and the customer
will experience problems.
- Choose the source of external word clock to be AES. (Find the relevant
menu on the next receiving device.)
- DO NOT connect a word clock cable between the OctoPre and any external
equipment.
- Set the OctoPre to be the master clock source by pressing the 'ext.
sync' switch on the OctoPre board's rear panel to the 'out' position.
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Setting up OctoPre as SLAVE TO AN EXTERNAL WORD CLOCK MASTER SOURCE
using AES digital format.
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- Connect Focusrite's AES cable option to the OctoPre's 9-pin D type
connector (feeds 4 x male XLR type connectors.)
- Set all external units to slave from the OctoPre's AES clock source.
All external digital equipment needs to be set up as a word clock slave.
If any equipment is not slaved, word clock will be lost and the customer
will hear nothing (except digital clicks and pops.)
- Choose the source of external word clock to be AES. (Find the relevant
menu on each piece of external equipment.)
- Connect a word clock cable between the OctoPre and the master word
clock source.
- Set the 'ext. sync' switch on the OctoPre board's rear panel to the
'in' position.
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Pin Configuration for AES 9-Pin D-type A/D-Option
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| D-type pin number and wire colour |
XLR pin number |
Audio channel and identification colour |
| 9 RED |
2 |
1+2 BLACK |
| 5 BLACK |
3 |
| Shell |
1 |
| 8 RED |
2 |
3+4 RED |
| 4 BLACK |
3 |
| Shell |
1 |
| 7 RED |
2 |
5+6 YELLOW |
| 3 BLACK |
3 |
| Shell |
1 |
| 6 RED |
2 |
7+8 BLUE |
| 2 BLACK |
3 |
| Shell |
1 |
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Setting up OctoPre as WORD CLOCK MASTER using SPDIF format
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When using the SPDIF option with the OctoPre,
this is the easiest way is to set things up, because word clock is already
embedded within the SPDIF signal.
The set up is exactly the same as setting up OctoPre to be word clock
master using the AES digital format, except that:
- The cable connection should be Focusrite's SPDIF cable option from FF, (9-pin
D type connector to 4 x female RCA/phono connectors.)
- The format of the external word clock should be set to "SPDIF"
If you are only using 2 channels, connect only one RCA/phone connector
that carries signal for the two OctoPre channels you have chosen to connect.
Each RCA/phone connector carries two channels of SPDIF signal. The pin
out is shown below. |
Setting up OctoPre to SLAVE TO AN EXTERNAL WORD CLOCK MASTER SOURCE
using SPDIF digital format.
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The set up is exactly the same as setting
up OctoPre to be word clock slave using the AES digital format, except
that:
- The cable connection should be Focusrite's SPDIF cable option from FF, (9-pin
D type connector to 4 x female RCA/phono connectors.)
- The format of the external word clock should be set to "SPDIF"
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Pin Configuration for SPDIF 9-Pin D-type A/D-Option
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| D-type pin number and wire colour |
Phono pin number |
Audio channel and identification colour |
| 9 RED |
Signal |
1+2 BLACK |
| 5 BLACK |
Ground |
| 8 RED |
Signal |
3+4 RED |
| 4 BLACK |
Ground |
| 7 RED |
Signal |
5+6 YELLOW |
| 3 BLACK |
Ground |
| 6 RED |
Signal |
7+8 BLUE |
| 2 BLACK |
Ground |
| 1 GREEN |
Shell Earth |
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