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The OctoPre and wordclock - how to set up your digital system

Published: Fri August 13, 2004  News Feed

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.)

Focusrite OctoPre cables for connecting the optional A/D cards
 
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 S/PDIF use are available separately from Focusrite as follows:

  • S/PDIF: 9-pin male connector to 4x phono (RCA) female connector cable.
  • AES-EBU: 9-pin male connector to 4 x XLR male connector cable.

Note that these cables are NOT included in the price of the A/D options, since different formats require different cables.

ADAT lightpipe format
 
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.)
 
Setting up OctoPre as WORD CLOCK MASTER using ADAT lightpipe digital format.

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.

Setting up OctoPre as SLAVE TO AN EXTERNAL WORD CLOCK MASTER SOURCE using ADAT lightpipe digital format.

  • 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.

Setting up OctoPre as WORD CLOCK MASTER using AES format

  • 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.

Setting up OctoPre as SLAVE TO AN EXTERNAL WORD CLOCK MASTER SOURCE using AES digital format.

  • 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. 

Pin Configuration for AES 9-Pin D-type A/D-Option

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

Setting up OctoPre as WORD CLOCK MASTER using S/PDIF format

When using the S/PDIF option with the OctoPre, this is the easiest way is to set things up, because word clock is already embedded within the S/PDIF 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 S/PDIF 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 \"S/PDIF\"

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 S/PDIF signal. The pin out is shown below.

Setting up OctoPre to SLAVE TO AN EXTERNAL WORD CLOCK MASTER SOURCE using S/PDIF digital format.

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 S/PDIF 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 \"S/PDIF\"

Pin Configuration for S/PDIF 9-Pin D-type A/D-Option 

D-type pin number and wire colour

XLR 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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