Setting up your Octopre in a digital audio system.

A Guide to Setting Up Your Digital System



Introduction


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.)



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 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


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 SPDIF format


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.


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"


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


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