External AES Clock Sync and Livewire Clock

[Bruce Wilkinson]

Livewire runs on a 48kHz clock that is distributed to the Livewire devices using a very unique and robust syncing technique. There may be cases, however, where customers want to sync their Livewire system to an external AES clock.

Here is a step-by-step guide to syncing your Livewire network's clock to an external AES source. The node config settings are in red italics like this.

While it is possible to use an external AES signal as a clock reference for your entire Livewire network. There are a few caveats:
- the AES reference must be VERY, VERY accurate. It must meet AES class A specification with <= 1PPM tolerance.
- the AES clock source must always be available
- the AES clock source must be 48k, not 44.1 or some other sample rate

When considering Clock Priority, in this configuration, one node will always be designated as a MASTER node for clock priority (Node 1 in this example) and all other nodes (Slaves) will be set at clock priority 3 (default). The Node designated as MASTER (Node 1 in this example) is your dedicated master and you will be feeding your AES clock source to one of its inputs. Configure it to be always master:

Livewire clock master priority: 7 (always master)

Our AES clock source is connected to e.g. input one:

AES sync source: IN 1

AES output sync. Both settings should work, but the operation will be a little bit different. If you set "AES output sync: AES sync source", the clock from selected "AES sync source" (in our example IN 1) will be immediately "wired" to AES output chips. You will get immediate sync of the AES outputs to selected input. This configuration will work on wider range of AES clock frequencies and tolerate more jitter but it is limited to sync within one node.

In order to sync more than one node to your source, you need "AES output sync: Livewire". We are trying to synchronize Livewire clock to AES source in IN 1 in this example. Once the Livewire clock properly follows that AES input, our outputs will be in sync as a result. We use the same setting on nodes that are the Slave nodes so for all AES nodes:

AES output sync: Livewire

Now, to tell the node to synchronize Livewire clock to AES IN 1, we set:

AES sync source as Livewire master timebase: yes

At this point, let's make sure that Master LED in the Node 1 is ON. Also the SYNC LED on node 1 should initially blink, but become solid ON as sync to AES IN 1 is achieved. This is a special case where a node is both MASTER and SLAVE.

On our Slave nodes the settings are below:

Livewire clock master priority: 3 (default)

AES sync source: Livewire 48kHz

AES output sync: Livewire 48kHz

AES sync source as Livewire master timebase: no

Once the Slave nodes are configured, the SLAVE LED should illuminate and stay on solid. If it blinks at all, we have a problem. Note that it may take a few minutes for the non-master nodes to "sync-up" but they should do so if your reference is accurate and your configurations are correct as outlined above.

Once the system has been configured as above, you can distribute AES signals in perfect sync.