# Making Hardware Clock Connections

Symphony I/O provides several facilities for the connection of clock signals:

- Word Clock inputs and outputs - Use the word clock inputs and outputs for most clock connections to digital consoles, digital effects devices, or other digital audio devices equipped with standard word clock I/O.

- Loop Clock inputs and outputs - Use Loop clock inputs and outputs to lock together multiple Symphony I/Os in a computer-based digital audio workstation (DAW) such as Apogee's Symphony 64 PCI system. Symphony I/O's Loop clock is compatible with Avid Pro Tools Loop Sync, meaning that a Symphony I/O may be freely incorporated into a Pro Tools HD system Loop Sync chain.

- Digital audio inputs and outputs - Use Symphony I/O's digital audio I/O to send and receive clock between Sympony I/O and digital devices that don't include work clock I/O. When using Symphony I/O in Standalone audio interface mode, the most convenient way to clock the connected digital device is through the digital audio input from Symphony I/O.

In Symphony and Pro Tools HD audio interface modes both loop and "star" clock configurations are possible, as described below.

## Locking external devices to a single Symphony I/O

To lock external clock devices to a single Symphony I/O:

> 1. Connect the rear panel WC OUT to the word clock input of the device, using a BNC cable as shown below. Set the external device's clock source to Word Clock.
> 2. When connecting digital devices to Symphony I/O’s AES, ADAT/SMUX or S/PDIF outputs, clock is transmitted with the digital connection, allowing the receiving device to simply clock to its digital input.

## Locking a single Symphony I/O to external devices

To lock a single Symphony I/O to external devices such as a Master clock:

> 1. Connect a BNC cable between the device's word clock output and Symphony I/O’s WC IN, as shown below. When using multiple interfaces, connect to the master Symphony I/O's WC IN. Note that lock to external clocks isn't supported in USB audio interface mode.

> 2. If no other devices are to be connected, press in the rear panel termination (WC Term) switch.

> 3. To lock Symphony I/O to a digital input, connect the source's digital output to Symphony I/O digital input.

> Once clock connections are made, see Setting the Clock Source to complete the process. Note that software settings may vary based on the audio interface mode.

## Locking multiple Symphony I/Os together with Loop Clock

When multiple Symphony I/Os are used together in a digital audio system (for example with a Symphony 64 or Avid Pro Tools HD PCI card), use the rear panel Loop connections to lock the Symphony I/Os together, as described below. With a Pro Tools HD system, Symphony I/O Loop Sync connections are compatible with all Avid interface equipped with Loop Sync connections.

Using a BNC cable, connect the Loop Out of unit 1 to the Loop In of unit 2. With additional BNC cables, connect the Loop Out of each unit to the Loop In of the next unit until all units are connected. Finally, connect the Loop Out of the last unit to the Loop In of the first unit. Please consult the diagram below for an example connection.

## Locking multiple Symphony I/Os to external devices (Loop clock configuration)

To lock multiple Symphony I/Os to external devices such as a master clock, first connect Loop Clock as shown above. Then connect a BNC cable between the device's word clock output and one Symphony I/O’s WC In. Configure this Symphony I/O as the Loop Master as described in Setting the Clock Source.

## Locking multiple interfaces using a "star" clock configuration

When a direct clock connection is made between all devices and a single master clock (such as Apogee's Big Ben Master Clock), this is commonly designated as a "star" clock configuration, as depicted below:

A star clock configuration may be the most robust configuration possible, as there's only one clock cable between each device and the clock master. This reduces the possibility that connection issues may arise resulting in mis-clocking or loss of clock altogether. On the other hand, star configurations are less flexible with multi-interface DAW systems, and may be trickier to implement. Symphony I/Os may be configured using either a star configuration or loop sync configuration with Symphony 64, Mobile and ThunderBridge systems or Pro Tools HD systems.

In most cases the user may choose between a loop sync and a star configuration, but under these circumstances a star configuration is required:

> When using a mix of Symphony I/Os, 16X and Rosetta series interfaces connected to a Symphony 64, Mobile or Thunderbridge system.

> When using a mix of Symphony I/Os, 16X series, Rosetta series and Avid interfaces connected to a Pro Tools HD system.

> When direct lock to a master clock is considered a requirement.

In a true star configuration, the master clock is often locked to its internal crystal or to a video clock source, and thus sets the sample rate for the entire system. This poses a potential pitfall with DAW systems, in that the master clock's sample rate may become mismatched from the software sessions's sample rate. To avoid the possibility of a mismatch, it's recommended that one interface connected to the DAW be set to Internal and that the master clock be locked to that interface. Next, all remaining interfaces are locked directly to the master clock. This configuration is shown below.

For the case of a Pro Tools HD rig that includes a Sync I/O, the following configuration is suggested. With this configuration, the Sync I/O's clock source functionality is retained while each interface has a direct connection to the master clock.