Synchronizing to AES/EBU

Connections: Synchronizing the CobraNet Network to an AES/EBU Stream

The RAVE “s” series AES/EBU input models provide some additional means for synchronizing the CobraNet network and deriving on-board clocks. In addition to the on-board PLL and external synch inputs available on all models, the AES/EBU input models allow the user to synchronize the network to a 48 kHz AES/EBU input stream. The 48 kHz stream can be used in a similar manner to the external synchronization feature where a clock is applied to the rear panel “synch input” BNC connector. However, instead of applying an external clock to the rear panel, the RAVE recovers the clock from the AES input stream off the first XLR connector. The 48 kHz recovered clock can then be multiplied to acquire the 12.288 MHz master clock, which is needed for all local audio clocks.

Two methods of synchronization from an AES input stream are supported via jumper selections at J37 and J39. The 3-pin headers for jumpers J37 and J39 are available on the RAVE 81s and 88s models only, as the AES receiver at channel input number 1 is required.

Method 1: Synchronize to the AES input “master clock”. When the jumper on header J39 is set to “AES clock”, the CobraNet interface will disable the RAVE’s on-board PLL and instead use the 12.288 MHz clock recovered from the AES receiver at input number 1. Note that AES receivers are only available on the RAVE 81s and 88s products. Header J39 is located near the front of the RAVE PCB about midway between the status and metering LEDs. The jumper position for implementing synchronization to the AES “master clock” is shown below.

As with all synchronization methods implemented via hardware configuration, the AES/EBU RAVE must be acting as the network conductor. To guarantee that the RAVE configured for synchronization to the AES “master clock” is always the conductor, it is recommended that the unit’s conductor priority level be elevated via software with the “condPriority” variable (refer to the CobraNet datasheet variable descriptions). Additionally, the AES input stream at channel 1 must be configured for a 48 kHz sample rate.

The advantage to using the AES “master clock” synch method is that all local audio clocks are derived directly from the AES master clock stream. As with all system synch methods, all performers slave to the network conductor. Additionally, since the network clock is distributed throughout the system, all AES receivers and transmitters will be synchronous to the AES master clock sourced by the AES receiver at input 1 of the conduc- tor unit.

The disadvantage to using the AES “master clock” synch method is that the on-board PLL is permanently disabled when the jumper at header J39 is in the “AES clock” position. If the RAVE device loses the conductor role it will no longer have clock pullability and will likely lose synch to the network.