Sonifex has released the AVN-GMC PTPv2 Grandmaster Clock – the company’s first product for use in Ravenna networks since joining the Ravenna audio-over-IP group.

Sonifex AVN-GMC PTPv2 Grandmaster Clock

IEEE 1588 PTP (precision time protocol) is used to synchronise all the nodes within a network. To achieve this one of the nodes must become the master clock and distribute time packets to the others. The AVN-GMC is designed to perform this role simply and accurately, acting as a GPS receiver and enabling sub microsecond synchronisation between all nodes.

Ravenna (with its AES67 subset) allows distribution of audio across a network. For this to be possible, each of the nodes needs to be time synchronised with one another. Ravenna uses PTP time stamping to achieve this, which distributes the network time but also works out the latency involved in the delivery and adjusts the time at each node accordingly. Unit configuration is achieved easily either with the front panel controls or the webserver, including the setup of the PTP profile.

In normal operation, the unit has PTPv2 time stamping resolution to 8ns. The AVN-GMCS uses a combination of a GPS receiver, a PLL (phase lock loop) and a specialist onboard clock device to create the precise, low jitter clock signals required to drive the physical transceiver’s time stamping circuitry, also providing holdover if the GPS signal is lost. The specialist on board clock is available in three different types: TCXO (Temp controlled), OXCO (Oven controlled) and CSAC (Chip scale caesium atomic clock), which provide between 1 part per million and 0.00050 parts per million accuracy if the GPS signal should be temporarily lost.

A separate clock input can act as an alternative reference source to GPS. Clock outputs, driven from the physical transceiver, can be used to provide media clocks for external equipment local to the AVN-GMC when it is in both ‘master’ and ‘slave’ states. The clock outputs are available as AES-3id and word clock at 32, 44.1, 48, 96, 176.4 and 192kHz. A variable PPS output is also available to provide an external clock accurate to the PTP system timing.

The built-in web server or front panel LCD can be used to configure the unit. Front panel LEDs show the synchronisation status, GPS lock and the status of the AC and DC power supply inputs.

Four general-purpose outputs indicate critical states for the unit using a 9-way D-type connector mounted on the rear panel. Pull down when active pins are supplied for GPS lock status, external sync present, AC power present and DC power present.

The unit has a front panel power button and dual power connectors - an IEC mains input and a 12V DC input, which allows the AVN-GMCS to be used for both studio and mobile installations. Moreover this allows for a secondary power source to reduce the effect of power down events. In any case, the unit monitors the status of both power sources and displays this on the front panel. In power off situations, a super capacitor is used to keep the GPS receiver powered in a low power mode for more than 20 hours, enabling the receiver to regain lock immediately rather than having to ‘cold’ start.


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