Components

NEXUS Base Devices are interconnected using standard duplex fibre-optic cables connected to XFOC boards. These lines transfer all audio and control information required for audio-network operation — there is no need for any additional cabling.
An XFOC board offers two independent duplex ports with 128 audio channels each for connecting separate Base Devices. The extra port can also be used to extend the number of channels or to provide a redundant connection.

The fibre-optic interface board provides two independent ports with 128 inputs and 128 outputs each.

256 Audio Channels on a Single Board

A fibre-optic interface board supports the simultaneous transmission of 2×128 audio channels. Using both ports of a single XFOC board allows for the transmission of all the Base Device time slots. Multiple XFOC boards can be installed into a NEXUS Base Device for connecting further Base Devices or implementing redundant lines.
The audio channels are transferred over the optical lines with their full 30-bit resolution (24-bit audio plus ancillary data) in an uncompressed format. This provides for completely transparent exchange of audio signals between two Base Devices.

Control Information Included

The control data forms a buffered transparent transmission channel asynchronous to audio and sync data. Control data is mainly used for communication between Base Devices (system control) but can also be utilised for routing ancillary data on the NEXUS network.

Sync Information

Sync data transferred on optical lines includes both the internal wordclock and the bus clock of the sending Base Device. Each Base Device can be synchronised to any fibre-optic line. The internal wordclock is also made available at the wordclock output of the XCPU controller board. Therefore one Base Device can act as the master device on the NEXUS network and all other Base Devices will synchronise to it via their fibre-optic lines. There is no need for extra wordclock lines between the Base Devices.

Latency Compensation

A NEXUS network can contain fibre-optic lines of various lengths, from a few metres to many kilometres or miles. Shifted wordclock phases between Base Devices caused by optical latencies are reliably corrected. Acting as master, the XFOC board analyses the phase relation between the received data stream or wordclock and the system clock and adjusts any differences.

Transmission Reliability

There are many factors that ensure extremely resilient, reliable, and trouble-free signal transmission on the audio network:

› Optical Fibres  Due to the use of optical fibres, the Base Devices are entirely electrically isolated from each other. In addition, the cables are highly fire-resistant (material-dependent) and entirely immune to ESD and EMI.

›  Error Recognition  The system automatically detects broken lines, sync loss, input-level, and decoding errors.

›  Redundancy  Increased safety is achieved by setting up redundant fibre-optic lines from the same or another XFOC board. In case of failure, the controller automatically switches from the primary connection to the redundant one.

›  Independent Ports  The largely independent configuration of the two ports on a board provides for high reliability against hardware errors when setting up a redundant line from the same board. Data loss at changeover is prevented as the current audio sample is always memorized.

›  Data-Stream Signatures  A signature is created for the split data stream and is verified by the receiver. This allows for muting the respective board or receiver in the event of an error.

XFOC07 Fibre-optic Interface Board

XFOC A  Fibre-optic Interface Board

The XFOC A is a passive adapter board that converts fragile LC optical ports to robust Neutrik optical ports in a 1:1 relationship. Each XFOC A can convert two duplex lines. The board can be installed anywhere on the mainframe; however, the length of the LC fibre optic pigtails is limited to approx. 35 cm/13.8".
Each pigtail is simply plugged into a NEXUS LC optical port which requires adaptation. The adapted signal is then available on the Neutrik socket on the XFOC A board.