The Cost-Effective AES/EBU Output Board for NEXUS Base Devices

The XET card connects a NEXUS network to any AES3-enabled audio device. It transfers up to 8 audio channels in 4 AES3 data streams with transparent user bits.

The NEXUS XET output board provides four dual-channel outputs according to AES/EBU or S/PDIF specifications. For individual requirements, the board is available with a variety of connector types: XLR, BNC, Cinch and optical TOSLINK; versions with RJ45 and D-Sub connectors allow all signal lines to be routed together via the respective connector in an installation-friendly manner. The XET-OR module variant offers additional parallel outputs as standard - optical TOSLINK and electrical RJ45. The XET-S front panel expansion module, which provides an additional output, is also available for the standard versions. An XLR version can be expanded by XET-S to include parallel optical connections, for example. The four stereo channels can be routed independently of each other - even as mono channels - in the NEXUS system. The board also supports legacy mode, in which a single-channel audio signal is transmitted at twice the sampling frequency via a standard AES/EBU port.
In the XLR version, the front panels can be detached from the card and connected via a ribbon cable to be installed elsewhere in the Base Device, for example in a plane without a bus circuit board. The space requirement of the XET-X board is then reduced to 4 TE.

DSP for Noiseshaping and Dithering

The 24-bit NEXUS audio signal can also be output in 16-bit or 20-bit resolution for external devices. In order to achieve the highest possible audio quality, the word width is converted by the internal signal processor using a dithering algorithm. This audibly minimizes inevitable signal errors that worsen noise and distortion ratios.
In addition, the noise energy can be transformed into frequency ranges to which the human auditory system reacts less sensitively with the optional "Noiseshaping" function. The noise reduction achieved in the range below 1 kHz is about 15 dB; in the critical range around 3 kHz it is still about 10 dB. The "Noiseshaping" function is calculated using a 5th-order algorithm.
In addition, the signal processor integrated on the module enables phase rotation, level adjustment and dynamic limitation of the output signals. These parameters can be set via service software.

Also Free Sampling Rates

The XET board is equipped with sampling rate converters for the connection of external devices that are operated independently of the system clock or with other sampling frequencies. A precise clock generator with the standard frequencies 32 kHz, 44.1 kHz and 48 kHz is provided on the board for this purpose. The output frequency can be selected to be two or four times this frequency - also separately for the respective outputs. A free, system-independent sampling rate permits the use of the optional XOSC generator module, which is available for a wide range of clock frequencies depending on requirements.
In addition, the circuit board offers an input for external word clock signals to which the sampling rate converters can be synchronized.
This input can also be used for self-sufficient synchronization to a neighboring AES/EBU XER input card, independent of the system clock. Several cards, connected via additional flexible circuit boards, can even be cascaded in this way.
In order to ensure identical runtimes and phase positions at the different outputs, the sampling rate converters of the card can be synchronized with each other. This is useful, for example, for multi-track machines whose inputs are fed via AES/EBU. The sampling rate converters are synchronized automatically at identical frequencies.
The sampling rate converters can be activated separately for each stereo pair using the operating software.

Additional Information in the Data Stream

Additional information from AES/EBU data can be transparently transferred in the NEXUS system or completely regenerated: The channel status can be set to "Professional" or "Consumer" mode independently of the input signal.

Test Generator

For test purposes the board is equipped with a signal generator which can generate a sinusoidal signal as well as a low amplitude noise signal.
Downloads :

NEXUS / NEXUS Star Data Sheet