NEXUS Digital Audio Routing and Interconnect System

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XDSP Signal-processor Board

Generic Signal-processor Board for the NEXUS System

40-bit floating-point processing
Full NEXUS integration; operation via the graphical user interface
Various signal-processing modules such as compressors, limiters, noise gates, expanders and delay units available

XDSP Signal Processor Board

The NEXUS is more than just a routing system or audio network: The XDSP board provides digital signal processing for the NEXUS system. A variety of software-based processing modules are available, for example, various equalizer types, dynamics processors, gain and signal delays. Depending on the specific application requirements, multiple XDSP boards can be implemented in NEXUS Base Devices.
The board is also used for specific system options such as mix matrices or the extensive intercom matrix.
Compared with the previous version, the performance of the XDSP04 board has been significantly increased while maintaining the modest current draw: Thanks to its fivefold computing power, a single XDSP board processes 64 faders, 56 dynamics modules, 14 EQ/delay sets, or 16×8 - 1 mixers.

Signal processing inside – NEXUS provides multiple alternatives for that: the XDSP, XFAD, and XJU processor boards. The XDSP and XJU boards are available as versions with no front panels; these boards can be installed behind front panels of other 8-DU boards to save space.

Globally Consistent Operation

The signal-processor functions can be applied anywhere on the routing system and are controlled using the NEXUS software regardless of the board‘s physical location. The parameters are set in the parameter or equalizer windows, specific control windows, or generic module-parameter windows.
The graphical user interface handles DSP resources like external effect units. The modules are displayed as extra I/O resources in the matrix windows and are inserted into the signal path by setting crosspoints.

Economical Solution

The XDSP not only provides the benefits of hardware/software integration (there is no need for external units) but also allows the number of NEXUS I/O boards on the system to be reduced to a minimum. Moreover, no extensive installation of electrical and mechanical devices is necessary either.

Signal-processing Modules

Stage Tec configures the signal-processing functions according to customer requirements. A multitude of processing modules can be implemented in addition to the standard version with equalizers, delay, and gain.

› Gain and Delay Settings The gain can be set using a graphical slider, and the audio signal can be delayed. The maximum delay time (up to several seconds) depends on the number of delay modules configured per board.

XDSP Signal Processor Board - Parametric Equalizer

› Parametric Equalizer The parametric equalizer offers multiple filters that allow for adjusting the frequency, Q, and gain. In addition to the standard peak filters, high/low-shelving, high/low-pass, and notch filters are also implemented. Dedicated buttons allow individual filter bands or the entire EQ to be reset or bypassed.
Graphical views of the filter curve currently being adjusted and the overall frequency-response curve are provided. In addition, the dialog window shows the current output level. A copy function enables the settings to be applied to other equalizers.

› Dynamic Units Various DSP resources such as compressors, limiters, noise gates, or expanders are available for dynamics signal processing. The control windows of the dynamics units have a clear and modular structure. Settings such as threshold, gain, attack, hold, and release allow for extensive creative and technical processing. In addition, the results of the dynamics processing are graphically displayed.

Compressor The compressor is used for reducing dynamic range. The threshold can be set between -40 and 0 dBFS, and the compressed signal gain can be raised by 0 to 63.8 dB. The time-constant parameters can be adjusted to suit the program material; for example, attack times within a 20 µs to 399 ms range can be applied, while the hold and release times can be set anywhere in the range 10 to 10,000 ms. The full range of compression ratios can be set between uncompressed (1:1) and limiting (1:50).
Limiter The limiter allows the output level to be restricted to a specified value. The adjustable parameters are largely the same as the compressor; however, the compression ratio of the limiter is fixed at 1:50.
Expander The expander allows the dynamic range of a signal to be increased below an adjustable threshold. The threshold can be set within a range of -65 to 5 dBFS, the expansion ratio between 1:1 to 15:1. The gain and time parameters are the same as the compressor.
Gate The noise gate dynamically mutes signals with a level below the adjustable threshold. This is useful, for example, when interference occurs. Unlike the expander, the expansion ratio is fixed to 50:1.

› Crossover Crossover modules are available for connecting to active speaker systems. These modules are also controlled in the NEXUS control program parameter window. The universal processing modules enable a crossover frequency in the range of 20 to 20,000 Hz to be set while the Q can be toggled between 6, 12, 18, and 24 dB/oct.

› Sample Delay Delay units providing extremely short delay times (max. 500 samples) with small step widths are available, for example, for compensating latencies between multiple speakers. Unlike standard delay units, these modules feature a step width of one sample. When using a sample rate of 48 kHz, this corresponds to a delay time of 20 µs, equivalent to a distance of 7 mm.

XDSP Signal Processor Board - Summenmatrix

› Mix Matrices Mix matrices allow for »blending« multiple inputs to a single output signal. The input signals are not just routed but internally mixed using an XDSP signal-processor board. The mix-matrices option is fully integrated into the NEXUS system; the matrices are operated using specific mix-matrix windows similar to the usual matrix windows.

› Mono Mixer The mono mixer allows for mixing (summing) any two input signals (for example, a stereo signal) to a mono signal. The mix-signal level is reduced by 3 dB in order to minimise perceived level differences between the mono and stereo signals (other reduction values can be implemented on request).

› Gain/Delay Matrix A gain/delay matrix is available for directional distribution of microphone or other signals to a distributed speaker system. Due to often quite complex acoustic environments, the sound in fixed installations can be reinforced via a multitude of speaker systems. Individual signal feeds to these systems enable local direct-sound control to be more flexible while muting areas where feedback is likely to occur. The implementation of a gain-delay matrix provides for directional sound reinforcement for all listeners — no matter where they are located. In addition, the large number of speaker systems and power amplifiers improves reliability that can be further optimized by using redundant power amplifiers. The gain/delay matrix allows for defined routing of input signals to outputs. Each crosspoint includes independent mix stages, amplifier settings, and delay lines. The individual parameters are configured during the planning and calibration phases and can be loaded in operation using a NEXUS user interface controller.

› N–1-Matrix N-1 matrices are available, where routing can be performed via NEXUS or external controllers. N-1 ma-trices allow for communication between multiple partners where each individual can hear every partner’s (speech) signal except his own.
A full 16 - 16 matrix can be realised on a single XDSP04 board. Multiple N-1 matrices can be cascaded to construct larger matrices.
Additional mixing Output Monitor and Output Mix outputs enable some or all signals to be monitored and / or recorded.

Customer-specific Signal Processing

The XDSP board is designed as a generic signal-processing board. The signal-processing functionality depends on the operating system. The processing modules listed above should be thought of as examples. The range of modules is continuously being extended.

XDSP04 Specifications
Signal-processor modules	The signal-processing functions are configured during the project phase as required by the customer. The number of XDSP boards depends on the number of functions required. The following functions are currently available: level/delay setting, parametric EQ, compressor, limiter, expander, gate, crossover, sample delay, mix matrix, mono mixer, level-delay matrix, N-1 matrix.
Data formats	internal NEXUS audio-signal format (24 bits)
Data formats	synchronised to the system clock
Inputs and outputs	unlimited
Inputs and outputs	64 outputs
Computing power	The following signal-processing modules can be computed on a single XDSP04 board. If multiple processing modules are mixed on a board, the maximum number of modules will decrease accordingly (reference values @ 48 kHz).
	faders	64
	fader-delay combinations	24
	dynamic units	56
	6-band-EQ	48 (w/o delay)
	8-band-EQ	44 (w/o delay)
	12-band-EQ	36 (w/o delay)
	6-band-EQ	24 (with delay)
	8-band-EQ	24 (with delay)
	12-band-EQ	24 (with delay)
	30-band-EQ	14 (with delay)
	mono mixers	64
	4-in-1 mixers	32
	8-in-1 mixers	16
	16-in-1 mixers	8
Computing accuracy	internal	enhanced 40-bit floating-point format (compliant with IEEE 754/854), 32-bit mantissa/8-bit exponent
Computing accuracy	bus	32 bits
Sample rate	up to 96 KHz (NEXUS system clock)
Signal processors	ADSP 21062L

Stage Tec Entwicklungsgesellschaft für professionelle Audiotechnik mbH, D-12459 Berlin, Tabbertstr. 10
Phone: +49 30 639902-0, Fax: +49 30 639902-32, , © 2002-2008 Stage Tec Berlin

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