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DACS: System Description
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System Description

In stock configuration, the unit shall provide thirty-two line-level audio inputs capable of receiving balanced or unbalanced audio signals. Eight balanced and eight unbalanced line-level audio outputs shall also be present on the rear panel of the unit. These outputs may be converted to all balanced or all unbalanced merely by changing modules. Depending on the mode and hardware configuration of the mixer, all inputs and outputs may not be available at a given time. The digitally-controlled mixer circuitry shall behave in a logarithmic fashion, to match the response of the human ear. The mixer shall provide from 0dB to 63dB of attenuation capability, in 1dB steps. Additionally, near-infinite attenuation ("mute") shall be provided for each input channel. This dictates that the digital controller for the audio mixer shall have at least 6 bits of resolution. Digitally controlled switches shall be used to reconfigure the audio paths of the mixer. These switches shall be of the ``clickless'' type, such that signals may be re-routed without any undesirable noise entering the system. The unit shall incorperate an 8-bit A/D converter and appropriate analog multiplexer and driver circuitry to allow monitoring of all input and output signals, after the input buffers and before output drivers. This setup shall form the basis for a digital VU meter. The VU meter shall be capable of reporting signals from -10dBu to +18dBu. The converter shall function linearly, with any necessary logarithmic conversion taking place in software. This VU data can be displayed on the mixer unit itself via its LCD and/or transmitted over the microprocessor's serial uplink, to be displayed on a host PC or the DACS control board. Mixer modes and other relevant information shall be displayed to the user via an LCD panel on the front of the unit. A single LED shall indicate serial link activity. Another LED shall indicate that the unit is powered. The unit shall be constructed in a modular fashion, such that future upgrades are possible by simply adding or changing cards. The choice of output channel boards shall be left to the user, allowing a mixer with all balanced, all unbalanced, or half balanced and half unbalanced outputs to be constructed. In addition to the upgrade capability, the PC boards shall be designed such that a larger model mixer unit can be built without re-engineering the electronics. Future upgrade options may include, but are not limited to: equalization modules, microphone preamplifier modules, DSP effects engines, and digital audio interfaces (for AES/EBU and S/PDIF-compliant digital audio devices). The unit shall incorperate linear internal power supplies. Switching power supplies are unacceptable in this unit due to the large quantity of electrical noise they create. Separate power buses for digital and analog circuitry shall be provided, to reduce digital noise in the analog portions of the mixer. These supplies shall be sufficiently capable of powering add-on modules. External connection to these supplies shall be made via a standard IEC power connector at the rear of the unit. This power entry unit shall be of the type that filters EMI and RFI interference. It shall be appropriately fused and switchable via a front-panel rocker switch. The mixer unit's microcontroller shall communicate with the rest of the DACS via an RS232 3-wire serial interface. This interface shall be presented as a 9-pin female D-subminiature connector, and shall be wired per the RS232 9-pin Data Communications Equipment (DCE) spec. This allows direct connection to a host PC with a straight-through cable. The serial communication shall take place at 19200 baud. The unit shall be referred to as DACS Model 411 - Modular Automated Audio Mixer.
next up previous contents
Next: Specification Sheet Up: Mixer Unit Previous: Mixer Unit   Contents
Steve Richardson 2000-07-06
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