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Distributed Vs. Centralized Audio Processing

May 13, 2013 3:40 PM, By Don Kreski

Peak Audio founders say the distributed DSP model is obsolete.

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Q-Sys Centralized Processing Explained

Q-Sys, developed by John Britton, Rich Zwiebel, and other engineers at QSC Audio, is not the only centralized audio processing platform, but it is one of the most interesting.

The Core is the brain of the system, handling all audio processing, signal routing, and control functions. Cores come in five sizes, handling from eight to 1024 channels of audio, and Cores can be combined to create a larger system of systems. Q-Sys Cores use standard Intel multi-core processors running a hard realtime Linux-based operating system, while the signal path employs a floating-point format to preserve dynamic range. Q-Sys employs standard off-the-shelf network interfaces as well.

Q-Sys I/O frames handle audio inputs and outputs, as well as GPIO and serial control. Each frame can house up to four I/O cards, and each card can handle up to four channels of analog input or output, with higher channel counts for the digital audio cards. I/O frames are normally located near the audio sources, mixing desks, amplifiers and loudspeakers, and connected back to the Cores via a Gigabit Ethernet. With the appropriate I/O cards, Q-Sys is compatible with any analog audio device. Digital audio I/O cards provide a bridge to other systems.

Users can control a Q-Sys audio system from a PC or Mac, an Apple iPad or iPhone, from QSC touchscreens, or from Ethernet-based control systems by Crestron and AMX.

Cores, I/O frames, and control devices are linked via a standard, Layer 3, Gigabit IP network which can be configured to simultaneously carry data, streaming video, and telephony traffic—a converged network.

There are times where distributing processing within a facility makes sense. An example might be a theme park, where each LAN is maintained by its own staff. Yet centralized sources, such as background music or emergency pages may need to be fed to the entire park. In this case, Q-sys supports a "system of systems" approach, with multiple Cores distributed on an enterprise network. This hybrid approach keeps all the benefits of centralized processing while distributing specific processing systems throughout the facility. Latency in a Q-Sys network is very low. The total end-to-end latency, including analog-to-digital conversion, transmission across the network to a Core, processing in the Core, a second pass across the network to the destination, and the final digital-to-analog conversion, is just 2.5 milliseconds. That’s roughly equivalent to the time it takes for sound to travel to your ear from a person talking 2.5ft. away—an imperceptible delay. "In addition to this very low latency, all outputs are exactly in sync from any input," Zwiebel explains.

This mainstream, standardized approach to networking has been very well received by IT managers. Since Q-LAN is IP-compatible, IT departments can manage and monitor the Q-Sys network and system components using the same best practices as they would converged IP networks. "Design consultants and sound contractors love Q-sys as well," Zwiebel says. "For the first time, they can design and program a system of almost any size without any sub-segmentation due to processor constraints. This ability to freely design a system can be a big benefit in getting exactly what they envision. And with all the routing in one box, it’s easy to switch any input to any output in the facility."

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