Q-Sys system leads the development of centralized audio signal processing

Today, there is still debate about decentralized and centralized audio processing. Is it better to use centralized digital signal processing in large audio systems, or to use decentralized multiple signal processors over the network? The discussion seems to have stopped some audio experts a few years ago.
Many audio vendors still support decentralized signal processing, but the founders of the two peak audio companies, Rich Zwiebel and John Britton, think this is an outdated way. The two philosophers first proposed configurability in 1992. The concept of an audio processor.

The biggest argument is whether decentralization is more stable than centralized. In a decentralized process, if one component fails, the rest of the system will continue to work.

Mr. Zwiebel doesn't think so. He said, "Our team of engineers has used both methods. Because there are a lot of devices in the decentralized way , we know that there will be problems. In other words, it is a problem from one point to a lot. Point to possible problems, and any one of them can cause system failure." Today's technology has allowed us to trust one processor, use another backup DSP, and back up the DSP when there is a problem with the primary device. Can automatically take over the system.

The story behind the decentralized DSP

The team of engineers at Britton and Zwiebel began designing DSPs more than 20 years ago, designing hardware and software for the Budweiser media matrix product line. In 1992, the media matrix product was released. It is a centralized processing platform that flexibly inserts DSP cards into the multi-card slot chassis.

Mr. Britton said: "We originally wanted to design for a small fixed installation, but later, we increased the processing card and increased the processing capacity to meet large systems." Multi-card design proved to be very popular.

After the development of CobraNet by the Britton and Zwiebel teams in the mid-1990s, they began to consider placing DSP chips in separate devices and connecting them through the network. Peak Audio finally designed a new product in 1999: Budweiser Media Matrix Nion, which is more flexible and scalable than before.

The Nion processor can be placed close to the input and output devices throughout the campus, as well as for functions that call the entire region. The system design team initially thought that such a decentralized design could also improve the reliability of the entire system, because if any processor is broken, the rest of the audio system can continue to work.

In 2001, Zwiebel and Britton sold the Peak Audio Company to Cirrus Logic. In 2006, they joined QSC Audio. Leading his team to develop a new platform: Q-Sys modernizes the DSP concept and centralizes all audio processing on a single host. The host is based on Intel processing chips that connect inputs and outputs via off-the-shelf Gigabit networks.
Q-Sys centralized processing

　　 Q-Sys was developed by John Britton, Mr. Rich Zwiebel and QSC engineers. Although it is not the only centralized audio processing platform, it is one of the most interesting ones.

The host Core is the brain of the system and is responsible for all audio processing, signal routing and control functions. The host has five models that handle 8 to 1024 channels of audio signals, and multiple hosts can form subsystems in the system to serve larger systems. The Q-Sys host uses a standard Intel multi-core processor to run a Linux-based operating system in real time, using floating point arithmetic to guarantee dynamic range. Q-Sys uses a standard network interface.

Interface machine Q-Sys I/O Frame completes the input and output of audio signals, with GPIO interface and serial port. Each interface machine can insert up to 4 I/O cards, each of which can process up to 4 channels of analog audio input or output, or process more channels of digital audio signals. The interface machine is usually located near the audio source, mixer, amplifier, and speaker, and is connected to the host through Gigabit Ethernet. After plugging in the I/O card, Q-Sys can be connected to any analog audio device. Digital audio input and output cards have become a bridge to other systems.

Users have a variety of ways to control Q-Sys systems, PC or Mac, Apple iPad, iPhone, QSC touch screen, or network-based Crestron, AMX and other central control products.

The host, interface and control devices are connected via a standard three-layer Gigabit Ethernet network, which can simultaneously transmit data, video streams and telephone signals. This is an integrated network.

Sometimes, there is a reason to use decentralized processing in a system. For example, a theme park, each network has its own maintenance staff. However, background music or emergency call sources are centralized and need to be sent to the entire campus. In this case, Q-sys supports "subsystems in the system". In this way, multiple hosts can be dispersed throughout the network. This hybrid approach maintains the advantages of centralized processing, but at the same time maintains a decentralized approach within the campus.

The latency of the Q-Sys network is very low. The end-to-end delay is only 2.5 milliseconds, including analog to digital conversion, network transmission to the host, signal processing within the host, second pass through the network signal to the destination, and finally digital to analog conversion. This amount of delay is about the delay of a person speaking 0.75 meters to us - this amount of delay is hard to feel. Mr. Zwiebel added, "In addition to low latency, all outputs of the system are synchronized for any input."

The mainstream trend of network standardization is accepted by the majority of IT. Because Q-LAN's IP compatibility is excellent, IT departments can manage and monitor Q-Sys networks and system devices just as they do with IP networks. “Design consultants and contractors also like Q-Sys,” Mr. Zwiebel said. “Now they can finally design and edit systems of almost any size, without the limitations of the processor, without having to split the system. Designers can Free to play and achieve their vision. All routing is done in one device, making it easy to switch between any input and output."

Discussion on Q-Sys centralized processing

　　 Mr. Zwiebel said that when he demonstrated Q-Sys to potential users, customers often questioned the system design of centralized processing. “The most common negative argument is that customers feel they need to put the processor in a lot of locations,” Mr. Zwiebel continued. For this, I always ask, “Do you need to disperse the processor or the interface machine?” In most cases, it is the interface machine that needs to be placed in a distributed manner.

“Once the customer is aware of the problem, they usually admit that they don’t really care where the processor is, but I will actually say that you have to consider this. Imagine: the customer is willing to put all the processors in a safe place. Is there an air-conditioned place that can be accessed at any time, or is it possible to disperse the processors in many places, such as a horse-drawn amp or a courtroom that cannot be entered during a meeting?" Customers usually choose the former. More willing to put the processor in their own equipment room.

“Another negative statement I have heard is that decentralized systems are more stable and reliable, because even if one device has a problem, it is only a part of the loss of the system. But in fact, when there is a problem with a device, it is often a big problem. If the bad equipment is responsible for the audio input of the stadium announcer, what will happen? The whole game will stop."

Mr. Zwiebel cited an example of the audio system design that the Peak Audio Company designed for the US Senate in 1999. There are 5 processors in the system. If one device is broken, as happened at the committee hearing, only 20% of the system's functionality is lost. "But the hearing is still unable to continue. It cannot be said: because the equipment is broken, the Democratic Party can't speak, but the Republican Party can continue." Later the hearing had to be cancelled.

Mr. Zwiebel explained that cables and plugs are the most problematic for an audio system. Using 5 independent processors instead of one means adding at least 5 network cables and 10 network cable plugs to important systems. For centralized systems, putting all the processing functions on one chip reduces these cables.

“Another benefit of centralized processing is that it simplifies system design and simplifies the management of design files,” adds Zwiebel. When an engineer uses multiple DSP processors, each processor has its own design file, and the system designer records the specific functions of each device. "This increases the complexity of the system, resulting in system implementation, upgrade, and slow compilation. When the system has problems, it is difficult to troubleshoot the problem. Q-Sys uses centralized processing, and the entire system uses only one main design file, which simplifies the system. Design, implementation, management and system upgrades."

Backup

　　 Any sound system has the potential to fail, and many system designers try to create backups for important distributed systems, but this is difficult and costly. Mr. Britton said that centralized systems are simpler, have lower backup costs, and are more reliable backup devices.

For example, the Q-Sys processing host appears in pairs in the network. When the system detects a failure of the core host, the backup host automatically takes over the system within a few seconds. When the engineer adjusts the settings, any settings are recorded in both hosts at the same time, so the backup host can always take over in real time. Each Q-Sys device has one master and one backup network port. Two completely independent networks can be used, so if there is a problem with any of the networks, whether it is a switch problem or a cable problem, the other network can take over the system automatically and simultaneously.

In addition, the centralized system allows designers to back up the I/O interface and even back up the amplifier in high-importance situations.
IT compatibility and AVB

　　 Mr. Zwiebel said that there has been a lot of discussion about AVB recently, that is, audio video bridge, which some people in the industry think is the standard of the network. One advantage of AVB is that it transfers data fast. The AVB standard requires an overall network delay of less than 1.024 milliseconds.

"But standard Gigabit Ethernet, using existing components, has a network latency of less than 1 millisecond, which is small enough," explains Mr. Zwiebel. "From an IT perspective, AVB is non-standard and requires a 2-layer network instead of a Layer 3 Internet protocol." This has led to AVB's requirement to use AVB private switches, limiting the advantages of leveraging existing IT architectures. Data is transmitted over the AVB network through CISCO or HP routers, and the two brands are installed in at least 80% of the world's networks.

Zwiebel and Britton believe that today's audio networks should be fully compatible with popular network devices, just like Q-Sys. In addition to distributing low-latency audio signals over a local area network, it should also support long-distance transmission of audio streams over a wide area network or the Internet.

A centralized processing platform running on an IP network should follow the mature practices of the computer industry. "Audio signal transmission should not require a separate network architecture," Britton said. "IT departments can use the same quality of service as voice IP transmission or IPTV to set up an audio transmission system to ensure that audio signals have a reasonable transmission priority. It is well known today."

Is centralized processing a future trend? Mr. Britton said: "We will continue to go." “The centralized processing we have adopted has provided a very powerful processing platform, reducing development effort and reducing system complexity, while at the same time, like the powerful processors and network interfaces in the mainstream market of the computer industry, centralized The system's software has also been given a long life."

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