28 l December 2012
www.psneurope.com
broadcastfeature Hello, Mr Chips!
While the adoption of FPGA ICs continues to increase, it may not necessarily be at the expense of traditional DSPs, whose usage remains widespread. David Davies takes a peek at the present – and possible future – of audio processing
DiGiCo FPGA-incorporating processing engine
REFLECT ON the past 10 years of audio processing development and it won’t be long before your attention alights on four letters: FPGA. Implemented most extensively in large-format mixing consoles, FPGAs (field programmable gate arrays) have heralded a new era of processing in which flexibility of purpose and extensive I/O management are powerfully combined. Tino Fibaek, general manager
of rejuvenated Australian digital audio equipment manufacturer Fairlight, encapsulates some of the primary benefits: “Besides simplifying manufacturing and improving reliability, the transition to FPGAs have another key benefit: flexibility. FPGAs have enabled us to create a new paradigm of ‘Virtual Hardware’. It is dedicated, optimised, real hardware logic cells, electrically interconnected to efficiently do a specific task. But unlike traditional circuit boards, FPGAs can be completely re-routed and re-tasked by simply issuing a new software release. It’s the best of both worlds.” Fairlight with Crystal Core;
Calrec with Bluefin; DiGiCo with Stealth Digital Processing...
“FPGAs are good for a huge number of repetitive tasks, but they are not very intelligent” John Stadius, DiGiCo
all these and many others have nailed their colours to the FPGA mast. But while costs have fallen, it’s a technology that can be expensive to introduce, and for some observers, is still not as fertile in coding development libraries and programming expertise as traditional DSP. The overall impression from a
week of speaking to processing specialists and customers is neatly encapsulated by Denis Labrecque, who handles pro-audio business development, embedded systems products and technology for Analog Devices. “What I have seen for many years now is that standalone DSPs coexist quite nicely alongside FPGA systems and I believe will continue to do so for the foreseeable future,” he remarks.
THE SCIENCE OF FPGAS Just like MADI – currently in the midst of what is arguably its greatest period of popularity, a mere two decades after it was first unleashed on the world – FPGA is really nothing new. The concept had been gaining currency for several years before Ross Freeman and Bernard Vonderschmitt – co-founders of programmable technology specialist (and latterday AVnu Alliance co-pioneer) Xilinx – devised the first commercially-oriented FPGA, the XC2064, in 1985. It wasn’t until the 1990s, however, that the
pace of rollout truly picked up, with telecoms, automotive and industrial applications beginning to make widespread use of FPGA. The core premise behind FPGAs is relatively concise. They take the form of an array of programmable logic cells, each of which executes a simple logic function defined by a user’s programme. An FPGA can possess anywhere from 64 to more than 20,000 of these cells. Easily and infinitely reprogrammable, FPGAs can deliver significant performance gains and, despite being customised at the point of use, may be produced in high volumes.
Tino Fibaek highlights FPGAs’ “one obvious advantage over DSPs: their efficiency in concurrent applications, achieved by using multiple parallel processing blocks. Coupled with their flexibility to allow the embedded systems designer to tailor the device to match their application’s demands as closely as possible, FPGAs can achieve the highest possible throughout with low cost-per-channel.” John Stadius, technical
director of DiGiCo, picks up the theme, noting that the FPGA approach to audio engine design “turns everything on its head because we can get heavily into the realms of parallel processing. A small block of logic, multipliers, etc, in an FPGA can be allocated for, say, filters. A single filter block can provide us with 1,500 bands of EQ at 96kHz. Typically, a channel strip would require eight bands of EQ: two for the input hi-lo filters, four for the four-band EQ, and two bands for a gate key filter. This adds up
to 1,024 bands for 128 channel strips, so we could use the remaining bands to implement, for example, 12 32-band graphic equalisers.” The capabilities of larger FPGAs are considerable, continues Stadius: “The logic resources used by this filter block represent just a small proportion of the available logic in a larger FPGA, so as well as the filter logic we can have other processing modules to implement features such as dynamics processing, bussing, dynamic routing matrices, matrix delays, meters, etc. “Because each module is self- contained, we don’t suffer the bandwidth issues that one would otherwise have with a single shared DSP bus, although there is one area that places huge bandwidth demands with large-scale engines. This is the main routing matrix but as ever, this can be solved in FPGA by clever ways I’m not going to reveal.” Driving the point home, he remarks that for DiGiCo the use of FPGAs to process audio is “a no-brainer”. Soundcraft’s R&D manager, Chris Gomm, is similarly FPGA-evangelical. He highlights Soundcraft’s use of FPGAs in multiple areas of product design – precision audio summing, low latency digital audio format conversion and user interface control. “FPGAs are a fundamental part of sophisticated digital systems and are found wherever high levels of application- specific customisation are required within a digital system,” remarks Gomm. Their ability to help maintain
low latency is especially beneficial, he notes: “One of the great strengths of FPGA technology is that it is possible to create very fast, very closely coupled systems within the device that enable us to move audio between
Soundcraft’s Si Compact processing engine
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