White Paper Infinity Processin P ng
Generallyy speaking ma ajor steps in audio design only happen everry decade orr so. The firsst realistic larrge scale digital mixer was de eveloped in the mid 80’s. This me 25,000 ICss, 80 units of rack space and a required som 6kW of powe er just to make e a 48 channe el mixer! In ord der to reduce this to a slightlyy more practiical size custo om silicon was designed d for th he next generration of mixe ers. This doubled d the channe el count in one o third of the t space and a quarter of o the powerr. This proce ess ut each develo opment was slo ow and costly. continued bu me of age wh hen the SHAR RC Digital mixers truly cam chip became e available aro ound 1994, th his offered mixxer designers off the shelf silicon which runs well in clusters, (aud dio processing g is a highly parallel p task; you y have to proccess many cha annels at the same time) has h long word le engths and su uitable softwa are developme ent tools are ava ailable to creatte audio proce essing function ns. In the mid ‘90 0s up to 100 or o more of the e first generatiion SHARC chips were used to t create a larrge scale mixiing desk, the DSP D took nin ne units of rack space and a consumed some 500 wattts. Over the next 15 yea ars, successive versions of these chips became mo ore powerful, goiing from some e 120 Mflops to 2700 Mflop ps. (Mflops = Million Floating Point operations per Seco ond ommon way of o defining pro ocessing powe er). which is a co The latest Studer use of SHARC chipss in the Vista a 1 o SHARC chips uses only 8 of the currentt generation of to mix nearrly the same e number off channels and a consume only 25 watts. Th here has been n about a 22 fo old increase in the processing power off these SHAR RC chips over the last 15 yearrs or so. Field Pro ogrammable Gate Arrays (FPGAs) ha ave become quitte widely use ed in the pro ofessional aud dio industry and they have also a become larger over the t ommitted “sea of years. They are basically a huge unco gates” that may m be linked d together to form multiplie ers, registers, adders and so forth. f Howeve er, programmiing them to proccess audio is more comple ex. For examp ple, changing a multiplier m used d to calculate e an FIR filter (a common tassk in audio processing) p in nto a routine to calculate FFT Ts (such as metering m displa ay) is hard to do and prone to o errors. The lack of suitab ble developme ent tools to build d the FPGA co ode in the field also makess it impossible fo or customers to construct their own DS SP configuration ns. Flexibility of configuration is a hu uge benefit to cusstomers as it allows them not n only to ada apt their mixer DSP D to meet th heir needs when they install it. It also allows changes to the con nfiguration affter
STUDER - Infinity Core C - White Paper
pu urchase, for example th he provision of surround d ch hannels with the advent of high definition n TV and new w prrocessing algo orithms such as automatic c mixing. Forr this reason FPG GAs are not sseen by Stude er as suitable e for large scale audio a signal processing for the future. The use off both SHAR RC and FPGA A devices forr au udio processin ng always requires significa ant R&D; each h tim me a new gen neration of chips become av vailable much h R& &D effort musst be invested into new board design and d maybe new pro ogramming. F For this reason n, most audio o SP engines are replaced only every 5-7 years, in n DS orrder to maximiise the return on R&D inves stment. Standard CP PU chips, the x86 types as used in huge e nu umbers for ge eneral compu uting, are very y suitable forr no on-real time signal processing. They are easy to o prrogramme, ma any developm ment tools are available, the e sh hipping volum mes are huge,, so much efffort goes into o de esigning the chips and th he PCBs use ed to supportt them. Of vital sign nificance is the processing power of x86 6 ch hips has incre eased some 5 5,000 fold in the same 15 5 ye ears that SHARC chips havve increased in n power some e 16 6 fold. This doubling d of p power every 24 2 months iss kn nown as “Mo oore’s Law”. The dream m is to take e ad dvantage of th his effect in Stu uder’s new ge eneration DSP P en ngine. Modern n CPUs use m multiple hardw ware “cores” to o ob btain the huge e processing power offered d today (clockk sp peeds have reached a plateau due to physicall co onstraints). Currently high--end CPUs have h 8 to 10 0 co ores, each of which may be e set to run 2 threads thuss do oubling the processing power. This s “multi-core”” technology is very suitable for large scale audio o prrocessing due e to the para allel requireme ents of audio o mixing engines.. However, th here is a kille er problem; x86 CPUs are e esigned as general g purpo ose processorrs and everyy de no ow and then, they t stop to do o some house ekeeping such h as s RAM refresh hing or temperrature sensing g. This is not a prroblem for most m computin ng, a momen ntary “pause”” wh hilst saving a file is of no consequence e but a single e missed audio sa ample results in an unaccep ptable click. In order to avoid this prroblem, normal x86 based d au udio signal prrocessing add ds audio buffe ering or delayy so o that CPU in nterrupts do not affect the flow f of audio.. Fo or real time “live” audio, th his delay or latency l is nott ac cceptable. The buffering a also reduces the efficiencyy an nd thus reducces the channel count. Stud der has found d
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a clever way of isolating several of the CPU cores using a special version of Linux and stopping these cores from being interrupted. One core is left to run the desk communications and housekeeping whilst the rest of the cores concentrate on audio DSP for the highest channel count, without the need for buffering and the consequential audio latency.
Credits: Written by Andrew Hills, Product Director STUDER Professional Audio GmbH. Regensdorf, January.2014
High end “Commercial off-the-shelf” (COTS) server boards are now available for the Intel E5 series processors. Two E5 processors may be fitted; each processor has 10 physical cores. Each physical core can run two threads or virtual cores thus doubling the processing capacity. Studer has achieved some 25 fully equipped (high quality EQ, Dynamics, Insert, Pan and fader) audio channels of processing on each virtual core, thus offering some 50 channels (mono equivalent) per hardware core; a dual processor board can thus process well over 800 channels even allowing one core for control and housekeeping. Clearly having developed this technology, the scalability offers both expansion of channel counts as processors with more cores become available (72 core processor chips are on the horizon) and the possibility of modest channel counts on basic COTS hardware for smaller mixers. More channels for the same money or enough channels for less money. The final part of this new concept is the need to provide a suitable audio interface system to connect the huge number of audio channels into and out of this new core. Studer has designed a new high capacity digital audio interface called A-Link. This fibre based audio interface uses a 3Gb data rate to offer 1536 audio channels per connection. A new PCI express card has been designed to fit into the COTS server board discussed above. This card is fitted with 12 A-Link interfaces capable of over 10,000 inputs and 10,000 outputs offering the huge I/O interface counts required of this new processing engine. We believe this new Infinity DSP engine will prove to be a significant milestone in the development of digital audio consoles and become a standard in the years ahead. We now have 800+ channels in 5ru consuming 600w in this DSP engine. In comparison with the DSP of the mid 80’s, as discussed at the start of this article, we now process twenty times the number of channels in a sixteenth of the space using one tenth of the power. That’s progress!
STUDER - Infinity Core - White Paper