SR/Live Thu, August 28, 2008

ENTERING THE LIVE SOUND ARENA
With proven capabilities in producing DSP systems for multi-channel audio management, Allen & Heath felt it was time to expand the systems and move from install products into mainstream live-sound mixers.

The finalization of the spec for the mixer took a number of years, with the product changing numerous times
as various key influencers and engineers were consulted. The specification for the signal processing and the system architecture took shape quite quickly but the control surface was a completely different matter. Over the course of three years during which Carey Davies and the author evaluated a lot of proposals and several prototypes, the final design for the iLive evolved. To turn the product ideas into reality, Rob Clark and Antony Jackson would lead the development team.

The iLive system as it is now was first shown to Allen & Heath’s distributors as a working prototype in 2004. However the company was not prepared to release the product until it was sure that it was reliable, great sounding, and easy to use. The hardware and software went through many changes and developments to
enable the console to meet it’s goals, and even now, the development of the software is ongoing, as new features and customer requests are added to the product. The benefits of a well specified and designed digital system is that upgrades to software and hardware are possible so that the value of the investment in an iLive system is retained and the system can grow and be adapted to meet the users’ growing demands.

THE MIX ENGINE
The fundamental design principles for iLive were that the processing should be readily available on all of the inputs and outputs, the latency of the system should be as low as possible, the audio quality should be equivalent to an analog console, and the system should be flexible in how it can be set up and controlled. The main mix-rack, the iDR10, is effectively a “supersized” iDR-8, comprising 64 input channels each with filter, gate, delay, EQ, compressor, limiter/de-esser, and 32 mix outputs each with delay, EQ, compressor, limiter and graphic EQ, together with FX processing. The iDR10 is modular with 10 slots for I/O cards; each card handles eight channels along with the DSP card, the CPU, and a module for clock generation and the distribution of digital audio over networks, initially by EtherSound. A full range of I/O modules are available including 8-channel microphone/line inputs; eight analog outputs; the dual microphone module, which allows a choice of A or B connections to the eight preamp and ADC’s; a digital input module with AES, SPDIF and optical interfaces for eight channels; a digital output module with eight channels of AES, SPDIF and optical interfaces; and a multi-output module that provides 16 outputs to ADAT optical, Aviom, HearBus and iDR-8 units. Further modules will be added to the range as required.

The Texas Instruments PGA2500 programmable preamp was chosen as the best sounding microphone preamp solution for the analog input cards, after exhaustive testing of various systems for low noise 1 dB gainstepped performance.

The low latency of the system is achieved by careful choice of the A-D and D-A converters and the design of the DSP array and interconnects. The DSP is carried out in the iDR10, which is generally positioned on stage near the sources, which means there is no additional latency introduced by having to move mass digital audio signals from the stage to a remote processing unit. The signals are converted, processed, and then re-converted on stage, and the control of the processing is via Ethernet from a control surface. If the connections to the control surface are removed, the audio processing in the iDR10 carries on, set to the last received control data. Ethernet is a true network, so a duplicate control system can be implemented, such as a Wi-Fi linked laptop PC, which can control the iDR10 if the cable link to the control surface gets damaged.

Where the distribution of audio signals is required, the EtherSound ports on the iDR10 can be used, and there are two ports available, each with a specific role. Port A is primarily to provide a link to the surface to enable local I/O at the mix position, as well as carrying the PAFL and Talkback signals but can also serve as a local distribution system, connecting to devices such as speaker systems or other I/O interfaces. Port B is primarily for system expansion to allow signals to be sent to other systems such as an OB truck for recording, another iLive for monitor mixing, or to connect a second iDR10 as an input expander but can also be used as a general distribution audio network.

The core of the audio system is the DSP card in the iDR10 Mix-rack, which has 22 Motorola, fixed-point 56bit DSPs. Although the conversion and transport of digital signals generally uses 24-bit, higher resolution is used where a true benefit is available. The system uses 48-bit precision at key processing points such as in the EQ and 56-bit resolution on elements of the mix buses.

A lot of time was spent in developing a high quality effects engine for live sound. Two of these engines are included as standard and an enhanced DSP card is available for eight effects engines. The presets for the FX are programmed in house and, due to the high quality of the effects engine, it is possible to produce good simulations of industry standard effects and the 24 adjustable parameters in expert mode allow users to tweak any reverb preset to their particular liking.

The primary goal with the DSP processing was to provide all the required processing for dynamics etc on-board so that the FOH rack could be eliminated. This required a lengthy period of algorithm development to ensure the internal processing emulated the performance of the best “industry standard” external devices. This alleviates the need for the engineer to resort to inserted outboard processing.

As well as the DSP software, the operating system for a digital console is a critical area, as an unreliable operating system will kill even the best digital console. With this in mind, it was decided that the basis of the system software should be a specialized and proven real-time operating system with Linux for the graphics environment.

The choice of 48 kHz as the system sample rate was driven by the performance / cost analysis, where the small potential increase in performance at, say, 96 kHz requires the doubling of DSP costs, which is not really justifiable. The fixed processing architecture of the audio system that provides all processing elements on all channels and mixes alike allows management of sample coherency while retaining mix architecture flexibility. The iLive system can also be clocked from a “house” sync on DARS, or synched to the EtherSound network, so that interconnection in digital format can be established without sample rate conversion to maintain best performance.

The iDR10 is a flexible multichannel digital signal processor with AHNet control over Ethernet. Low latency local audio processing is achieved with the parameters controllable from a number of devices which can be connected using standard TCP/IP protocol. Hypothetically, this means you could mix a show with the control surface at home connected over the Internet to an iDR10 Mix-rack on stage while watching on TV (as long as you can put up with the broadcast delays!).

THE CONTROL SURFACE
To control the system, a dedicated live sound control surface was designed from scratch. The development of the surface involved many people who all had a passionate view as to the way they wanted it to work and what they wanted to be able to control. Many different versions of control surface were drawn up before the version that has become iLive was established. The key drivers for the design were ease of use, with no complicated screen menus, compact size, and clear indication of status.

The first key development was the analog-styled channel processing strip. The idea was to have a single control per function, just like on an analog console, and this was extended to include the dynamics processors, which were styled to look and feel like a typical rackmount unit complete with threshold and gain reduction meters.

The second key development was the virtual write on strip, which is essential for banked faders to be implemented. A custom LCD display was designed, and to give further clarity, a multi-colored backlight was included. The backlight allows channels to be color-coded just like using different color fader knobs on an analog console. As motorized fader banks are changed, the write on strip and color change to show the new fader information. As well as showing the channel name, the display gives information on the channel type, pan position and assignment information for the various mixes. A touch control TFT screen was included to provide an interface to set up the system configuration, manage the preset recall system and control the FX units, and it is also used to provide additional information to support the surface controls. The menu structure on the screen is kept as simple as possible, while dedicated menu keys and a data encoder support the touch screen.

To complete the control surface, a local modular I/O rack is provided at the rear of the surface for easy connection of equipment needed at the mix position. Four slots are provided so up to 32 inputs or 32 outputs can be used, or a combination such as 16 in and 16 out. The control surface is connected to the iDR10 by dual CAT5 cables, one for Ethernet and one for EtherSound. The iDR10 can be up to 100 meters from the surface with copper cable but if longer distances are required an optical solution can be used and redundancy can also be implemented by using standard network solutions approved for EtherSound. The EtherSound link also carries the PFL and talkback signals between the control surface and the mix rack.

Of course, if you don’t need a full blown control surface, then an Allen & Heath PL-Anet controller from the install range can be used to control the iDR10 Mix-rack. These controllers can be used to provide local control on stage with musicians controlling their own monitor mix for example, or used in a house of worship to manage the audio system during the week from the pulpit when the choir or praise band are not involved in events.

Finally, the iLive system is packaged in touring grade flight cases to ensure the units are fully protected. The iDR10 rack is held in a shockmounted, welded rack frame and the wheeled case has removable front and rear covers for easy access. The iLive case is a three-part case for best use of space and ease of handling.

To add further to the flexibility of the system, the surface is available in four sizes – iLive-80, 112, 144 and 176. In the digital world of configurability, the analog channel numbering references seem inappropriate, therefore the iLive surface references represent the number of control strips available on the surface that can be used to control a channel, be it an input, mix, or DCA etc. As each fader has four layers, the number of control strips is four times the number of motorized faders.

Allen & Heath is committed to continual improvement and development and a number of software releases and hardware options introducing new features are planned. The nature of the control protocols of the system also allow a number of alternative control systems to be implemented in the future, both over Ethernet and PL-Anet and alternative audio networks.

The benefit of digital is flexibility and the ability to recall settings but those benefits are only of value if they can be easily harnessed. The management and design staff believe that the iLive system presents a digital console that is as easy to drive as an analog one, and is extremely flexible without being intimidating. Visit http://www.ilivedigital. com or http://www.allen-heath.com/us for more information. ■

Glenn Rogers is Managing Director for Allen & Heath.