SR/Live Sun, November 23, 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.