Charles Babbage’s mechanical ‘Analytical Engine’, designed in 1833, is regarded as one of the first computing devices. A century later, using electro-magnetic and vacuum tube technology, the massive, iconic, electronic computing machines appeared, easily filling a large hall. After the invention of the transistor, with innovative companies starting to combine them into large scale integrated circuits in the late 1970s, the ‘micro computer’ took off. With Apple and IBM as innovators, these drastically changed the world we live in. In their slipstream, musical instrument and professional audio manufacturers followed by including microprocessors to produce ‘digital audio’ products, eventually rendering most analogue technology obsolete. The big market transition of analogue mixing consoles to digital ones happened at the turn of the century.

For a large scale digital live mixing console, massive Digital Signal Processing (DSP) power is required to perform the calculations needed to run the many input channel strips, mix buses and effects. Although the microprocessors found in today’s high-end laptops and even tablets can provide this power, because of their processing structure they may not be able to do it with a low enough latency. Therefore these ‘native’ audio processing platforms are primarily used in the recording field, where latency is not a show-stopper.

For live mixing, however, low latency is mandatory, so dedicated audio DSP chips are used to provide parallel processing structures capable of performing massive calculations much faster then a native microprocessor could. If you open up a modern digital live mixing console, you will find a combination of the world’s main manufacturers of dedicated audio DSPs: Yamaha, Motorola, Texas Instruments and Analog Devices. Additionally, Field Programmable Gate Arrays - FPGA’s - are used.

Basically, a digital live mixing console can do everything that an analogue mixer can do, but on a much larger scale. This is, firstly, because the DSP power allows for a virtually limitless scope of audio processing; it can support a larger number of equalisers, dynamics, mix buses and effects then an analogue console could ever manage.

Secondly, to operate it successfully the mixing console’s control surface has to be within reach of a human being’s arms and field of view. This means there are a limited number of knobs and faders that can be offered as the console’s ‘user interface’. With an analogue mixing console, each function has to have its own control component - a knob, switch or fader - dedicated for each channel and bus, filling up the control surface until additional control components would move beyond the operator’s reach and view.

Digital live mixing consoles offer control components that can be used in more then one way - for example a row of motorised faders that can operate multiple layers of channels, or an LCD display and ‘selected channel’ tactile control components that provide access to a single channel or mix bus, with channel selector buttons to select one channel at a time. By ‘layering’ the user interface in this way, many more mixing functions can be made available then would ever be possible through analogue knobs and faders.

Finally, even if digital mixing consoles don’t use microprocessors for audio, they will use them for control, which means that they have a memory area where settings can be stored into multiple scenes, to be recalled by pressing a button. In contrast, even the largest analogue live mixing consoles from the past had only one memory. What you saw is what you got, and the only way to recall a mix was to prepare a second mixing console, and then switch the multi-cable.

Where the DSP capacity and hardware audio quality (linearity, dynamic range) were the constraining factors of digital mixers in previous decades, nowadays DSP chips, i/o infrastructure and A/D circuits are so powerful and cost-effective that mixing capacity, i/o capacity and hardware audio quality are no longer limiting factors. As a result, the primary cost of a digital mixing console no longer lies in the hardware, but has moved to sound algorithm software and user interface design.

DSP chips themselves don't affect the sound in any way, it’s the algorithms that make the sound, and this is where the innovation is happening today. More complex and better sounding algorithms are developed, offering higher sound quality then ever before. This development includes new processing concepts - such as complex IIR filters and dynamics, FIR filters and automixing algorithms - and also the emulation of ‘vintage’ analogue circuits with an accepted and loved sound signature. Examples of this are the Virtual Circuit Modelling ‘VCM’ Rupert Neve Design equalisers, dynamics and even pre-amplifiers and input transformers in Yamaha QL, CL and RIVAGE consoles.

Equally important, however, is the user interface, which makes the huge range of DSP functions available to the operator. The more functionality a digital live mixing console offers, the more challenging it becomes for the sound engineer to control and manage it all. Also, the way an algorithm is presented - e.g. the visual design of an equalizer graph on an LCD touch panel - has a huge effect on how the sound engineer uses it. In other words, the user interface is part of the sound algorithm. Supporting a good overview with an efficient workflow to get to the details of a channel strip fast and accurately, as well as supporting creative decision-making in a chaotic live concert environment through a carefully designed user interface, are the key things to look for when selecting a digital mixing console.