Stereo in live sound has always been a concept honoured in name only. On PA systems of any reasonable size, in just about every performance space, no engineer is really mixing in stereo. The reasons are pretty simple – if you fully utilised the stereo sound stage available to you as an engineer, it would sound terrible to most of the audience. Only the people right between the speakers in the middle of the room get the effect. Everyone else gets to hear whatever’s coming out of the loudspeaker closest to them. So, we’ve always mixed in a kind of ‘enhanced mono’, putting most sources like drums and bass dead centre, with a little width on instruments like keyboards and guitars, but not too much.
Enter the spatial audio revolution. While ‘surround sound’ as a concept has existed for years and is used every day in cinemas and some theatrical productions, it has the same problem as stereo – it’s an effect that only is truly heard by audience sitting in the centre of the speaker coverage area. Where spatial audio differs is that it uses a huge amount of DSP to position audio sources within a sound field that is perceived as sounding the same in almost all of the room. Effectively, it’s like creating a personal, true stereo mix for each audience member that works in every seat. Some spatial systems go beyond this and create mixes that don’t just have depth and width, but also height.
There’s currently two broad types of spatial audio technology. The first is designed to create a believable three dimensional soundstage using loudspeakers positioned along the front of a stage, pointing at the audience, much like a traditional stereo or left-centre-right PA, but with more elements. This style is designed for the concert and touring market. The second is designed to simulate an acoustic space, or create a completely artificial one, by using loudspeakers that surround the audience, including flown overhead in some cases. This application is mainly for installations, or one-off artistic events, as it obviously uses a lot more loudspeakers.
So how does it work?
Tricking an audience member’s brain into believing that a sound is coming from a specific place, or is being heard in a specific acoustic, is a matter of level, delay, reverb, and filtering, and the complex mathematics of where to send the results of that processing given the loudspeakers available. The ‘touring’ implementation of spatial with seven or more loudspeaker arrays across the front of a stage will typically have a given source coming out of all of them, with varying amounts of delay and attenuation applied according to where the mix engineer has decided to ‘place’ the image of that instrument in the soundfield. The ‘install’ or acoustic simulation will be even more complicated again, with reverberation and filtering added, as well as placement in a field of what could be hundreds of loudspeakers.
The Creative Possibilities
The first goal of most spatial audio systems is to recreate an acoustic equivalent of what the audience member is seeing, and match what the ear hears to what the eye sees. This isn’t currently the case in most stereo or Left-Centre-Right Systems. Even when sitting in ‘the sweet spot’, the brain is usually aware that the sound it is hearing is coming from loudspeakers flown next to the stage, and not from the performers. Most spatial audio systems have a graphic user interface that allows the engineer to position sources visually across a simulation of the space, dragging and dropping (and in some cases widening or lengthening) the source to where they want it to appear to come from. Some spatial systems have this functionality available in the surface control of some brands of digital mixer, with DiGiCo and AVID leading the market. There are also plug-ins available to integrate them with DAWs, mainly for playback.
If a spatial system can be used to position a source in acoustic space, then it can also move that source around in real time. The application for sound effects is obvious – an aeroplane can be heard to fly over the audience, and integration with popular theatrical automation systems like QLab make this pretty straightforward. Some spatial systems accept OSC (Open Sound Control), meaning you can install simple OSC programmes on the average smartphone, and control your sources from there. Innovative English composer and performer Imogen Heap is already using OSC control of spatial audio in her performances, using gestural control built into gloves to send her voice and other sources flying around the space with a wave of her hands.
Where it gets really interesting is in integration with tracking technology like BlackTrax (which uses infrared light) or Zactrack (which uses radio frequencies) to follow a performer around the stage. These technologies are already used with moving lights, and the control signals they output can easily be sent to a spatial system to achieve exactly the same result with audio. In a large scale application like an outdoor opera performance, this level of automated tracking is perfect for recreating the acoustic response of an opera house in open air.
Two major PA companies who are relative newcomers to the spatial audio field are fighting for early dominance, both in the touring and live market, but just as vigorously for installation. L-Acoustics L-ISA system and d&b audiotechnik’s Soundscape are already being used on major tours and in installations worldwide, and are both receiving critical acclaim from touring engineers and venue staff. On the face of it, both systems are somewhat similar, adding a proprietary processor and graphic interface to their existing loudspeaker and amplifier environment, with system design handled using expanded versions of their current design and optimisation software.
Both L-ISA and Soundscape are made to be used with their brand of loudspeakers alone. While both systems have different design requirements, they each offer a frontal ‘touring’ and surround ‘acoustic simulation’ mode. L-Acoustics refer to them as ‘Hyperreal Sound’ and ‘Immersive Hyperreal Sound’ respectively, while d&b use ‘En-Scene’ and ‘En-Space’. Soundscape’s ‘En-Space’ includes models of seven world-renowned performance spaces, and the system uses reverb convolution to replicate their response.
Electroacoustic enhancement systems have been around for decades, with systems like Lexicon’s LARES (Lexicon Acoustic Reinforcement and Enhancement System) first installed into a venue in 1989. These systems were designed to use microphones placed around the performance space and often hundreds of built-in loudspeakers to alter the response of a room during orchestral performances. Their closest modern successor is Meyer Sound’s Constellation system, which is custom designed for each space it is installed into, and offers room enhancement as well as spatial audio capabilities. It has been installed in spaces as diverse as restaurants and corporate meeting auditoriums, as well as concert halls. Like L-ISA and Soundscape, it is only designed to work with Meyer Sound speakers, and Meyer Sound technicians must design and commission it.
There are multiple spatial audio processing options available that stand alone from loudspeaker and amplifier brands, opening up spatial as an affordable option for venues and rental companies with existing inventory, regardless if they have Adamson line arrays or a JBL distributed system.
Astro Spatial Audio from The Netherlands are a leading loudspeaker agnostic brand, with their SARA II processor outputting 128 channels of either MADI or Dante. Simultaneous control can come from Windows, Mac, iOS, Android, DAWs, mixing desks, tracking systems, or OSC, making it an extremely flexible platform. It’s been used in musicals on Broadway and the West End, as well as in live touring and installations.
Barco’s IOSONO also has an impressive list of credits to its name, including Handa Opera on Sydney Harbour, Kraftwerk in London, and a Björk retrospective at MOMA in New York. IOSONO uses wave field synthesis implemented in a ring of loudspeakers that recreates size and shape of the wavefront that would be produced by a real acoustic source. For example, imagine a helicopter was flying past your venue and the soundwaves it created could come through the walls to your audience. The three- dimensional sphere of sound that would naturally project from and move with the helicopter can be recreated by shifting acoustic energy across the multiple loudspeakers, forming a sphere of sound the same size and intensity. IOSONO also features up to 128 channels and MADI connectivity.
We’ve heard both d&b Soundscape and L-Acoustics L-ISA in action, and don’t doubt that spatial audio is the future of live sound. In addition to the advantages of providing realistic imaging, spatial systems remove all of the traditional limitations of mixing to the stereo or LCR bus. Live mixing to large PAs, since its inception, has always been the art of deciding how to change and compromise sources so that they all blend and ‘fit’ into the spectrum and energy available in the PA. To do this, we’ve employed tools and tricks ranging from dramatic EQ, side chain compression, group compression, and our go-to outboard ‘special master bus compressors’ that ‘glue’ our mixes together. Almost all of these techniques and processes become irrelevant when mixing to a spatial system. As spatial systems are deployed more and more frequently for touring acts and major events, FOH engineers are going to have to unlearn and then relearn their trade.
Spatial uses more loudspeakers, but usually smaller and lower powered than what would be employed as part of a left-right system. The result is more headroom in more places, with less demands on the system. Mixing an orchestra on a traditional system is shoehorning the enormous dynamic and frequency range they produce into something that can’t quite handle it, and big orchestral moments always make PAs ‘choke’ a little, changing the natural dynamics and producing a result the brain knows isn’t accurate. Spatial systems don’t have this problem.
The Audience is Listening
Audiences might not be aware of the changes that are taking place in what they’re hearing, but they will very quickly become accustomed to hearing superior sound. At one spatially mixed gig we attended, we asked a nearby audience member who had no technical experience what she thought of the way it sounded. To her, it was ‘seamless’, and it was like ‘there aren’t any speakers at all’. Discerning audiences in the classical and jazz worlds will likely be first to demand the superior results offered by spatial, with the top end of touring to follow. Theatre installations are a given, with only which platform will become dominant remaining to be seen.