Holophony; a loosely assembled adjective to describe an audio concept a whole lot more exciting than you might imagine. It’s the word that is being used to describe a production at the Sydney Opera House (SOH), Korngold’s ‘Die tote Stadt,’ The Dead City. The thing is, this opera requires an orchestra that could fill the stalls, yet Sydney Opera House boasts a more modest pit, certainly not one suited to one hundred and forty musicians and choristers, and it’s for this reason we need to understand the true meaning behind this new adjective.
“Holophony is not the correct term but the idea is easily understood; to create an image of sound to replace what isn’t there,” explained Tony David-Cray, sound designer for the project and head of recording and broadcast for the Opera House. The system engaged to deliver this acoustical sleight of hand is a combination of d&b audiotechnik loudspeakers arrayed in a most unconventional format, and a spatial audio algorithm, designed to place virtual sound sources into space so they are perceived as having either stable position or stable direction by everyone in the auditorium.
The issue for David-Cray was one of veracity: if you cannot fit the orchestra in the theatre how do you present a true rendering? The concerns for performers and audience alike are clear; fortunately he was given time to ponder. “Normally with these kinds of productions you hire in a sound designer and it’s business as usual. I’ve been making designs here for a number of years but it was all too apparent to me having to place the orchestra outside the auditorium meant contriving a different approach; this could only be done with contributions from a very different team. Opera Australia approached me about a year ago and it was around this time and by happy coincidence, I bumped into Ralf Zuleeg from d&b audiotechnik who happened to be engaged elsewhere in the Opera House. I mentioned what I was doing and his eyes lit up. He immediately understood what a crazy project this was. I had mentioned it deliberately; his experience with loudspeaker systems and sound reproduction was well known to me, and I knew he was completely up to date with the latest in technology: what I didn’t know was that he was so conversant with this complexity of audio imaging.”
Zuleeg contacted IOSONO at their base in Erfurt, Germany and a team was assembled, with Stephan Mauer now joining Zuleeg and David-Cray on the project. “We also needed equipment support,” added David-Cray, “Shane Bailey from NAS, the d&b Distributor for Australia, came on board; he in turn coordinated sourcing the equipment we’d need.” Again good fortune favoured David-Cray’s project, as Bailey explained, “Yes, NAS pulled together the seventy odd T10s from our stock, the timing just happened to be so that we were able to pull it together from inventory. Lucky timing!” The fifth contributor to the team was the SOH sound department led by Steve McMillan, “They solved the problem of how do we get everything in there, and then successfully run and maintain the system for each performance.”
Zuleeg designed his system based on a single loudspeaker model, “I chose the T10 because it can be used as both line array and point source; it does country and western as I like to say. Because it has the same sound characteristics whatever way you use it, it made my life simple; I wouldn’t be wasting time on the fine tuning of a system composed of different elements, and in both line and point source formats. In the first instance Tony asked for a system that would provide for the audience only, and fold back loudspeakers would be used for the performers on stage. The task was to build a sound system which created an absolutely real sound field; the singers were to perform unamplified so the ratio between them and the orchestra had to work for the entire room”. Between Zuleeg’s system design and Mauer’s application of the spatial audio algorithm to the loudspeaker setup, the sound field that emerged surprised even them when first set up just a week before first night. “At the very first test it was clear when you stood on stage that the performers would have the impression an orchestra was actually in the pit,” said David-Cray. “It sounded so natural in the audience; even when you sit in one of the rows closest to stage, a position where you are perhaps just 1.5 metres from a T10 loudspeaker of the frontfill array, still you are not aware of the loudspeaker, it just sounds completely natural.” The best way to imagine how the system works, explains Mauer, is to recognise that we are not using the loudspeakers to reproduce sound, more they are being used to create the natural sound field of a virtual sound source. The algorithms calculate the driving signals for the relevant loudspeakers that are necessary for the listener to perceive the sound in the perspective where it is meant to be; if you like, listeners are hearing music coming from instruments that aren’t actually there.”
How does this perception of the orchestra’s dimensions manifest itself throughout the auditorium? “It is very consistent,” said David-Cray. “Out in the main room, front to back, side to side, the localisation of the orchestra is amazing. Sit in one position and you hear, for example, the violins and the celli are immediately behind; sit in another and the orientation shift is as if the musicians were actually in place.” There was no mistaking the excitement in David-Cray’s voice; the more he spoke about it, the more compelling his exposition. “It is just as stunning on stage; it’s amazing how the singers on stage pick up cues they hear from the room. I stood with them in the mid-front region of the stage and what you hear is the sound of the orchestra coming from in front but up and out beneath your feet, just as if elements of the orchestra were positioned deep in the back of the pit; it really is quite spooky. Move to the front edge and the impression is even more pronounced, just as it should be. We took the conductor Christian Badea around the room and up on stage and he said the same thing; spooky.”
“I have a gut feeling that this method of audio imaging is something we in the sound fraternity will all be talking about for some time,” continues David-Cray. “It gives you a totally different feel for design. It takes the technology out of the listening experience and brings us back to the more important philosophical question, what is performance? What do I mean by that? Take something easily understood, the cocktail party effect. In a busy sound environment such as a cocktail party, the ear brain system enables you to zone in on one voice whilst at the same time ignore the babble around you. You can do this because the brain can process the signals from our two ears and separate out the angular differences between all the sounds. It’s called binaural unmasking and it is intrinsic to how we perceive the world around us as well as to how we listen to orchestras; the audience member does the mixing in their head. This is where the d&b obsession comes in! The voicing and angular consistency of the loudspeakers, together with the clever algorithms, all support the listener with their ‘suspension of disbelief,’ they might not see the orchestra, but it is good enough that they can believe it is there. That’s what I mean by taking the technology out of listening.”
“The great thing is this is nothing to do with sound people creating a great mix, in truth the sound guys don’t touch the sound; as I explained before it is the conductor who is put in control, it feels that real. Ralf has been a great asset for us on this project; once he brought Mauer on board I began to see this was completely achievable; but I didn’t expect the image to be so potent. It is a different world; this has opened another door. In the end it comes down to reproducing art and in that respect the technology disappears. A completely new world.”