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The intricacies of capturing phase-coherent surround sound by Pieter Schillebeeckx, Product Manager, SoundField at TSL PPL S ince its acquisition of SoundField, TSL Professional Products Ltd, a leading manufacturer of surround microphones, audio monitoring, tally and power management solutions for the broadcast industry, routinely field a growing number of questions from the industry regarding the successful capture and final dissemination of 5.1 audio. Below is a sampling of questions that have come up at recent exhibitions. What is the design concept behind a four capsule microphone delivering 5.1 audio? How can that work? The conceptual design behind all our microphones is based on the tenet that acoustic events can be represented by four, precision-aligned, microphone elements. In what we call our SoundField B-Format, the signals from our four elements are then combined into ‘X’ which is front/ back information or depth; ‘Y’ which is left/right information or width; ‘Z’ which is up/down information or height and ‘W’ the central point from which the other three elements are referenced. Due to this unique process, surround recordings made with SoundField microphones can be collapsed to stereo or mono without the phase cancellation and high frequency differences encountered when summing together signals from multiple spaced microphones used to synthesize a surround field. This phase coherence is especially important for broadcast applications where surround information might be downmixed for internal stereo editing and mixing, upmixed back to 5.1 for broadcast, only to be downmixed to stereo again by a home television set that is not surround capable. Beyond phase coherence, what are the advantages of a surround microphone such as SoundField over multiple microphone placements? First and foremost, a surround signal from a SoundField microphone delivers an extremely realistic ambient atmosphere that accurately reflects any indoor or outdoor space. With the multiple microphone approach, the phase of the ambient content from each individual microphone can fight the overall quality of the signal. Another major advantage is the ability to control the SoundFIeld B Format X, Y, Z and W parameters from an OB van or studio. For example, let’s say a football game is in the fourth quarter and the away team is drastically loosing with no chance of redemption. The away side of the stadium might be considerably quieter, so the sound engineer in the OB van or studio is able to gently re-rotate the ‘Y’ parameter information to attain a better ambient environment without actually moving the microphone. Our microphones capture everything that goes on around the microphone while the engineer controls the different parameters from within 5.1 listening/mixing environments. A SoundField surround signal becomes the sonic glue, if you will, where effects, commentary and music sit in a constant, phase coherent, natural sounding ambient field. What’s more, the set-up and de- rigging of a single microphone is far simpler than having to set up multiple arrays at any given event. What are the differences between your higher-end and lower-end products and what would be the best applications for each? The DSF-B Broadcast package, our high-end solution, is a completely self-contained surround microphone system with control and processing included, whereas the SPS-200 software controlled microphone is suited for those working in the field on laptop based recording systems or in the studio on digital audio workstations.. The SPS200 relies on a console’s mic pres and a post production plug-in for processing on a DAW and provides a solid front-end to capture 5.1 or stereo. The DSF-B Digital Broadcast package is squarely aimed at live broadcast applications, especially for covering outdoor events. We use studio-grade condenser capsules in order to give the microphone high reliability in a wide range of environments. We have also engineered a heating element inside the microphone that will drive out any moisture and keep everything at a constant temperature to guarantee operation in all sorts of different conditions from really high humidity to snow storms. That’s a very important part. In contrast, the SPS-200, is designed for less-vigorous, often indoor recording in a small studio, or for live orchestral or voice-over 54 | TV-BAY MAGAZINE: ISSUE 77 MAY 2013 TV-BAY077MAY13.indd 54 02/05/2013 21:18