Benefits of a SoundField System
How does it work?
On first hearing what SoundField mics can do, many experienced engineers have expressed disbelief, but while the microphone systems are based on some very clever technology, it is possible to explain how they work in simple, readily comprehensible terms. All SoundField systems are based around a patented multi-capsule microphone and a decoding processor, the design of which has been continually refined as both capsule manufacturing techniques and electronic components have improved. A range of decoders is now available, from easy-to-use hardware processors designed to work in stereo or mono up to DAW-compatible software which can decode to a variety of surround formats. The microphone contains four sub-cardioid capsules mounted in a tetrahedral arrangement, and when the output from these is decoded by the associated processor, a four-channel signal is created, known as the SoundField B-Format. Three of the signals, the X, Y and Z channels, describe the space around the microphone in the X (Front/Back), Y (Left/Right) and Z (Up/Down) dimensions, and are equivalent to recordings made with three figure-of-eight microphones at right angles to each other. The fourth channel, known as W, is equivalent to a recording made with an omnidirectional microphone, and provides a reference for the three other channels.
Download B-Format information sheet (PDF - 449 KB)
It's the B-Format that really sets SoundField apart from its competitors. Engineers familiar with stereo recording techniques will be aware of the phase problems that can result when combining signals from spaced microphones; the further the mics are placed apart, the worse such problems can be. The ideal solution, which results in perfectly time-aligned, phase-coherent signals, is to make multi-microphone recordings from exactly the same point in space, but of course this is physically impossible, as multiple mics cannot occupy exactly the same position. The SoundField microphone gets as near as it can to this ideal by placing the four capsules as closely together as possible in the mic housing. Then, because the distance of the four capsules from the centre of the tetrahedral array is small, known and constant, it is possible to calculate a means of electronically 'correcting' the output of each of the capsules, creating the signal that would be obtained if each of the capsules were mounted at the exact centre of the array. The four channels of the resultant B-Format audio thus describe the complete three-dimensional soundfield around the microphone as captured from an ideal point in space, and their phase coherence allows them to be further processed in combination without any of the time-alignment problems associated with signals from multi-mic arrays.
Once the four-channel B-Format signal has been generated, it is possible to further decode it to a variety of commonly used audio formats. The exact options vary depending on which SoundField decoding hardware or software is used with the microphone, but mono, stereo, stereo M/S, and a variety of surround formats are all possible, including 5.1, 6.1 and 7.1. Best of all, if the B-Format signal is recorded to a four-channel storage medium, the decoding can take place in post-production by passing the recorded B-Format signal through the required decoder, with the decision about the eventual output format being postponed until it is required. This makes the B-Format an excellent 'future-proof' audio archiving format, as B-Format signals could easily be decoded into other surround and 3D audio formats if these take off in the future.
SoundField microphones offer many user options that can seem at first completely impossible even to experienced engineers, and again, these options are available because of the phase-coherent nature of the four signals that make up the B-Format. By combining the individual B-Format channels in different amounts, users can recreate the effect of having made their recording with a mic pointing in any direction - but without moving the mic at all. For example, imagine combining the Y (Left/Right) channel equally with the X (Front/Back) one; the output is the same as would be produced by a mic pointing 45 degrees to one side. Adding some of the Z (Up/Down) channel has the effect of tipping the microphone up slightly, but without physically shifting the mic at all. What's more, combining the X, Y and Z figure-of-eight channels with the W (omnidirectional) channel in different ratios creates the effect of the recording having been made using a microphone with any of the common pickup patterns, from omnidirectional through cardioid, hypercardioid and figure of eight. Once again, all of this can be done after the recording if required, although easy-to-use controls for altering the virtual orientation and pickup pattern of the microphone are included on the front panels of many of SoundField's hardware decoders for 'live' use.
So if these mics are so revolutionary, why isn't everyone using them? After all, the theory behind the SoundField B-Format has been around for a while. It's another over-used promotional phrase, but we consider this technology to have been truly ahead of its time. SoundField mics have made a creditable reputation for themselves since the 1980s as high-quality microphones for stereo and classical recording. But decoding the B-Format live to stereo is only using a fraction of the potential of these systems - and of course, there are more affordable ways of recording in stereo. Today, however, there's a growing need for a simple means of recording 5.1 audio, and SoundField systems meet that need simply and affordably. Already, broadcasts from the 2006 Soccer World Cup and UK Premiership League games have used single SoundField mics to generate simultaneously decoded stereo and 5.1 audio for SD and HD transmission, and SoundField systems have been permanently installed at many large football stadiums in the UK. It's no exaggeration to say that the time is right for SoundField technology as never before.
