Have you ever heard of a microphone that can be used to capture sound from all directions? Sounds too good to be true? Well, let me tell you that the technology is already here, and have been around for quite some time. If you want to expand your knowledge on audio technology, then you must find out what is a Soundfield Microphone!
This special type of microphone that we will be discussing about today, is not really a very popular one. In fact, very few people that I know have heard about it, much less understand how it works. Hence, we will look into the unique functions of the Soundfield mic and see how it can be a benefit in various recording situations. Let start learning!
Soundfield Microphone – Captures Everything?
The Soundfield microphone is designed to have four subcardioid or cardioid (unidirectional) microphone capsules arranged closely together in a tetrahedron. Invented by Michael Gerzon and Peter Craven, this microphone is a part of Ambisonics (a surround sound technology). It allows for mono, stereo or surround sound recordings and can also include height information.
How It All Began
The theoretical design for the Soundfield microphone (created by Michael Gerzon and Peter Craven), was developed into a practical microphone system by Calrec Audio Limited. The first Soundfield mic was then launched by the same company in 1978.
However, in 1993, the part of Calrec that was responsible for the Soundfield microphone, separated from the company and became SoundField Limited. They then continued working towards developing and expanding the range of products. After the original patents relating to the soundfield mic expired, other companies have also started to produce soundfield mics.
How It Works
A complete Soundfield microphone kit will include the microphone itself and a signal processor. Two distinct sets of audio signals called A-Format and B-Format will be produced. The sound processor may be in the form of a dedicated hardware, or a computer-based software. The software processing can be done in real-time during the recording, or post-recording.
This is the first set of audio signals that will be produced by the Soundfield microphone itself. It consists of signals produced by all four of the microphone’s capsules. These four signals will typically have to go through further processing before they are used. The A-Format will usually be transformed into the second set of audio signals, which is the B-Format.
Depending on the microphone model, this transformation process can be performed in either the hardware or software version of the signal processor.
This is the standard audio format that will be produced by a Soundfield kit. It consists of the following four signals:
- W – A pressure signal corresponding to the output from an omnidirectional microphone
- X – The front-to-back directional information, a forward-pointing velocity or “figure-of-eight” microphone
- Y – The left-to-right directional information, a leftward-pointing “figure-of-eight” microphone
- Z – The up-to-down directional information, an upward-pointing “figure-of-eight” microphone
The letters “W, X, Y and Z” that you see above, actually represents the terms in the multipole expansion of a function on the sphere. Simply put, it approximates the wave field on a sphere around the microphone. A three-dimensional soundfield can definitely be produced, but the soundfield microphone particularly shows its versatility in a stereo or mono application.
By using software such as SoundField’s Surround Zone, it is possible to combine the signals in various proportions and produce any number of microphones pointing in any direction, before and after recording. For instance, provided the W, X, Y and Z signals are recorded separately, you can pinpoint the microphone to a certain response from the audience even after recording.
To put it simply, the B-format audio signals can be decoded to reproduce any number of microphones pointing in arbitrary directions. Furthermore, the software allows you to change each of the microphone’s polar pattern to be omnidirectional, cardioid, hypercardioid, figure-of-eight, or anything in between. This can be performed while recording or at a later time.
Playback and Limitations
The Soundfield system’s playback configuration is also equally flexible. Similarly, you can make adjustments during the post-production process, and the B-format recording can be decoded to any number of speakers arranged in both the horizontal and vertical planes.
However, do take note that this information can only be manipulated to reproduce the direction of sound at the microphone (this type of microphone response can be synthesized), but it does not allow the reconstruction of what a microphone at a different point in space would record. To do that, the wave field must be reconstructed in more detail (wave field synthesis).
That’s about it for today’s article. Have you heard any surround sound recordings before? Do you think you would benefit a lot from having such a microphone?
Let me know your thoughts down below and share this article with your friends!