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What is a Soundfield Microphone? – For Total Versatility!

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.

Surround Sound System

Suggested configuration for 5.1 surround sound system / Photo by Kamina / CC BY-SA 3.0

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.

A-Format

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.

The A-Format is the signals from four microphones on the faces of a tetrahedron

Depending on the microphone model, this transformation process can be performed in either the hardware or software version of the signal processor.

B-Format

This is the standard audio format that will be produced by a Soundfield kit. It consists of the following four signals:

  • – 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.

Surround Sound System

Diagram of the positions of speakers in a 16.2 surround sound system

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!

Farhan

When I'm not rocking out to great music, I'd prefer to be sleeping on a field on a windy day =)

4 Comments

  1. Great post Farhan. I had no idea there was so much know about all this. In my day we pretty much only had directional mikes and very simple speakers.

    You post is very well organized. It is informative and the art work is very well suited to the material. I know more than I did because of you content and that is the goal.

    Great job. Keep up the good work.

    • Hi Frank!

      Thanks for sharing your thoughts. It really means a lot to me to know that my articles are educational and easy to read. I look forward to seeing you around here again =)

      Keep in touch!

  2. Very educational. I will definitely spread the word about your website. I am a big fan of music, especially metal and some rock (I assume you are a fan of metal too since you have a metal guitars and amps banner) and i will use your website as a blueprint for resources about audio and music production!
    Once again, great info!

    • Hey Miroslav!

      Really appreciate the support man. Yeah, I too am a metal/rock fan, but am open to other genres of music as well. My job requires me to be versatile in terms of musical tastes anyway, so yeah. You will always be welcomed here on my website, so do visit again soon!

      Thanks a lot!

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