SoundField Technology and B-Format

To understand SoundField B-Format Technology, it's best to examine the core issues Michael Gerzon attempted to resolve in creating the SoundField system. Those issues are:

• capturing 3 dimensional acoustical information and "single point source" technology. We'll start with the 3 dimensional capture issues...

What is B-Format anyway?

To understand B-Format, its first necessary to understand that sound is a three-dimensional event. A way to envision the concept of three dimensions is to think of a photograph of a cloud laying flat on a table. You look down on the photograph, and you see depth and width of the cloud, a two dimensional representation of a cloud. While looking at the photo, you know it represents a cloud, but it cannot be confused for a real cloud because we know a real cloud has height as well as depth and width. No matter how good the photo is, no matter how high the resolution, it cannot be confused for the real thing. The missing information required to define the "real" cloud is the third dimensional component- the vertical information.

Now imagine a sculpture of a cloud. It has all 3 dimensional components in evidence-we see depth, width and height. If the sculptor was highly skilled, the sculpture might look like a real cloud sitting on the table. We could probably confuse a really accurate sculpture for a real cloud. The same thing is true in audio, that high resolution, two dimensional audio (stereo) can be very good indeed, but it is not even close to describing the real live event.

The "three dimension" concept can be confirmed with your own ears. When you hear a natural acoustical event, such as a bird singing in a tree, you can almost instantly locate the source as "in front of you, to the left and up there". If you heard the event in only two dimensions, you might know the bird was singing in front of you to the left, but you would not know if it was "up there" or "down there". Without the vertical information, you couldn't be sure exactly where the sound was coming from.

B-Format compares to stereo just as our cloud story does to sight. Instead of defining the world of sound in just two dimensions, B-Format defines it in three. B-Format contains information to define front to back (1 dimension), left to right (2 dimensions) and up and down (three dimensions).

There is one more issue to understand B-Format and three dimensional descriptions of audio events. It's called the "reference". Imagine that you are standing between two trumpets, both being played at the same time. We have sound emanating in all three dimensions from each trumpet, front to back, left to right and up and down, but we have two different "points of origin" of sound. These trumpets are in different locations when compared to our location, which can be thought of as the reference point to these two sounds. To fully describe to someone else the real event of hearing the two trumpets, we need to describe all three dimensions of the sound of each trumpet and the location of the two trumpets compared to where we were standing (the reference). So we really need to describe four elements, the 3 dimensional components of the trumpets and the reference point from which the trumpets were heard. Any attempt to accurately define the real acoustical event of standing between two trumpets playing at the same time in any less than three dimensions, including a central reference point, will fall short of being accurate.

The cloud and trumpet analogy give us a good understanding of the technical value of B-Format and how it works, delivering 4 channels of audio containing the 3 dimensional components plus a reference. A particularly good scientific description of B-Format can be found in Ron Streicher's "The New Stereo Soundbook". Ron discusses all types of microphone methods and recording practices. In chapter 13.11, Ron says: "Gerzon's process focused on the acoustical components of the SoundField at a particular point in space: the absolute sound pressure[the reference] and the three pressure gradients [the three dimensions of sound] that specify the cardinal directions-left/right, fore/aft, and up/down. By accurately preserving these four components, all information needed to recreate that point in the SoundField could be recorded and later reproduced precisely". Click here for a link to Ron Streicher and his book.

To go a little deeper, take a look at the drawing to the right. This drawing shows a graphical representation of SoundField B-Format and how it "looks". B-Format is a sphere, with four elements: an "X" plane (fore and aft or front to back), a "Y" plane (left to right), a "Z" plane (up and down), all with a central reference called "W". B-Format is the core of SoundField Technology and is unequalled for documenting and translating the four elements of real acoustical events so they can be recorded on any 4 channel audio recorder. SoundField Microphones use input processing to convert the raw tetrahedral 4 capsule outputs into B-Format. Using B-Format as the basis for all further processing, X, Y, Z and W components can be manipulated to change any number of parameters, yielding a different microphone pattern, a Mid/Side output, a different "virtual" stereo mike angle (width) or a mono output. The beauty of B-Format and SoundField Microphone Systems is that all output options derived from B-Format are based on the same reference information, so there are no phase difference issues to contend with. This highlights a key feature of SoundField called "single point source" technology.