Practical Ambisonics

A Summary of my Experience

I first made an ambisonic recording of a concert in March of 2006.  Now that I have recorded a number of concerts ambisonically, I have written down what I do for the benefit or criticism of others as appropriate.  Some of the details are just ways of working with the tools I have available that are not really multichannel tools.

The hardware I used for recording ambisonics over the first eighteen months was a "native" B-format microphone assembled from AKG Blue Line units (because they were the best I could afford), and a MOTU Traveler interface (in particular, because it has digitally set mic preamp gains). 

I now have a Core Sound Tetramic, which is a cheap alternative to the mics made by Soundfield, but claiming to be as good as them in most respects, and better in some.  The MOTU is still the input device.  The Tetramic is able to be cheap partly because it has no dedicated hardware for processing the capsule outputs and producing B-format signals; instead, the capsule outputs are recorded (A-format), and a program (a customised version of VVMic, or a beta of a VST version of the A to B-format processing) is used to generate the B-format signals from them, with the help of the microphone's individual calibration file.

In no way competing with either of these microphone arrangements, I am also playing with a Zoom H2.  This modestly price recorder can record four surround channels from four built-in microphones, and I am experimenting with generating horizontal B-format from the recordings.

In addition to the Tetramic software, my main software tools for recording and processing are AudioMulch, Plogue Bidule, WaveLab, VVMic*, and Surcode DTS-CD, together with a number of VST plugins: PPMulator, VVMic VST*, A0 Parametric Equaliser*, and SIR*.  The items marked with * are free, but the others I had to pay for.

With this equipment, I can make a B-format recording as .AMB files, and produce, to give to other people, both UHJ-encoded CDs for straightforward stereo playback and DTS-encoded CDs for surround playback on conventional home theatre systems.

My processing of the native B-format microphone assembly included aligning the microphone sensitivities and frequency responses, and I am providing a section with details of how I went about this.  The Tetramic comes with the necessary software a calibration file, so I have a simpler workflow now.  I have a Plogue Bidule setup for converting the H2 surround files to B-format.

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