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ELC Audio Engineering
1534 N Dorsey Ln Tempe, AZ 85281



Click HERE (or click on above photo) for the original ELC Audio Engineering home page that included photos, links to articles, and miscellaneous artwork by yours truly.

Click HERE or on photo above for my vacuum tube amplifier bibliography.

The remainder of this page provides links to websites pertaining to Ambisonics and Cochlear Implant research.


My first Ambisonic microphone: Core Sound's TetraMic

The rotating head figure (above) was unashamedly borrowed from Jérôme Daniel's Ambisonics and 3D Research website. His website, doctoral thesis, and highly informative PowerPoint presentation (in French) on high-order Ambisonics can be accessed here: gyronymo.free.fr/index.html

"Ambisonics goes further than stereo in that what it does... is to sample the acoustic field in such a way that the combination of the signals from all the loudspeakers in the array produces… a reconstruction of the original acoustic wave field (both traveling and standing wave components).
If a listener puts their head in the sound field, because the wavefronts are similar to the original, the perception of directionality and space should correspond to the original too. It is a ‘wavefront reconstruction’ scheme in the small. The ear signals (crosstalk and all) will be correct if the reconstructed wavefronts are correct. This is just like natural hearing.
Increasing the number of loudspeakers in Ambisonics (each fed its correctly-decoded signal) increases the accuracy of the reconstruction and the region over which it holds up. The interaural arrival-time differences also correspond to natural hearing in Ambisonics.”
ambisonic.net quoting Professor Stanley Lipshitz]

I will be adding a comprehensive bibliography on Ambisonics, to include direct web links to articles when possible. A number of sites are quite good, but I avoid providing direct links to sites that have pop-up ads (the ads may be benign, but I don't want to alienate anyone because of dubious ads). For readers who are new to Ambisonics, a good place to start is ambisonic.net (noting that it's ambisonic, not ambisonics). My goal is to demonstrate how Ambisonics is an appropriate technology for researching the effects of noise using normal- and hearing-impaired listeners. Controlled, real-world listening tests will enhance the external validity of research and claims regarding hearing aids, cochlear implants, and assistive communication devices.

Another highly recommended source of information on Ambisonics is the Audio Engineering Society (aes.org), particularly their anthologies on Spatial Sound Techniques (Parts I and II). I am currently reviewing a number of web sites regarding Ambisonics in addition to reading a long list of journal articles on 3D recording and playback techniques.

I have observed that a number of authors attempt to explain Ambisonics terms. Their explanations generally make it clear that the Ambisonic W, X, Y, and Z signals are NOT speaker feeds (i.e., they're not the same as the signals ultimately routed to the loudspeakers). What most authors fail to explain, however, is that the W, X, Y, and Z signals aren't the signals originating at the microphone capsules either. If one attempts to make Ambisonics recordings using separate microphones (versus, for example, the Soundfield mic), the unprocessed microphone signals, as with the speaker feeds, are not the same as the ubiquitous Ambisonic W, X, Y, and Z signals.

Ambisonic B-format signals are not speaker feeds. Neither are these power lines (egad!).

Brief note regarding Ambisonic microphone techniques: Michael Gerzon, Peter Craven et al expanded upon the stereo concepts pioneered by Alan Blumlein to develop the concept of a microphone system that could reproduce a full three-dimensional soundfield. Both Blumlein and Gerzon realized that only when a sound wave is captured at a single point in space can it be reproduced faithfully and without the phase distortion anomalies inherent in spaced microphone techniques. Microphones designed for first-order Ambisonic recordings use four carefully-matched (sub)cardiod microphone elements situated on a tetrahedral mount. The Soundfield DSF-1 is one such microphone, as is the Core Sound TetraMic. Higher-order recordings can be made using mh acoustics' 32-element em32 Eigenmike® microphone array.

Keith Howard's audiosignal.co.uk website is a nice resource for Michael Gerzon's early writings on audio-related topics. This resource includes articles that appeared in Hi-Fi News, Studio Sound, and Wireless World (please note that a lot of these articles are not related to Ambisonics). Keith Howard's "Gerzon archive" can be accessed directly here: Gerzon archive.


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