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Making surround-sound the Ambisonic way

technofile  by al fasoldt

Columns and commentaries in a life-long dance with technology

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Making surround-sound the Ambisonic way

By Al Fasoldt

Copyright © 1992, The Syracuse Newspapers

An old method of making sound in the round is staging a comeback in the hi-fi business.

It's called Ambisonics (it's spelled with a capital letter because it's a trade name). Europeans have known about Ambisonics for decades, but most American music lovers have never heard of it. This may change in the coming year as Ambisonic surround-sound decoders are introduced by major Japanese electronics companies.

Onkyo, a hi-fi equipment maker, demonstrated its version of an Ambisonic decoder at the recent annual electronics show in Chicago. The decoder is built into a pricey audio-video receiver, the Integra TX-SV909PRO, but the company may make the decoder available in a separate unit also.

The best part, however, is that a surround-sound decoder isn't even needed. Much of the benefit of Ambisonic recording can be heard by playing back an Ambisonic CD-which sell for the same price as standard CDs—on a standard audio system, with two loudspeakers.

I checked that out for myself with a demonstration disc sent by Onkyo. It's called "Ambisonic Surround Sound Sampler" and was produced for Onkyo by Nimbus Records of England. In addition to excerpts from some of the 400 recordings available in Ambisonic sound from Nimbus, the demo CD contains specially recorded test tracks that show off the amazing properties of Ambisonics.

Even on my standard stereo system, without any surround-sound decoders running, I was able to hear music coming from points far beyond the confines of my speakers. Instruments and voices could be clearly heard to the far left and far right, as well as in front of the speakers and behind them.

What was even more impressive was the eerie sound when I turned off the speakers and put on my stereo headphones. When a narrator started walking around the Ambisonic microphone, I was able to hear his voice coming from all sides, including the rear. For headphone listening, this is something extremely rare and uniquely exciting.

In most of the recordings that I'm familiar with, recording engineers use many microphones, sometimes placing a mike in front of each performer. Before the audio signals are sent to the mastering recorder, these microphone signals are mixed together to give what can only be called a pseudo-stereo effect.

Some recordings made by audiophile engineers use only two microphones, usually spaced about 6 feet apart. This provides a much more realistic stereo effect.

But Ambisonic recordings defy both the conventional multi-mike technique and the typical audiophile method. Often, the left and right microphones for Ambisonic recordings are built into the same housing, with their pickup elements only an inch or two apart.

Each one is aimed at an angle to the front and side. Because the mikes are so close, you'd think that the left and right channels would be barely different from each other, but a special signal technique makes sure that the sound heard at your speakers is exceptionally lifelike.

Some Ambisonic recordings use a fancier method involving four microphones, all nested together. The demo disc has tracks recorded by both methods, and each one seems to do a spectacular job.

Onkyo's Ambisonic A-V receiver will be on sale this fall; it's likely to be expensive, at least at first. Nimbus CDs are sold in record stores and by mail. For a catalog of Nimbus recordings, write to Nimbus Records Inc., Box 7427, Charlottesville, VA 22906, or call 804-985-1100.

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