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John Eargle
(Surround Microphone Techniques)

Perhaps best known as the Delos recording engineer responsible for some of the finest recordings of classical music available, John Eargle has also been a long-time advocate of surround for realistic reproduction of music, and explained in his talk, "Surround Microphone Techniques" how he captures and produces a multi-channel recording, illustrating his points with Delos multichannel SACD releases. Audiophile purists who have a naïve view of how recordings are actually produced might not want to read further, as you may learn things about some of your favorite recordings that are unlikely to sit well with your ideological bent.

Click for a Larger Image

Delos surround recordings are produced primarily as a stereo (2-channel) project and are monitored on-site as a 2-channel recording, because 2-channel discs are still so economically important. Surround signals are derived from microphones placed around the hall, but the sounds they capture are not monitored on-site as final signals to be delivered to the surround channels. Instead, John claims that his real challenge is to capture enough material so that he can create a good, believable surround mix in post-production. Raw material for surround is captured as stereo pairs, with up to 8 tracks recorded in total. In addition to surround material, some of those 8 tracks are used to capture difficult subjects, like soloists and choral forces.

John looks for different things in stereo and surround recordings. The stereo recording must have accurate imaging in the sweet spot, conceding that a 2-channel recording has a narrow listening area. The sense of spaciousness must be based on cues that come from the front, and he is very careful not to overdo these cues. Surround expands 2-channel: imaging improves because of a center channel, and surround adds envelopment to the listening experience.

Because John monitors and primarily records in a 2-channel environment, a significant amount of editing is necessary to create the surround version of any given recording. For example, manual steering is effectively used to create the center channel; the signals that will go into the center channel are subtracted from the front left and right channels in order to avoid conflicting imaging cues from the phantom image produced by the front left and right speakers, and the real image from the center channel. Click for a Larger Image

The surround signals are derived from the house pair of microphones that are always present in a hall. Some techniques John uses to process these signals include subtracting the house pair from the fronts to further separate perception of front from back imaging, delaying the surround signals to increase decorrelation and simulating early reflections by mixing some of the front channel signals into the surrounds. John stressed the importance of maintaining the decorrelation of ambience in all channels for as wide a frequency range as possible so that the surround signal will be more difficult to localize. Decorrelated material is easier to use for surround signals and gives the recording mixer more choices and flexibility when producing the surround signals. Decorrelation can be ensured by using several widely spaced microphones or by artificial reverberators, such as those manufactured by Lexicon.

The overriding impression I received from John's talk was that record engineering is very much still an art form, requiring good taste informed by experience and experimentation to produce a recording that, while not objectively accurately capturing the original soundfield, gives a perceptually, subjectively accurate impression of the original performance. Interestingly, with more channels available, recording engineers have to work harder than before to deliver to us a sense of the performance venue, but consequently the results can be far more convincing than ever before. []

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Show report last updated: 7th September 2003.


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