Since board member James Meckley has been involved in live recording, maybe he can provide some thoughts here.
I haven't yet heard the Zinman M9 so I'm not in a position to compare it with earlier releases in this series, but that won't stop me from making some general observations. The earlier Zinman Mahler discs I own were all created by the same team: Chris Hazell, producer; and Simon Eadon, engineer. Assuming they also did this M9 (someone might check), they would have been able to reproduce their earlier results
exactly if they had wanted to—their recording logs would contain very precise mic placement and level data. If the woodwinds are indeed more recessed in M9 than in M6, you can be certain that it was a deliberate artistic decision on the part of Hazell or Zinman (If you want to see how much say the producer has in these matters, just watch some of the interactions between Culshaw and Solti in Decca's
The Golden Ring DVD).
My general impression of the Zinman Mahler cycle is that they've taken advantage of the Tonhalle's rather spacious acoustics to make some very natural-sounding recordings with more room sound than is common today. I agree with Todd in preferring this approach when it's done well.
I tried to get some mic-placement insights by reviewing the
Going Against Fate DVD associated with Zinman's M6, but the lighting designer seems to have been unduly influenced by the paintings of Caravaggio—inky-black shadows and single-light-source chiaroscuro throughout—not a microphone to be seen.
As to general mic placement considerations, the stereo pair that Wade described, 1/4 of the way back into the hall and 1/3 of the way down from the ceiling, is typically there for the orchestra's own archival recordings or perhaps for local radio broadcast. With the right choice of mic patterns, this placement can produce a very natural-sounding recording that accurately preserves the instrumental balances heard in the hall. Horenstein's famous 1959 M8 was recorded this way, with just one coincident pair of figure-of-eight microphones in Blumlein configuration. I've occasionally used this basic approach, slightly closer than described, with gratifying results.
A more conventional (and more commercially viable) approach to stereo involves having the primary pair somewhat closer to the orchestra, with additional spot mics added to bring out inner detail. The primary pair, which accounts for 90 to 95 percent of the sound of the recording, is typically located six to eight feet behind the conductor and eight or so feet above his head. Getting this pair in the right place is the most important part of a set up. Moving away from the orchestra increases hall ambiance; moving toward the orchestra decreases it. Accent or spot mics are then added as necessary to bring out detail: typically left and right string mics; a woodwind pair; and percussion or specialty mics as dictated by the specific piece. This is where the skill and taste of the engineer come into play: the goal is to make your eight or ten-mic recording sound like it was made with only two mics—always the ideal. High quality digital delay makes this much easier now than in the early decades of stereo, allowing the signals from all the spot mics to be precisely time-aligned with the signals from the primary pair, thus preserving the integrity of the sonic image.
James