Just as its air compressors are finally back in operation, the mighty pipe organ of St. Paul Cathedral will face a different sort of pressure this week.

In the audience for a pair of organ re-inauguration concerts -- following nearly a year of extensive repairs -- will be the expert ears of the members of the Conference of Roman Catholic Cathedral Musicians. The group is in town for its annual national meeting.

The Oakland Cathedral's director of music and lead organist Don Fellows is nervous, but he also can't wait to show off the restoration work done by Taylor & Boody Organ Builders of Staunton, Va.

"Everything is tip-top perfect," he says. "It is quite a different instrument to play since it now all works."

Installed in 1962, the Beckerath pipe organ is one of Western Pennsylvania's largest, with 67 stops, 97 ranks and more than 5,000 pipes. But by last year, much of it had fallen into disrepair, with many pipes not functioning at all. The Cathedral shut it down after Easter for the nearly $1 million restoration process. The instrument was partially brought back online at Christmas, but the final work is being done this week (a few of the lesser-used ranks may be installed after the concerts).

"Everything is perfectly in tune and they have strengthened the case, so the organ sounds more prominent and present, and it plays more precisely," says Fellows. "You can hear details and variety you couldn't hear before. We couldn't have asked for more."

The free re-inauguration events take place at 7:30 p.m. tomorrow in a recital by James David Christie of Oberlin Conservatory and the Boston Symphony. The program includes works by Buttstett, Bohm, Langlais and Guilmant.

The celebration continues at 7:30 p.m. Wednesday in a concert with the St. Paul Cathedral Choir and organists Ken Danchik, Russ Weismann, and Fellows. It features Vierne's "Messe Solenelle" and works by Bach, Karg-Elert, Mathews, Mathias and more. For more information: 412-621-6082.