On a rainy afternoon, Michael Shofar sits at the keyboard of the newly installed Holtkamp organ in the Peabody Institute's North Hall and plays a little Bach with his left hand. His fingers caress the wooden keys--rich plumwood for the equivalent of the white keys on a piano; darker palisander, a hard rosewood, for the black.

This is no concert. A small toolbox rests on the bench next to him, and a miniature anvil is clamped to the left of the three keyboards. Sixteen hours a day, for nearly a month, Shofar has been teaching the complex technology of the organ to sing.

There are more than 3,000 pipes in the Holtkamp instrument, each of which must be adjusted to blend in pitch and volume. Michael Shofar has spent four months fine tuning the organ for its home in North Hall.

There are more than 3,000 pipes in the organ, says Shofar, and he must adjust each one to blend in pitch and volume with all the others, a process called "voicing." Shofar has already completed one round of voicing in the Cleveland factory of the Holtkamp Organ Company, where the Peabody instrument was built, "to get the right speech out of the pipe." But now he must go through the entire process again, fine tuning the organ's sound and adapting it to the specific acoustic geometry of North Hall.

"The room sounds good for an organ," says Shofar. "For a piano, I don't know." But then, pianos aren't Shofar's concern.

Shofar's assistant, Don Benninghoff, clambers carefully down a tall wooden ladder to hand Shofar a small pipe from the vast innards of the organ. A few pipes are made of wood--pine or mahogany--but most are formed of tin and lead, alloyed in varying proportions. Some loom big as cannon barrels; others are no larger than soda straws. The tiniest pipes are barely within the human range of hearing and are the hardest to tune, says Shofar.

Benninghoff hands him an oboe pipe about as thick as your little finger. Instead of the simple tube that makes up the other pipes, oboe pipes have a small brass reed that vibrates to create their sound.

"I'm going to curve it a little into the pipe. It's a little too loud," says Shofar. He inches a wedge out, releasing the metal reed, which he places on the anvil. He runs the conical point of a brass rod along the 3-inch reed, bending it up the way a strip of paper curls when you run a straight-edge across it. Shofar replaces the reed and the wedge in the pipe, and Benninghoff loads it back into the heart of the organ. Now Shofar tests it again with another riff from Bach.

Shofar, who has been voicing organs for Holtkamp for 41 years, can change the volume on an individual pipe by opening or closing the small space in the "windway," the opening about one-third of the way up the tube. He pinches the edges of the slot together to dampen the sound or shaves away part of the opening to increase the volume. To modify pitch, he slides a collar up or down at the top of the pipe to deepen or raise its tone. There is a limit to these changes: pull the collar up too far and the sound starts to get fuzzy.

Organ teacher Donald Sutherland will demonstrate the prowess of the new instrument to a Peabody audience in four concerts scheduled for Saturday and Sunday; its formal dedication will be in the fall. "This organ will enrich the entire musical life of the community," says Sutherland. "There is no instrument quite like this one anywhere else in Baltimore."

"It's all a matter of listening to it," shrugs Shofar, as if that explains the whole process. "You spend a lot of time just listening to the organ, adjusting it to the building so one pipe isn't too loud or too soft."

"You design an organ for a specific space," agrees Donald Sutherland, who teaches organ at Peabody. "The Holtkamp fits North Hall both visually and aurally."

North Hall is long and narrow, with high ceilings, below which runs a plaster copy of the frieze that once surmounted the Parthenon in Athens. The walls are painted olive green, and one of Peabody's two 16th-century Flemish tapestries will be hung at the end of summer.

The organ's pipes are arrayed in what looks like the facade of a neo-classical building: a 26-foot-high structure called the case. The main parts of the case correspond to the top, center and bottom keyboards of the organ, notes Sutherland.

"An organ is both a very basic and a very complicated machine," he says. "The mechanical parts all have musical reasons for being there. There's a mechanical feel to playing heavy sounds, so that the instrument helps you play the music."

After weeks of Shofar's voicing, Peabody's new Holtkamp organ will speak for the first time on March 7 and 8, before a Peabody audience. Sutherland, who has waited 23 years for this instrument, will play it in two concerts each day.

"This organ," says Sutherland, "will enrich the entire musical life of the community. There is no instrument quite like this one anywhere else in Baltimore."

Most of the $668,000 cost of the new Holtkamp was borne by a $600,000 gift from Lyman and Nancy Woodson Spire of Syracuse, N.Y.

"This instrument will let conservatory students listen to great works played on a great instrument," says Sutherland. "Composition students will have a new instrument to write for. Singers will have a new accompanist."

In North Hall, Don Benninghoff and Michael Shofar take a break from voicing the organ. A rainstorm rattles against the tall windows overlooking Mt. Vernon Place. They've been at it for weeks, but they can't compete with nature. With a smile and a shrug, Benninghoff says, "You can't tune an organ between raindrops."

All four recitals have been filled, but those without reservations are welcome to turn up in the hope of obtaining a "no show" ticket. An open house and an organ weekend are planned for fall.