When Robert Schumann visited the decade-old grave of Franz Schubert, it was not in its current place of honor in Vienna’s Central Cemetery, but rather in an outlying location. Walking back to his lodgings, Schumann, strictly on a whim, knocked at the door of Schubert’s brother Ferdinand and made the greatest discovery in music history. Hidden within the lodging was the score to a much longer than normal symphony of Schubert’s, what we now know as the “Great” C Major. Schumann brought his treasure to his friend Mendelssohn, who mounted it in the next year of 1839.

What must it have sounded like at its premiere? At the Rose Theater as part of the Mostly Mozart Festival, the Orchestra of the 18th Century provided some clues. This unique ensemble was founded by recorder player and conductor Frans Brüggen in 1981 and populated with experts on early instrument performance practice. Its 50 members hail from 23 countries, and the group has not appeared in America for over 10 years.

We have been missing a lot. This assemblage is one of the world’s most impressive, and graced this concert with an exceptional pinpoint accuracy and palpable sense of discipline. Mr. Brüggen sits while conducting; his gestures are small but eloquent. What was most remarkable about this realization of the C Major, complete with every possible repeat, was its arresting sound.

With woodwinds actually made of wood and small kettledrums struck with hardheaded sticks, this version often aped one of those magnificent 19th-century works whose inspiration was the field of battle, say the Symphonie funèbre et triomphale of Hector Berlioz. With the reverberant acoustics of the Rose Theater as an accomplice, this performance was extremely memorable.

For sheer quality of play, this type of raucous exuberance is hard to beat. But the discomfort expressed by some of the patrons riding down in the elevator afterward was understandable. The sound for which they longed, the Victorian stuffed sofa of a full symphony orchestra, was decidedly missing. But no- body would have a quarrel with the colorful enunciations of this band, whose emphasis on superb wind communication produced many new sounds, and allowed previously hidden voices to emerge. When they ended a phrase or a movement, they would offer a little crescendo on the final note followed by a bit of a diminuendo, growing louder and then softer at exactly the same time. Few, if any, modern orchestras can boast of such unity.

Equally spectacular, but in a very different manner, was the group’s rendition of Schubert’s most famous symphony, the B Minor. This was quite simply exquisite, a lovely gambol through heavenly material, leaving the impression of great beauty. Too bad they couldn’t have offered the final two movements as well.

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The 2007 Mostly Mozart Festival closed this weekend with a performance of one of his towering works, the immortal Requiem. The choir signed for the occasion, Schola Cantorum de Venezuela, began the Avery Fisher Hall concert with a set of American music from far south of the Mason-Dixon Line.

The Argentinian composer Alberto Ginastera was a major force in the music of the last century, and wrote his Hieremiae Prophetae Lamentations — Lamentations of Jeremiah — during a year of study in New York. The ensemble had difficulty with its diction in the opening O vos omnes, a rapid movement with complex accent patterns, but made a nice recovery in the ecstatic Ego vir videns middle section. This chorus has a pleasant, if not a very robust, aggregate sound.

The most moving work in this a cappella introduction was the Stabat Mater of Alberto Grau, a Spaniard who moved to Latin American and founded this particular singing society. A depiction of the wind through the landscape of the crucifixion expressing the holy mother’s tears, the piece begins with whispers and shudders, reminding of another biblical setting, the burning bush scene in Schoenberg’s Moses und Aron. The words themselves become angular and increasingly discordant. Some well-positioned eloquent silences augment the sacred atmosphere. The people of Venezuela have a great faith. It will sustain them in the dark days ahead under atheistic leadership.

After these Latin efforts, the group switched to Portuguese for a lively reading of Jubiabá by the Brazilian Carlos Alberto Pinto Fonseca, a fantasia on Camdomble themes, themselves a mixture of South American and African rhythms. By now, the chorus had added kinesis to its performance, and swayed and gestured in time to the music and its atavistic and animistic attractions.

Finally, those who had hoped in vain to survive an hour of Latin American music without percussion must have been crestfallen when the singers whipped out maracas, gourds, and cowbells for La Fiesta de San Juan by Beatriz Bilbao, a student of Mr. Grau. This offering, in Spanish, turned out to be a rather gimmicky modernist pastiche, but it did give the chorus members a chance to dance and gesticulate in a savvy maneuver of misdirection that took the listener’s mind off of the elementary quality of the music.

Only a few notes of the Mozart, though, were needed to underscore how hopelessly underpowered the group was for a work of such scope and depth. Receiving no assistance whatsoever from the desiccated acoustics of the auditorium, the singers simply couldn’t keep up. Their day of wrath sounded more like a fit of pique.

They were, sadly, a good fit for maestro Louis Langrée and the Mostly Mozart orchestra, who, as has been their pattern during this festival, played reasonably accurately, but with little passion or fire. What was missing was the bite of this normally sharply accented music. Mr. Langrée seems to want to homogenize everything, producing a continuous sound that screams out “Hey, I’m not so bad!” But Mozart demands so much more.

The soloists were all good, if a tad uninspired. Having heard him several times at the Metropolitan, I was a bit peeved at bass Morris Robinson for not letting it all hang out in the Tuba mirum. Similarly, soprano Isabel Bayrakdarian and mezzo Kelley O’Connor were fine as far as they went, but perhaps were underwhelmed by Mr. Langrée’s easy listening approach. Only tenor Matthew Polenzani was glorious, floating free above the fray with remarkable resonance.

So another Mostly Mozart Festival has come and gone. What have we learned? Visiting orchestras tend to be superior to the local band. Any music can be considered classical if the marketing department works hard enough. Donning a white jacket makes a musician a bit too relaxed. And, oh yes, and some more investment in Mozart might be nice.