Last week on his blog, Unanswered Question, Joseph Horowitz (co-founder of The Post-Classical Ensemble, among many other claims to fame) posted an open letter to the director of the Corcoran about music in the galleries. During a recent visit, he had encountered a cellist playing Bach suites in the atrium, and he felt that this clashed with his experience of looking at the art.

The NSO is on its way home, having wrapped up the final, Brazilian leg of its South America tour.

Reviews have been generally adulatory. “Eschenbach’s conducting is of an admirable clarity; his gestures are precise,” said the reviewer in El Pais of the NSO’s June 22 concert in Uruguay. My Portuguese is not up to tackling the reviews from Brazil, but anyone who wants to locate them is welcome to post them in the comments section.

Last year, the Royal Opera House Muscat in Oman officially opened for business with a gala performance led by Placido Domingo (in front of the scenes) and a lot of guidance from the Kennedy Center (behind the scenes). The opera house announced its new season yesterday, and it turns out a lot of familiar faces, including the National Symphony Orchestra and the Farrell Ballet, will be appearing there in 2012-13.

The NSO played a sold-out concert at the storied Teatro Colon in Buenos Aires on Thursday; Friday night found them in Montevideo, Uruguay; and this weekend they moved on to Brazil for the tour’s final concerts.

On Monday at the Teatro El Circulo in Rosario, Argentina, the NSO played an unusual program: rather than mixing it up with a concerto or a shorter piece, they offered two symphonies — the Beethoven 7th and the Tchaikovsky 5th — back to back. “That will be a true test of our stamina,” said Marissa Regni, the orchestra’s principal second violinist, before the tour.

After talking to Hilary Hahn for my story on classical musicians and improvisation in last Sunday’s paper, I was excited to attend her performance at the Birchmere with Hauschka, her partner on the new CD ”Silfra,” on Monday night. Unfortunately, I was disappointed with the performance, as I wrote in my review.

The critics in Mexico and Trinidad were generally excited by the NSO’s appearance. Even at Bellas Artes in Mexico City, orchestras the size of the NSO don’t come through every day, so last week’s concert was a big event.

Washington’s music scene seems to me to have changed even since I got here in 2008; now, there’s still plenty going on through the month of June. The National Orchestral Institute and the Washington Early Music Festival, of course, predated my arrival by some years; both are going strong this month. Last weekend, Robert Battey thoughtfully reviewed the return of Leonard Slatkin to Washington at the helm of the NOI orchestra; and I checked out a WEMF concert by the ensemble The Wayward Sisters, a young quartet that won the 2011 Early Music Foundation/Naxos recording award (not to be confused with the London-based vocal trio of the same name). Joan Reinthaler, meanwhile, praised the women in the cast of Carmen presented by the Bel Cantanti Opera and Catholic University, but thought the men showed few signs of life, much less passion.

It used to be a central part of Western classical music; today, audiences are more likely to associate it with jazz, world music, or, if a classical musician is dabbling in it, crossover. The “it” in question is improvisation, which is, despite years of neglect, making something of a comeback in classical music. In this Sunday’s Washington Post, I take a look at some of the different ways classical artists approach improvisation.