Productions of the Metropolitan Opera are broadcast live in 1,700 movie theaters in 54 countries. A broadcast of Renee Fleming in "Thais." Mike Mergen for The New York Times

When you walk to your seat in a movie theater for one of the "Live in HD" broadcasts of the Metropolitan Opera in New York, your experience begins with the sound: the instantly recognizable, immediately comforting hum of instruments tuning and the audience stirring, piped in live from the Met itself.

As the Met says on its Web site, "It is the next best audio experience to being in the opera house itself."

The question is whether "the next best" is good enough when it comes to the complete opera experience. The Met is leading a revolution, albeit one that has less to do with what it's putting onstage than with how it's sending it into the world.

None of which is to diminish the significance of the series. Fundamentally changing the way the performing arts can be delivered to audiences, the broadcasts are the most important thing to happen in opera since the advent of translated super titles in the early 1980s. The "Live in HD" series, which began six years ago, now reaches 1,700 theaters in 54 countries.

But how does the movie theater experience compare with the live - really live, not live in HD - production in the house?

To find out I attended the Met's 11 HD broadcasts around America. While the sound quality in the theaters is exceptional, the microphones can't capture differences in the size of voices. But the visuals are often thrown into higher relief. In getting so close to the performers the broadcasts can create remarkably strong moments.

Some singers can effectively bridge the formats; others - like Renee Fleming, who sang the title character in "Rodelinda" - may cut an elegant, affecting figure onstage but are less convincing when their eyes need to carry the drama.

For still others the new medium is a godsend. When I saw Natalie Dessay at the Met in "Lucia di Lammermoor" in February 2011, her radically introverted conception of the role seemed simply dull and detached; later in HD it was haunting.

If all 17 performances of this season's new production of "Don Giovanni" had sold out the 4,000-seat Met, it would have accounted for a total audience of 68,000. The broadcast of the opera in October, by contrast, reached 216,000 worldwide at one time, and the Met expected 50,000 more to see it in delayed showings in Asia, Australia, New Zealand and South Africa, and in "encore" broadcasts in North America and Europe.

The number of broadcasts now encompasses about a third of the Met's Saturday matinee performances; the number is limited by the series's cost and logistical challenges, as well as by the company's reluctance to repeat operas year to year.

With tickets costing about $20, the program has begun turning a profit for the Met.

The program speaks to the vision of Peter Gelb, the Met's general manager, as a promoter. The rest of the arts world was unprepared for the program's success. Other opera companies have only haltingly begun to explore the approach, with theater companies (like the National Theater in London), dance troupes (the Bolshoi Ballet in Moscow) and symphony orchestras (the Los Angeles Philharmonic) following suit.

In certain of the Met's new productions this season - "Don Giovanni," Gounod's "Faust," Wagner's "Ring" operas - the action often seems limited in front of looming empty backgrounds waiting to be found by the cameras. The party scene in "Don Giovanni" was diffuse at the Met; in the movie theater it was clear what to look at. Your attention felt, finally, directed.

The Met denies that artistic decisions are made with an eye toward the broadcasts. "The most unjustified criticism (coming primarily from music critics such as yourself)," Mr. Gelb wrote to me recently, "is that the singers, directors and designers are creating stage productions at the Met that are planned with HD in mind."

The New York Times