Review: Two ASO conductors celebrate a decade together, although Spano not a winning pianist

After a string of exceptionally gripping performances this season, it’s clear the Atlanta Symphony Orchestra has kicked itself up in quality.

Its range of expression often seems wider than in past years, with higher peaks and deeper emotions. The orchestra is playing with more finesse, intensity and humanity -- in a word, more “musically.”

Two of the reasons behind this advancement are being celebrated this week in Symphony Hall, with ASO music director Robert Spano and principal guest conductor Donald Runnicles collaborating in Mozart’s popular Piano Concerto No. 20. In large part, the concert celebrated two men coming into full midlife maturity as artists.

An occasional pianist -- at least in public -- Spano was at the keyboard Thursday night; Runnicles was on the podium.

As Spano charged from backstage to the piano bench, he looked nervous and announced to the audience that it was Mozart’s 255th birthday. “Sadly, he couldn’t join us!” he added, manically, to laughter.

But an air of levity, especially from Spano, meant that this dark-key concerto would likely not probe the depths for which it is admired; the evening’s pianist was lowering expectations.

Indeed, he played the notes but never seemed to lose himself in the music, and in fast sections he was just hanging on. But in the slow, lyrical “Romance” movement, he offered many pleasant insights -- emphasizing a harmonic pivot or illuminating the counterpoint. In addition to being a part-time pianist, Spano is a sometime composer, and he played his own cadenzas -- a brief, showy solo passage -- borrowing ideas from Mozart and Beethoven and sounding at once classical and harmonically modern.

Musically, the bigger event of the evening was Runnicles conducting Bruckner’s Symphony No. 8, a sort of Gothic cathedral in sound, built up of massive stone blocks. It was another peak experience from the Scottish conductor: searching, mystical and heartbreaking.

Over the 2010-11 season, the ASO has commissioned 10 composers to write short, introductory fanfares, representing Spano’s decade as music director. The latest, premiered Thursday, was Mark Grey’s “Ahsha,” which the California composer says was inspired by Spano’s fascination with ancient Persia. The title is derived from sacred Zoroastrian texts.

Although Grey is best known as the high-tech “sound designer” for distinguished American composer John Adams, his “Ahsha” was all-acoustic, with no electronics in the sonic mix.

The two-and-a-half-minute fanfare opens with low brass and horns in a majestic, perhaps exotic, setting. As the rest of the orchestra joins in, the mood darkens and starts to churn and the soundworld become prismatic, begging us to invent visual images. But his themes are not clearly characterized, the orchestration is sometimes hazy and the works rambles.

Still, a fanfare succeeds if it sets up a jubilant mood for what follows, and “Ahsha” had us ready to celebrate.