Front door of original MEV studio, Rome.

Amid the firecracker-sized pops of an ancient LP, a fatherly voice corrects the iconic beginning of Beethoven's Symphony No. 5. "Sometimes it's played pum, pum, pum, pum," says (long-dead) legendary conductor Bruno Walter. "But zet's absolutely wrong! It's pah-pah-pah-pah!" So begins my favorite specimen of the most obscure genre in classical music: the conductor's bonus disc.

Once or twice a decade, record companies burnish a new release with an extra disc of a star conductor rehearsing, answering interview questions, or otherwise holding forth. Yet unless you want the proper pronunciation of "Beethovenian" from John Eliot Gardiner (say "bay-toe-VEE-nee-in") or yearn to eavesdrop on Sergiu Celibidache grunting his way through Bruckner, most bonus discs remain curios, of interest only to aspiring conductors and composers.

By contrast, the bonus CD accompanying Benjamin Zander's splendid recording Bruckner: Symphony No. 5 (Telarc) is a winner. Charming and earnest, Zander calls the massive piece of music "a vast and serious journey" and explains how to hear it as "a cathedral in sound." The album's additional mini-poster helps you follow Zander's hypothesis and defangs terms such as "recapitulation" and "scherzo." Renowned for his sumptuous Mahler recordings, Zander is an engaging guide who fulfills the mission of the bonus disc: to help you listen in a new way.

Norwegian sound artist Jana Winderen wants you to hear anew as well; equipped with submersible microphones—hydrophones—Winderen reveals the sonic beauty of the ocean. Her innocuously named EP Heated: Live in Japan (Touch) documents her improvising with a trove of recordings made in the icy waters of Greenland, Iceland, and Norway. I'm not surprised to learn that Winderen contributed hydrophone recordings to the Sigur Ròs film Heima; she shares the band's penchant for conjuring brooding, majestic desolation.

I'm also captivated by Crosstalk (Bridge), a compilation of what Harry Partch called "speech-music"—a nexus of ordinary speech, recitation, and songlike inflection heard everywhere from Schoenberg's 1912 masterpiece Pierrot Lunaire to verbally dazzling hiphop tracks. Here, processed electronics, raps, rants, and granular synthesis collide with voice-based works by Pamela Z, Shelley Hirsch, DJ Spooky, Vijay Iyer, and others. I'm particularly taken with tracks by George Lewis, DBR's mournful "Blimp/Sky," and Pamela Z's "Declaratives in the First Person."

Finally, don't miss MEV 40 (New World), a four-disc retrospective of the blazing, radical, and visionary live-electronics ensemble Musica Elettronica Viva. Italian for "live electronic music," MEV were founded in Rome during the damn-it-all efflorescence of the 1960s; since then, the group's core of Richard Teitelbaum, Alvin Curran, and Frederic Rzewski continue to transform the notion of live electronic music into a rowdy, passionate Happening. This is essential listening for anyone who loves electronic music. recommended