Become a more discerning classical-music listener — and never accidentally buy the synthesizer interpretation of the Goldberg Variations again. The New York Times Essential Library: Classical Music: A Critic's Guide to the 100 Most Important Recordings (Henry Holt, $12, www.amazon.com), by music critic Allan Kozinn, is a collection of short essays that trace 900 years of the most influential classical music — from Gregorian chants to Philip Glass. The book is also a buying guide to help you avoid confusion the next time you're lost somewhere between "Beethoven" and "Wagner."