It's never too late to learn how to read music. Liz Fleischer, who teaches at Lucy Moses among other institutions, is probably the one to teach you. She is arguably NYC's best sight-singing coach, and has perfected a method that has worked for hundreds of singers, including this reviewer.
She teaches in a group-setting, dividing her classes into skill levels. If you miss her selecting period, you can drop into almost any class and try to join in. After the class, she will be able to tell you exactly which level is right for you. Her classes (which require hardly any homework at all) teach rhythm, relative and absolute pitch, key signatures and tone, with a bit of theory thrown in for better comprehension.
One of Liz's most amazing gifts: in a room full of people trying to sing timidly enough not to have their mistakes overheard, she can hear YOU perfectly - as well as all of your neighbors in the class. It is a Santa Claus-like talent - how can she pay attention to everyone as if they were the only one in the room? Does she have 17 ears?
Liz comes highly recommended by choral conductors and instructors - notably Lyndon Woodside, 30-year veteran conductor of the venerable old Oratorio Society New York. If you are planning to try out for this choir, the NY Choral Society, or similar choirs and you feel at all shaky on your sight-singing skills, sign up for a refresher with Liz. All of these choirs include a sight-singing test at their auditions.
Here is an article that Liz wrote: http://www.classicalsinger.com/magazine/article.php?id=779
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