For pre-digital natives, there's nothing quite as nostalgia-inducing as the manual "click," "clack" and "ding" sounds of an old mechanical typewriter. That's why The Boston Typewriter Orchestra is making these old machines quite literally "sing" again. Since 2004, this six-man ensemble has been playing a range of covers and original songs on both desktop and portable machines from years past. And if you thought all typewriters emitted the same sounds, think again. This orchestra's sonorous symphonies have captivated crowds all over New England.