Clavichords were built as far back as the early fifteenth century, and perhaps earlier. This most personal, simplest, and quietest of European keyboard instruments was the perfect vehicle for music pedagogy, keyboard practice, and composition throughout its 400-year history. The action of the clavichord is relatively simple: the finger depresses a key which, working as a lever, causes its opposite end to rise so that a metal tongue (or tangent) hits a metal string, causing it to resonate. When the key is released, the string is damped. The clavichord is very quiet compared to the harpsichord or piano because of the inefficiency of its sound production, with the tangent hitting the string at the end of its resonating length, rather than in the middle. The tangent mechanism, however, allows a player to achieve a range, albeit narrow, of louder and softer tones as well as special effects like bebung, a form of vibrato, so that the clavichord was and is valued for its intimate expressiveness. Earlier clavichords were fretted, that is, a single string might be used to create several different notes, depending on where a tangent struck it. Unfretted clavichords, with a single note per string, came into use in the late seventeenth century.