Although a particular key signature appears at the start, it is common to move to other keys during a piece of music. This is called modulation. The most common modulations are between relative major and minor, and between keys which are close together in the key cycle, but it is possible to move freely from any key to any other key as long as it sounds good. The following Ballad in the key of Bb major modulates to several other keys before returning to Bb major at the end. Notice the use of W time here.