Expression is achieved through the manipulation of pitch (such as inflection, vibrato, slides etc.), volume (dynamics, accent, tremolo etc.), duration (tempo fluctuations, rhythmic changes, changing note duration such as with legato and staccato, etc.), timbre (e.g. changing vocal timbre from a light to a resonant voice) and sometimes even texture (e.g. doubling the bass note for a richer effect in a piano piece). Expression therefore can be seen as a manipulation of all elements in order to convey "an indication of mood, spirit, character etc." and as such cannot be included as a unique perceptual element of music, although it can be considered an important rudimentary element of music.