in which the pitch of a note varies in a pulsating rhythm. Mechanically, it is achieved by fingertip movements which alter the length of the vibrating string. There are several different styles of vibrato ranging from the use of just the fingers, to the use of the wrist or even the whole forearm. By employing these different techniques both the speed and amplitude of vibrato oscillations can be varied for musical effect. Vibrato is often perceived to create a more emotional sound, and it is employed heavily in music of the Romantic era. The acoustic effect of vibrato has largely to do with adding interest and warmth to the sound, in the form of a shimmer created by the variations in projection of strongest sound. A well-made violin virtually points its sound pattern in different directions depending on slight variations in pitch. Violinists oscillate backwards, or lower in pitch from the actual note when using vibrato, since aural perception favors the highest pitch in a varying sound. Vibrato does little if anything to disguise an out-of-tune note. Violin students, especially of beginner level, are taught to use it only on extended notes and or during points of emotional tension. Vibrato can be difficult to learn and may take a student several months, if not years, to master. Harmonics Lightly touching the string with a fingertip at a harmonic node while bowing close to the bridge can create harmonics. Instead of the normal solid tone a wispy-sounding overtone note of a higher pitch is heard. Each node is at an integer division of the string, for example exactly halfway along the length of the string, or exactly one-third along the length of the string. The pitch produced in these two cases will be an octave higher in the case of halves, and an octave and a fifth higher in the case of the string vibrating in thirds. A responsive instrument will provide numerous possible harmonic nodes along the length of the string. Harmonics are marked in music with a little circle above the note that determines the pitch of the harmonic. There are two types of harmonics: natural and artificial (also known as "false harmonics"). Artificial harmonics are more advanced than natural harmonics described above. Stopping a note on one string, for example first finger "E" on the D string, and having another finger just touching the string a fourth higher,