can impede the independence of the lines. For example, in m. 38 of the gigue from his English Suite No. 1 in A major, BWV 806, J.S. Bach avoids excessive parallel harmony in order to maintain the independence of the lines: parallel thirds (at the beginning) and parallel sixths (at the end) are not maintained throughout the entire measure, and no interval is in parallel for more than four consecutive notes. Consideration of doubling is important when following voice leading rules and guidelines, for example when resolving to an augmented sixth chord never double either notes of the augmented sixth, while in resolving an Italian sixth it is preferable to double the tonic (third of the chord). Some pitch material may be described as autonomous doubling in which the part being doubled is not followed for more than a few measures often resulting in disjunct motion in the part that is doubling, for example, the trombone part in Mozart's Don Giovanni. Doubling in orchestration In unison Instrumental doubling plays a crucial role in orchestration. Near the start of Schubert's Symphony No. 8 (the "Unfinished" Symphony), the oboe and clarinet play a theme together in unison, an "evocative and uncommon combination," "an embodiment of melancholy... over a nervous shimmer of semiquavers in the strings". At the octave The opening theme of the last movement of Mozart's Piano Concerto No. 24 is played throughout by the violins, but selected phrases are doubled, firstly by the flute playing an octave above; followed by the bassoon an octave below. Finally the violin is joined by both oboe and bassoon together, creating a doubling spanning three octaves: The opening bars of the third movement of Janáček's Sinfonietta combine unison and octave doublings. The passage illustrates how subtle and carefully differentiated doubling can contribute to the sound of a delicate and nuanced orchestral texture: In these three bars, the Bass Clarinet and the Tuba simultaneously sound a sustained pedal point on a low E flat, creating a distinctive blend of timbres. Similarly, the harp arpeggios are also doubled at the unison by the violas, while the first violins and ‘cellos double the main melody an octave apart. Drop voicings One nomenclature for describing certain classes of voicings is the "drop-n" terminology, such as drop-2 voicings, drop-4 voicings, etc. (sometimes spelled without hyphens). This system views voicings as built from the top down (probably from horn-section arranging