Wikipedia: Air on the G String
Air on the G String is August Wilhelmj's arrangement of the second movement in Johann Sebastian Bach's Orchestral Suite No. 3 in D major, BWV 1068.
The original orchestral suite was written by Bach for his patron Prince Leopold of Anhalt some time between the years 1717 and 1723.
The title comes from violinist August Wilhelmj's late 19th century arrangement of the piece for violin and piano. By transposing the key of the piece from its original D major to C major and transposing the melody down an octave, Wilhelm was able to play the piece on only one string of his violin, the G string.
Later, a spurious story was put about that the melody was always intended to be played on the G string alone.
The Air on the G String was the first work by Bach ever to be recorded. This was by the Russian cellist Aleksandr Verzhbilovich and an unknown pianist, in 1902 (as the Air from the Overture No. 3 in D major, BWV 1068).
Part of Air on the G String's melody was incorporated into Procol Harum's celebrated 1967 Worldwide hit, A Whiter Shade of Pale.
From Revision: J S Bach: Orchestral Suite in no.3 in d major, bwv 1068
The suite as a whole is perhaps most famous today for its second movement, the Air. In the 19th-century arrangement by August Wilhelmj in C major, it is widely known as the 'Air on the G-string' as the melody line can be played wholly on the lowest string of the violin, the G-string. This is often played in a highly Romantic style, with much vibrato. There have been other versions; French jazz pianist Jacques Loussier’s version was used in a cigar advert.
Its lyrical melody acts as Baroque version of a wordless, instrumental aria, which unfolds slowly, almost infinitely so. The air’s long opening semibreve, as a rhythmic device, can give the impression of eternity. But it is the walking bass that provides the forward momentum; the C# and A in bar 1 act as passing notes in the bass. The incessant quaver movement acts to unify the piece as well as to provide momentum, giving great balance of mood throughout the piece. The texture is not nearly as dense as the preceding overture, but it retains much of its polyphonic texture; the second violin and viola both have melodic fragments that answer the phrases in the main melody, creating an effect of antiphony.
The melodic construction makes great use of suspensions, which provide moments of harmonic tension within the air. The first one comes as bar 1 gives way to bar 2; the F# becomes dissonant with the changed harmony in bar 21, but is resolved by bar 23. However, in the intervening beat the melody is decorated by semiquavers on B, G, and an appoggiatura on F# just before the resolution of this 7-6 suspension to the E. There are many such highly decorated suspensions in the music – the viola has ones in bars 3 and 4; the second violin in bars 5 and 6. The decoration also extends into ornamentation, some of which Bach has written out and prescribed, but much of which can be added by the players in line with Baroque performance practice.
The air is structured within a binary movement framework:
section A: bars 1-6
section B: bars 7-18
But its tonal plan allows it to maintain great interest:
bar 1 - D major
bar 2 - A major (hinted at via dominant; the E major chord acts more like the tonic’s secondary dominant, as the bass G# is quickly cancelled by G in bar 2)
bar 3 - E minor
bar 4 - D major (the chord of E minor acts a pivot chord to return to the tonic)
bar 5 - A major (establishing the binary form; the G before the repeat changes the A major to an A dominant 7th to lead back to the D major)
bar 7 - E minor
bar 9 - B minor (establishing the relative minor)
bar 11 - A major
bar 13 - G major (via the A dominant 7th chord acting as secondary dominant; starts sequence)
bar 13 - A major (sequence continues, increasing tension)
bar 14 - B minor (sequence continues, further tension)
bar 14 - E minor (final stop of the sequence)
bar 15 - G major (a typical move of Bach to refer to the subdominant before returning via the dominant chord to…)
bar 17 - D major
The melodic sequence of bars 13-14 serves as a modulating sequence, and increases tension via its chromaticism, progressing from the dominant in first inversion to the tonic in each key. It also marks some contrast, as the sequence is ascending, whilst much of the rest of the piece uses descending melodies and bass lines. Again, the walking bass shares these features with the texture as a whole, acting as a microcosm; however, its constant quaver movement provides some continuity, despite the rate of harmonic change increasing from a steady 2-chords-per-bar to a 4-chords-per-bar in the sequence.