Shostakovich: Trio in E minor, third movement

One of the things that Shostakovich is famous for is his use of the passacaglia form. As Wikipedia tells us this originated in 17th century Spain (on the guitar as a matter of fact) as a simple chord progression used to accompany, as the name tells us, a procession down the street. It soon became a favorite of Baroque composers in the form of a set of variations over a repeated bass line or chord progression.

There are a number of famous passacaglias by Shostakovich, who tended to use it to create powerful laments. This one is an expressive duet for the violin and cello over a set of chords in the piano that repeat six times. Here is that progression:

This progression outlines two tetrachords (groups of four notes). The first is in the tonic key of B flat minor and has the notes B flat, F, G natural and A natural. The A natural would normally lead us back to the tonic B flat, but Shostakovich follows it with a second tetrachord F#, G natural, A natural, B natural which suggests a modal E minor, the key of the first movement and the work as a whole.

Incidentally, the B natural that the progression ends on is in a Neapolitan relationship with the tonic: a semitone higher (which we would easily see if it were spelled C flat). Where else have we seen a Neapolitan relationship? Oh yes, in the second movement scherzo where the contrasting middle section was in G major, a Neapolitan relation to the tonic F# major. A very famous use of this kind of relationship is in the transition from the first to the second movement of Beethoven's late C# minor quartet. The first movement is in C# minor and the second in D major, the Neapolitan.

Here is the melody as it first appears in the violin. It is quite a long one, 45 seconds long, so requires three lines:

Some features: it begins with an upbeat fifth to tonic leap, just as the scherzo did. From there it mostly moves by step and features a mournful turn figure that comes three times. The movement unfolds with variations on this melody in both violin and cello and ends with a B natural pedal and outlining the chord of E minor.

Let's listen to that performance by Argerich, Kremer and Maisky: