Knowing the harmonic underpinning of a line can lead to a convincing interpretation. In the case of Shostakovich you might not think that's so important.
Just playing through the bassoon part to the 4th and 5th movement of the 9th Symphony, you barely notice a particular harmonic base. In fact, a lot of it sounds atonal.
However, a close look at the score reveals a very traditional harmony for both passages in the 4th movement.
In the passage above I've used a "c" to denote all bassoon pitches that fit in the F major chord. All dissonant notes are circled.
Knowing whether or not a particular note is dissonant or not opens avenues for interpretation. The "d" half note 11 notes in is quite dissonant and long in duration. It also makes up the first note of the half note motive outlined in my previous post.
Therefore, this should be a real point of tension in the line. I make a crescendo to the "d", give it a strong beginning and hold onto it a little longer than two beats.
Another obvious tension point is the high "Db" right after the quarter rest. To bring this out I elongate the quarter rest (this allows the F major harmony in the strings to shine through for a brief moment), stretch and increase tension on the "F" just before the "Db" and lengthen the "Db".
Since there is no meter, varying the length of the rests in this passage can add to the dramatic effect. I like to minimize the last quarter rest (before the final "Eb"-"C") in order to show that the tension is not really gone until the consonant C is sounded at the very end. I don't agree with the practice of some who like to breathe during this rest -- it lets up on the tension before it's time to do so. Don't breathe, but hold out the "Db" before the rest longer than normal length, rest and come right in with the "Eb".
The second passage follows suit. A major, first inversion. Look for the dissonances and consonances in this one. They are placed strategically throughout the line. I extend the final crescendo in order to stress the dissonance of the "Bb" towards the end.
The effect of playing this in the orchestra can be simulated by having three other bassoonists hold the chords while you play. You can really hear the harmonies this way! Trade parts and let everyone else have a turn with the solo.
Alternatively, have a pianist play the chords while you play the bassoon part. The pianist will need to re-strike the chords several times during the playing to keep the sound of the harmony alive.
I'd like to thank Doug Spaniol, Bassoon Professor at Butler University, who introduced me to the harmonies of this movement during a master class he gave for my students at Michigan State University many years ago.