D4. Cooper, L. Hugh. The Double Reed 1/3 (December 1978): 31.

For pianissimo slur from D3 to D4.

D3:                   D4:
       Db                    Db
 x  x  o | o o o       x  x  o | o o o
            E
Bb B C D              Bb B C D

D4. Corey, Gerald E. "How to Improve Your Tuning on the Bassoon." The Journal of the International Double Reed Society 8 (1980): 32.

European fingering:
x x o | x x o F

In order to raise the pitch, Corey prefers:
x x o | o o o
       Bb

In extreme cases:
x x o | o o o
         E

D4. Groeling, Charles R. "Cultivating Bassoonists." The Instrumentalist 47/1 (August 1992): 50. Swanson, Robert. "Pictorial Bassoon Fingerings." Woodwind Magazine 4/1 (September 1951): 9. Turkovic, Milan. In Klimko, Ronald. Bassoon Performance Practices and Teaching in the United States and Canada. Idaho: University of Idaho, 1974, p. 70. Cooper p. 182 (no whisper key).

x x o | o x x F

D4. Spittel, Richard. In Apfelstadt, Marc and Klimko, Ronald. Bassoon Performance Practice, Teaching Materials, Techniques and Methods. Idaho: University of Idaho, 1993, p. 57.

x x o | o o o
       Bb

Heckel-system bassoon fingerings by note name