stylistic:style_transfer
c. 1760–1830

While the bassoon was still often used to give clarity to the bassline due to its sonorous low register, the capabilities of wind instruments grew as technology advanced during the Classical era. This allowed the instrument to play in more keys than the dulcian. Joseph Haydn took advantage of this in his Symphony No. 45 ("Farewell Symphony "), in which the bassoon plays in F-sharp minor. Following with these advances, composers also began to exploit the bassoon for its unique color, flexibility, and virtuosic ability, rather than for its perfunctory ability to double the bass line. Those who did this include Ludwig van Beethoven in his three Duos for Clarinet and Bassoon (WoO 27) for clarinet and bassoon and Niccolo Paganini in his duets for violin and bassoon. In his Bassoon Concerto in B-flat major, K. 191, W. A. Mozart utilized all aspects of the bassoon's expressiveness with its contrasts in register, staccato playing, and expressive sound, and was especially noted for its singing quality in the second movement. This concerto is often considered one of the most important works in all of the bassoon's repertoire, even today.

The bassoon's similarity to the human voice, in addition to its newfound virtuosic ability, was another quality many composers took advantage of during the classical era. After 1730, the German bassoon's range expended up to B♭, and much higher with the French instrument. Technological advances also caused the bassoon's tenor register sound to become more resonant, and playing in this register grew in popularity, especially in the Austro-Germanic musical world. Pedagogues such as Josef Frohlich instructed students to practice scales, thirds, and fourths as vocal students would. In 1829, he wrote that the bassoon was capable of expressing "the worthy, the virile, the solemn, the great, the sublime, composure, mildness, intimacy, emotion, longing, heartfulness, reverence, and soulful ardour." In G.F. Brandt's performance of Carl Maria von Weber 's Concerto for Bassoon in F Major, Op. 75 (J. 127) it was also likened to the human voice. In France, Pierre Cugnier described the bassoon's role as encompassing not only the bass part, but also to accompany the voice and harp, play in pairs with clarinets and horns in Harmonie, and to play in "nearly all types of music," including concerti, which were much more common than the sonatas of the previous era. Both Cugnier and Étienne Ozi emphasized the importance of the bassoon's similarity to the singing voice.

The role of the bassoon in the orchestra varied depending on the country. In the Viennese orchestra the instrument offered a three-dimensional sound to the ensemble by doubling other instruments such as violins, as heard in Mozart's overture to The Marriage of Figaro, K 492. where it plays a rather technical part alongside the strings. He also wrote for the bassoon to change its timbre depending on which instrument it was paired with; warmer with clarinets, hollow with flutes, and dark and dignified with violins. In Germany and Scandinavian countries, orchestras typically featured only two bassoons. But in France, orchestras increased the number to four in the latter half of the nineteenth century. In England, the bassoonist's role varied depending on the ensemble. Johann Christian Bach wrote two concertos for solo bassoon, and it also appeared in more supportive roles such as accompanying church choirs after the Puritan revolution destroyed most church organs. In the American colonies, the bassoon was typically seen in a chamber setting. After the Revolutionary War, bassoonists were found in wind bands that gave public performances. By 1800, there was at least one bassoon in the United States Marine Band. In South America, the bassoon also appeared in small orchestras, bands, and military musique (similar to Harmonie ensembles).