Organists learn how to mix the various stops, or ranks of pipes, to provide pleasing combinations of sound—at times a “thin” registration of a solo with simple accompaniment, and at other times the massive sounds of “full organ.” They are able to produce sounds that are not only pleasing, but which have become typical for certain periods and styles of music. They accomplish this, because they understand the different families of pipes, as well as the more subtle differences of ranks within each family.

A similar phenomenon exists in the world of orchestral instruments. Instrumental writers and directors know which instruments will sound best in a given situation. Because they know the distinctive sounds of each instrumental family, of each instrument within a given family, and even of the different segments of a particular instruments range, they also know how to substitute some instruments for others in situations that are not “standard.” We might call this phenomenon “instrumental registration.”

Composers and arrangers who write music that includes instruments may have preferences for certain instruments, depending on the composition and its use. Often publishers print parts for only those instruments, when others would also be effective—partially because it is economically difficult to anticipate and print for all the possibilities.

A problem arises at the point of use, when the indicated instruments are not available. However, there may be access to other instruments; and the music director, like the organist who can choose effective stops on an unfamiliar instrument, can learn how to substitute some instruments for others.

Among the three major melodic/harmonic families of instruments (woodwinds, brasses and strings), we might look at the woodwinds as a bridge between the other two—able to make some substitutions for either brass or stringed instruments. One of the more obvious areas is the substitution of woodwind instruments for stringed instruments, and vice versa. Flutes, oboes and clarinets can cover for violins; clarinets and alto saxophones can substitute for violas; and bassoons, bass clarinets and baritone saxophones can replace cellos. Due to their great range and blending quality, “regular” B-flat clarinets are very useful substitute instruments—even playing cello parts that aren't written in the cello's low range.

There are not as many effective substitutions between the woodwind and brass families. In Baroque literature, parts for two oboes are often interchangeable with parts for two trumpets. A trumpet, played with a straight mute, can play oboe and soprano or alto saxophone parts, if it is not played too loudly. A good trombone player can, to some extent, imitate a bassoon. If three trumpets are scored, but only two are available, a soprano or alto saxophone can blend in, particularly on the middle voice. A baritone saxophone can bark out trombone parts rather well.

Substitutions can be made within an instrumental family, also. Clarinets can play oboe and alto or tenor saxophone parts. French horns in their high range can cover 2nd trumpet parts, and in their low range can substitute for upper trombone lines. Baritones (euphoniums) and trombones can exchange parts.

Don't be afraid to make instrumental substitutions. Like an organist, the instrumental director can pull out all the stops!