Transposition

This is a preview of the educational program A Jazz Improvisation Almanac which is under development for the Outside Shore Music Online School. Feel free to browse this preview and learn what you can from it. For a more completed product, though, check out the original freely browsable jazz textbook, A Jazz Improvisation Primer.

All instruments used in Western music read music in the same way. That is, the note:

[EXAMPLE]

is called middle C, no matter what instrument one plays. However, middle C does not sound the same on all instruments. For example, the note C on a trumpet corresponds to the note Bb on a piano:

[EXAMPLE]

In order to play the note that corresponds with middle C on a piano, a trumpet player must play the D a step above middle C:

[EXAMPLE]

When music is written for trumpet, everything must be transposed a whole step up in order to be able to play with other instruments. For example, here is a phrase written for piano:

[EXAMPLE]

Here is that same phrase written for trumpet:

[EXAMPLE]

If a trumpet player is asked to read from music written for piano, he must do the transposition mentally. Most players of transposing instruments find themselves forced to do this from time to time.

Instruments that do not need to transpose, such as the piano, are referred to as C or concert key instruments. The trumpet is referred to as a Bb instrument, because the note C played on the trumpet corresponds to a Bb in concert key. Most wind instruments have to transpose in this fashion. The flute and trombone are among the few commonly used in jazz that do not. Besides the trumpet, other Bb instruments include the clarinet, soprano saxophone, and tenor saxophone. The tenor saxophone actually sounds an octave lower than the other Bb instruments mentioned.

The alto and baritone saxophones are Eb instruments. The note C notated for the alto saxophone corresponds to the Eb below this in concert key. The baritone saxophone sounds an octave lower than the alto. The phrase above written for alto saxophone looks like this:

[EXAMPLE]

The reason these instruments are built this way is mostly historical. You may wish to skip this explanation, as it is not necessary to understand this in order to learn anything about jazz. Some of you may find this interesting, however.

Most modern instruments are tuned and played such that all half steps are exactly the same size, and each whole step is exactly two half steps. However, the physics and mathematics of sound do not cooperate with this notion. Before the rise of the chromatic scale, music was based on simple integer ratios, developed by the Pythagoreans of ancient Greece. The ratio of the frequencies of C and G was originally defined to be 2:3, and the ratio of the frequencies of one C and the next C is defined to be 1:2. If one divides the octave into twelve equal intervals to form a chromatic scale, however, one will find that the note G from the chromatic scale does not correspond to the expected ratio:

[EXAMPLE]

The major scale and other scales used by the Pythagoreans were derived from these integer ratios. The result was that one could not arrange the resulting notes to form a chromatic scale in which all half steps are the same size.

Note that if an instrument is tuned or played such that its half steps are not all the same size, then the assumption that enharmonic spellings are interchangeable may not be valid. Some classical violin players, trained in Pythagorean tuning, will insist that F# and Gb are not really the same note, for example, since one comes from an integer ratio within the D major scale and the other from the Db major scale, and the frequencies do not exactly correspond.

Furthermore, instruments tuned to a particular scale would normally sound best only when playing in the key of that scale. For instance, here is an instrument tuned to the A major scale playing in A major:

[EXAMPLE]

Here is that same instrument playing in Bb:

[EXAMPLE]

To ears accustomed to the former, the latter was extremely dissonant. To allow music to be played in any key, different versions of each instrument would be created for different keys, and a musician would select the appropriate instrument for the key he was playing in. The same fingering pattern would then produce different pitches on the various different instruments of the family. For instance, the note produced by covering all finger holes on a Bb clarinet is D, but the same fingering on an A clarinet produces a C#:

[EXAMPLE]

Rather than require musicians to remember a different set of fingerings for each instrument in the family, it was easier to transpose the music. That way, a given note as notated would always be fingered the same way, regardless of the key of the instrument. Once a player learns one instrument in a family, he is able to play all instruments in that family.

Eventually, as more instruments were tuned chromatically and were therefore able to play well in any key, there was no longer a need for a different instrument for each key. Still, for many instruments, some keys would be easier to play in than others because of the fingering, so different versions of those instruments survived due to convenience.

Among trumpets, the Bb trumpet is by far the most common, but many orchestral players will also have a C trumpet. These instrument are close enough in size that the different in sound is negligible. In the case of the saxophone, however, the difference in size between the soprano, alto, tenor, and baritone is significant, and as a result they sound very different from each other, and this is an important part of why these different saxophones are still in wide use today.

Copyright 2000 Outside Shore Music
Authored by Marc Sabatella

Transposition