rt would probably be
written in the key of F, _i.e._, it would be transposed a whole step
upward; but, of course, the actual tones would be in the key of
E-flat. The player, in this case, would perform upon a B-flat
clarinet--_i.e._, a clarinet sounding pitches a whole step lower than
indicated by the notes. (It is called a B-flat clarinet because its
fundamental gives us the pitch B-flat--this pitch being a whole-step
lower than C; and it is because the pitch sounded is a whole step
_lower_ that the music has to be transposed a whole step _higher_ in
order to bring it into the correct key when played.) In the case of
the clarinet in A, the pitches produced by the instrument are actually
a minor third lower than the notes indicate (A is a minor third lower
than C, just as B-flat is a whole-step lower). In writing music for
clarinet in A, therefore, the music will need to be transposed upward
a minor third in order that when played it may be in the right key;
just as in the case of the clarinet in B-flat, it has to be transposed
upward a whole-step.

"Clarinet or cornet in B-flat" means, therefore, an instrument that
sounds pitches a whole-step lower than written; "clarinet or cornet in
A" means one that sounds pitches a minor third lower than written;
"horn in F" means an instrument sounding pitches a perfect fifth lower
than written (because F is a perfect fifth below C); while the
"clarinet in E-flat" sounds pitches a minor third higher than written.
Whether the pitches sounded are higher or lower than the notes
indicate will have to be learned by experience or study.

If the passage marked Fig. 1 were to be orchestrated so as to give
the highest voice to the clarinet and the lowest to the horn, the
clarinet and horn parts would appear as shown in Fig. 2.

[Music: Fig. 1]

[Music: Fig. 2

Clarinet in B-[flat]

Horns in F]

In order to make this information more specific, we add a table
showing the keys of the original and transposed parts. The practical
band man expresses the substance of this table tersely by saying,
"subtract 3 sharps or 2 flats."

ORIGINAL KEY TRANSPOSED KEY KIND OF INSTRUMENT
C D B-flat
G B-flat A
D F A
A C A
E G A
B D A
F-sharp A A
C-sharp E A
F