The Complete Idiot''s Guide to Music Theory

Part 4:
Accompanying
178
When you transpose a note or a melody or a chord, you take it from one key,
and instead play the equivalent note, melody, or chord in another key.
For example, let’s say you’re playing the note C in the key of C—the key’s tonic
note. When you transpose that note to the key of F, you now play an F—which
is the tonic note for the key of F.
Sounds easy enough, doesn’t it?
Let’s look at a more complex example: Let’s say you’re in the key of C and you
play a melody that moves from C to D to E—the first three notes of the C
Major scale. When you transpose that melody to the key of F, the new notes
(the first three notes of the F Major scale) are F, G, A.
Getting the hang of it yet?
Here’s another example: Let’s say you’re in the key of C, and you’re playing the
I-vi-IV-V chord progression—C-Am-F-G. When you transpose that chord pro-
gression into the key of F, the new chords are F-Dm-B
-C. It’s still I-vi-IV-V;
just in a different key.
You can transpose from any one key to any other key. That means you could
move the notes anywhere from a half step to a major seventh up or down from
where you started. (You also can move notes up or down by whole octaves—
what is called 
octave transposition
—but you’re really not altering any notes;
you’re just changing octaves.)
Why You Need to Transpose
As you saw in the introduction to this chapter, there are many different reasons
you might need to transpose a song. Here are some of the most common:
◆
The song, as written, is out of the range of a vocalist or instrumentalist. If
a singer can’t hit the high notes in the key of C, maybe the key of B or B
,
or even A might be friendlier.
◆
You or another musician don’t know how to play the song in the given
key. This is especially a problem with beginning guitarists who don’t
always know the chords in some of the more extreme flat or sharp keys—
but they do know the chords for G and A and C and F. If you can trans-
pose the song to one of these keys, everyone can play their parts. (You
have the same problem with any instrument that has to deal with a lot of
sharps and flats in the key signature; it’s easier to play in C, G, D, F, and
B
than it is to play in the other, more complex, keys.)
◆
You’re writing or arranging for one of the many instruments that don’t
play in what we call 
concert key.
For example, trumpets always sound one
whole note lower than what is written—so you have to transpose all trum-
pet players’ music up a step so they’ll be in the same key as the other
musicians. (So if the concert key is C, you write the trumpet part in D;
when a trumpet plays a D, it actually sounds as concert C.) These instru-
ments are called 
transposing instruments
, because you have to transpose
their parts for them.
Concert key 
or
concert pitch
is the under-
lying key of a piece of
music—that is, the actual
pitches that sound when
played. The piano is
always in concert key.