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Your choice of new key will depend on why you are transposing, but it may depend on other things, also.
- If you are transposing because the music is too low or too high, decide how much higher or lower you want the music to sound. If you want the music to sound higher, go around the chromatic circle (Figure 6.25) in the clockwise direction. If you want it lower, go in the counterclockwise direction. The further you go, the more it will change. Notice that, since you're going in a circle, raising the music a lot eventually gives the same chords as lowering it a little (and vice-versa). If some keys are easier for you to play in than others, you may want to check to make sure the key you choose has "nice" chords. If not, try another key near it.
- If you are changing keys in order to make the chords easy to play, try changing the final chord so that it names an easy-to-play-in key. (Guitarists, for example, often find the keys G, D, A, E, C, Am, Em, and Dm easier to play in than other keys.) The last chord of most pieces will usually be the chord that names the key. If that doesn't seem to work for your piece, try a transposition that makes the most common chord an easy chord. Start changing the other chords by the same amount, and in the same direction, and see if you are getting mostly easyto- play chords. While deciding on a new key, though, keep in mind that you are also making the piece higher or lower, and choose keys accordingly. A guitarist who wants to change chords without changing the pitch should lower the key (go counterclockwise on the circle) by as short a distance as possible to find a playable key. Then capo at the fret that marks the number of keys moved. For example, if you moved counterclockwise by three keys, put the capo at the third fret.
- If you are changing keys to play with another instrumentalist who is transposing or who is playing in a different key from you, you will need to figure out the correct transposition. For a transposing instrument, look up the correct transposition (the person playing the instrument may be able to tell you), and move all of your chords up or down by the correct number of half steps. (For example, someone playing a B flat trumpet will read parts one step - two half steps - lower than concert pitch. So to play from the same part as the trumpet player, move all the chords counterclockwise two places.) If the instrumental part is simply written in a different key, find out what key it is in (the person playing it should be able to tell you, based on the key signature) and what key you are playing in (you may have to make a guess based on the final chord of the piece or the most common chord). Use the chromatic circle to find the direction and number of half steps to get from your key to the other key.