trans·pose 
/v. trænsˈpoʊz; n. ˈtrænspoʊz/ Pronunciation Key - Show Spelled Pronunci[v. trans-pohz; n. trans-pohz]
In a musical context, it means “ to reproduce in a different key, by raising or lowering in pitch” (Dictionary.com http://dictionary.reference.com/ In other words, you see a melody in one key, and play it in another. Why is it so important to know how to transpose?
Have you ever played in a musical and had to share the part because you didn’t know how to transpose it? Or how about this - have you had to give up a coveted part in orchestra to someone who had the specified instrument? Being able to transpose on sight can help you to keep that spot, or to play that fun lick in ‘Mambo’ from “West Side Story”. (This is not ALWAYS the case; there are times when – sigh – a saxophone really does make the piece sound better.)
Transposing by sight takes lots of practice but it is achievable.
Use this chart to get you started:
If you’ve never transposed anything, start with a basic major scale. Let’s say you’ve got a Bb clarinet and you have a "C" scale in front of you, but it's written for C Flute.
Using the chart, figure out what a concert "C" is on a Bb clarinet. (The answer is “D”.)
You will play a "D" scale.
Now, using the chart as your roadmap, continue to practice transposing scales. Don’t just learn to play the scales; you should be doing that already. TRANSPOSE them. Read a scale as written, then play it as if it’s a Flute part, then an alto sax part, etc. etc. The more you do it, the more automatic it becomes.
Next, write out a simple melody, one that you know (say, "Twinkle Twinkle Little Star") and go on from there! It’s a great skill to have and will serve you well in many ways.
Some things to watch for:
- Watch out for accidentals and key signatures!
- If you are transposing from a higher pitched instrument to a lower pitched (such as flute to clarinet for example) you may need to play an octave lower.
And, of course, have fun!
The clarinet clairvoyant