I need to change the key of a song I’m playing. The song is changes by David Bowie and I’m hoping to change it from the original key in piano (C) to my baritone saxophone (the bari sax is in the key of Eb but I’d play it in the key of A) I’m very confused and I don’t even know if I’m doing it right. Someone please help.
Basic transpositions for sax,l trumpet etc
Bb instruments (Bb clarinet, tenor/soprano sax, trumpet ...) Up one tone. C => D, F => G etc
Eb instruments (alto/baritone sax) Down 3 semitones. C => A, F => D etc
Players of transposing instruments need to know these by heart (and being able to do simple transposition more or less by sight is also recommended.)
Saxophone are transposing instruments:
Your instrument is called Eb-Sax because it plays an Eb when you play a written C. This means it transposes a minor 3rd up (and as a Bariton an 8ve down!)
So you have to notate and play an A on your instrument when you want to hear C. (your instrument will transpose the A a minor 3rd up ...)
It seems from your question that you want to play a song in C major on your baritone sax so you can play it in the same key as any accompanying instruments (that is, in "concert pitch"). To do that, you have correctly identified that you will be playing in the key of A major.
You can do this at sight by imagining that the treble staff's bottom line isn't there, and that it has an extra line on the top. In other words, the real G line that has the treble clef on it becomes an imaginary E line. You also need to add the key signature for A major to your imagination, which comprises three sharps, namely, F#, C#, and G#. Any accidentals on those notes will have to be adjusted accordingly, so for example if there's an Eb in the original, the transposed note is a C-natural.
This will be easier for some people than for others. This technique may also be more difficult if it transpires that you need to transpose up a major sixth instead of down a minor third.
Another way of doing it is just to think relatively. That's how I have done it in the past when playing Bb trumpet from a concert-pitch score. That is, when you see a written D, for example, you know it's the second degree of the C-major scale, and since you're playing in A-major, you play the second degree of the A-major scale, which is B.
In older times, musicians learned to read every possible C clef in addition to the treble and bass clefs, so the technique for transposition would be to imagine that the notes were written in a different clef. For this transposition, you would imagine that the C clef is on the bottom line. If you ever have to play a cello part on baritone sax, or any other part notated in bass clef, just imagine that it is notated in treble clef.
The end result is that the distances between the notes of the melody remain the same when measured in half steps.
If you have difficulty doing this at sight, write it out. I encourage you to do it by hand rather than using a computer, because you will learn the music better that way. Start with a treble clef and the correct key signature. Copy each note that's on a line to the next lower line, and copy each note on a space to the next lower space.
Finally, if even that proves difficult for you, you can copy the music verbatim into a computer music notation program and then use the "transpose" function to lower the pitch by a minor third or raise it by a major sixth. Again, I encourage you to copy the end result by hand to gain experience in writing music by hand and because hand copying (in my experience, at least) leads to a more thorough understanding of the music than does entering it into a computer.
Here's the quick dodge for transpositions (as long as you know your key signatures!) E♭ baritone has three 'built-in' flats. It's 'in E♭' after all! So, to play music for an instrument 'in C' (i.e. normal untransposed piano, no 'built-in' flats or sharps) we have to take away those three flats. Which is the same as adding three sharps.
So yes, to match C on piano, your bari will need to play in A. To match F (one flat) it would need to play in D (two sharps). Get the idea?