So just for fun, let's take one that is seldom moved to a different key because it's quite a study to learn it in the original key in the first place -- good old Body And Soul. Music by Johnny Green -- I hope his heirs have a hold on this copyright -- what a classic, well-crafted offering! Trane did not move the key on this one, but ya never can tell when a vocalist needs a little relief on the high notes, and I've discovered I get a better resonance on the lows and can easily make the high notes if it's a step lower. Heresy, blasphemy, I know -- Body And Soul in B natural -- please. Come on now, if it was Billie Holiday up here you'd move the key -- yeah, I know I'm not... -- but she sang in B sometime, just do me a favor, OK? I haven't tried the tenor sax in the lower key, yet, but landing on C# (either a thin, open fingering or all closed with the octave key) might be uncool. Anyway, let's consider navigating the change from Db to B natural -- which is one of the worst!
Below: Step 3, look at the Roman numerals, simplify even further into "home" or "away," highlight the cliches. Then, Step 4, we can easily move to the new key. Remember, too, that the 1st 8 is good for a total of 3 repetitions. And relax, see the simplicity of the bridge -- two different keys -- a cliche in the middle, and a surprise modulation in the very last measure.
Looking at Step 3, the simplified Roman numeral chart -- first 2 bars an easy to remember variation based on the ii chord, measures 3-4 an easy pattern based on I. Then bars 5-6 are a slight variation on a typical minor chord descending bass. The III7 on beats 3-4 of measure 6 can be considered part of the cadence, bars 7-8: | vim7 / iim7 V7 | I6 / x y || The bridge is pretty sensible. Up the scale in the new key (a half-step higher - we got there from bVI7) || I / ii / | iii / iv / | then back down with a 3-6-2-5-1 action, that's the first 4 of the bridge. Then the common device of changing the I chord to a Dorian minor changes the key a whole step lower, and bar 5 of the bridge is just a ii-V. Then bar 6 goes to iii (sub. for I) and down a half step on beats 3 and 4. | iim7 / V7 / | iii / biii(dim) / | Measure 7 of the bridge another ii-V (the key we're in now is a half-step below the original key) then the quite recognizable modulation in the last bar of the bridge, parallel dominant chords on beats 1, 2, 3. That set us up to go back to the ii chord of our original key. Smooth!