A student called me last week and mentioned that he was having problems playing some songs by ear. He mentioned two in particular–“Sleigh Ride” and “Winter Wonderland.”
I knew immediately what he was talking about, and he is correct. Those songs are more difficult to play by ear because of a shared common trait: they change keys within the song. The key signature does not change but the key itself clearly does.
Changing keys within the song and then returning to the original key is very common in that kind of music (Broadway style from the first part of the 20th Century). Many of the classic American Christmas songs do it.
Let’s take a look at “Winter Wonderland. The form is AABA.
Here are chords that would work for the A section if we are playing in Eb.
Eb Fm7 | Gm7 C7 | Fm7 | Bb7
Am7 D7 | Gm7 C7 | F7 Bb7 | Eb
And here is the B section:
G Am7 | Bm7 Am7 | G Am7 | Bm7
Bb Cm7 | Dm7 G7 | C7 F7 | Bb7
If you play by ear but hear only the standard diatonic chords, you will likely struggle when you get to the B section because those are not diatonic chords (at least in relation to the key of Eb). However, they are diatonic when you understand that the song changes keys twice during the B section. It goes to G major for 4 bars and then Bb major for 4 bars. Because Bb is the V of Eb, making that last Bb dominant allows the song to move right back to the key of Eb for the last A section.
The same thing happens in “Sleigh Ride” as well as other popular Christmas songs. Recognizing these key changes is fairly simple–look for non-diatonic chords that are not secondary dominants.