Trying to figure out the key for soloing

To start with, one of the chords is going to be the tonic chord in the key. With Am7-Dm7-Em7, you won't be in F# or Bb or whatever... you'll be in Am, Dm, or Em.

So look at where those chords would fall in each of the keys:

Am: i-iv-v
Dm: i-ii-v
Em: i-iv-vii

Since most rock/pop/blues tunes are built around a I-IV-V progression, you're almost certain to be in the key of Am.

What scale you use is up to you. The Am pentatonic has notes A-C-D-E-G, which fits pretty nicely... all three chord roots are there, as are all four notes of the Am7 chord, and three notes each of the other two chords. You're not very likely to hit a 'bad' note.

Thanks NoteBoat, I tried Am Pentotonic and it fits very nicely. I was looking at the notes of the respective chord:

Dm7: D-A-C-F-A
Em7: E-B-D-G-B
Am7: A-E-G-C-E-A

And it seems like it got every note in the C Major scale. But C Major scale does not work, especially notes like E, F, G, B, C does not harmonize well with the progression (to my ear, so I may be wrong). Why?

I thought the idea of finding the right key for solo is to use the scale that doesn't have any note fall outside of the key, say for instance above, any other key other than C should not be used. But I am wrong, apparantly. I don't understand what other consideration should I be doing?

Thanks, CJ

Well, the C major scale will work (as will lots of other scales)... but it depends on your note choices.

See, each chord has consonance or dissonance with different tones. If the note you're playing in your lead happens to be in the chord, you have consonnance - they 'agree' with each other. If a note isn't in the chord, you have complex relationships between the melody and the chord notes.

Let's say you're playing an E note over the Dm7 chord. You're now hearing these intervals:

D-E = major 2nd
F-E = major 7th
A-E = perfect 5th
C-E = major 3rd

Now let's see what happens when you play B over that chord... you've got:

D-B = major 6th
F-B = diminished 4th
A-B = major 2nd
C-B = major 7th

Because of that diminished interval, the B note will sound more 'tense' over the Dm7 than the E note will. Each non-chord tone will have its own set of relationships, and more or less tension than other notes.

Over time, your ear becomes attuned to these relationships, and you start to use the dissonant tones to craft intersting melodies - ones that have tension and release, raising dissonances and logically resolving them to consonances. But when you start to solo, it's more of a 'hunt and peck' approach... you're not hearing in your head what the sound will be yet, you're just choosing a note from a fingering pattern you know.

That's why scales like the pentatonic are so useful in beginning to improvise - you won't have too many notes that aren't consonant. Using a simple scale makes it harder to make a really interesting melody... but it also makes it harder to create a 'bad' one. You'll notice that E is in the pentatonic scale, but B isn't :)

One other thing is the choice of tonal center. Although all the notes are in the C scale, all the chords are minor. Playing/thinking in A minor will get you better results than playing/thinking in C. That's because you'll land more phrases on A when you think in A minor, and A is:

the perfect fifth of D
the perfect fourth of E
the root of A

If you think in C, you'll tend to land phrases on C, and you end up with:

the minor seventh of D
the minor sixth of E
the minor third of A

Since perfect intervals sound more resolved than others, your solo will sound more 'finished' or 'intentional' if you center it around A instead of C. So when you do 'graduate' from the pentatonic to the major and minor scales, you'll find A minor works better than C major.