We are done!

We have described all the major rules of music! We know the name of each tone in music, and we can even calculate its frequency. We know how to create scales, chords, and what intervals are. Let's try to answer some tricky questions!

Can a frequency of 450 Hz occur in music?

No, because the first tone is 27.5 Hz, it doubles each octave (55, 110, 220, 440 = A4), and there must be a 6% gap between consecutive tones, so the nearest tone would be A#3 with 466 Hz.

Can tones C, C#, and D occur in one song?

No, because a song must use a specific major scale, and a major scale never contains three consecutive tones.

Can both D# minor and D# major chords occur in one song?

The C major scale never contains a minor and a major chord of the same root tone. Every other scale is just a "shifted" C major scale, so it must be true for every scale (the answer is No).

A musician played the D major chord; could his song be in the key of C (C major scale)?

No, because the D major chord contains a tone F# (black piano key), while only white piano keys are allowed in the C major scale.

A singer sings tones of C, E and F in the key of C major. Can I sing along, but a fifth higher (7 semitones)?

Yes. From C we get G, from E we get B, and from F we get C (all three are in C major). Also, 7 semitones ("the fifth") is the next most beautiful interval after 0 (unison) and 12 semitones ("the octave"). Major and minor chords contain this interval.

Building a Song

When creating a song, we must choose the scale, e.g., the C major or the F# major. This step "deletes" 5 out of 12 tones from each octave (we can't use them). We can write down the six chords, which are allowed to be used in our scale, and arrange them into a repeating pattern. If we decide to sing or play some interesting melody with a new instrument, we must still obey our scale (and the current chord, if possible).

There is no need to follow all these rules precisely! You can always try to break a few and see what impression it gives. If we add just one more tone to our scale, we can play a few new chords! E.g., if we add G# to the C major scale, we can play the E major chord and the F minor (8 chords instead of just 6).

You can create or record any sound or any noises and call it music, as long as you can find people who like it :)