A Tonic Note is always in the case of a Scale:
A tonic note, in conjunction to a scale, is that note which has the lowest pitch (frequency) in any octave of that scale. It is the first note of that scale upon which the scale is named.
A root note is always in the case of Chords:
Take for example the C major scale. Its tonic in the C note and its notes are:
C D E F G A B c
The C major chord is thus formed by the notes, C E and G
Thus the root note of the C major chord is the C. The final note is the C of the next octave (written as "c") and is hence of twice the frequency of C. This is why the first C is the root note and not the last one. The concept will be clearer if we used scientific pitch notations (please read before reading this).
In the diagram above, four octaves have been shown, viz. C4 to C5, C5 to C6 and C6 to C7. Let us take the example of C major again. Since we are dealing with the key of C, in order for us to fit one entire scale of C (major), we need to start our octave from a C note. So, we take the octave C4 to C5. The notes here are -
C4 D4 E4 F4 G4 A4 B4 C5
Comparing with the C major scale written out above, we see that "C" = "C4" and "c" = "C5." As the frequency of C5 is twice that of C4, the lowest pitched note in this octave starting at C is C4 ("C" of above). Thus the "root note" is C4 ("C") and not C5 ("c") when we play the C major chord using middle C (C4).
Similarly, if we have the scale of C minor, the notes will be:
C D Eb F G A B c
and the C minor chord has the notes C Eb and G. Even here the tonic note for the scale is C and the root note for the chords is the pitch, C.
Again in the case of C7 chord, the notes are:
C E G Bb(just adding the dominant 7th interval's note with respect to C - Bb)
Again the root note remains C for the C 7 chord.
Thus we state an obvious fact here - the root note depends upon the scale we choose and the scale we choose determines the lowest note that is played in that scale.
Cond....Root note and misconceptions
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