Right thought id say a little bit about Intervals in general.
Lets start off by sayin that an interval is the gap or distance in pitch between two notes. It exists independantly of key signature etc etc, so an F# to Bb interval is an F# to Bb interval regardless of anything else.
It is always measured from the lower note to the higher note.
Interval descriptions contain two things:
1. The number of the interval
2. The quality of the interval
An example is a "major third", "perfect fourth", "diminished 6th" etc.
The "numbers" above are 3rd, 4th and 6th,
and the "qualities" are major, perfect, diminished,
As an example, lets take an easy one. We have two notes, lets say C and E. And we we want to determine the interval between the two of them.
(In this case, we'll call the C the lower note)
1. The number of the interval.
The number of the interval is calculated by going back to the very basics of notes.
Take the letters A B C D E F G and use these. Disregard completely any key signature, or accidentals or any of that and use the above list of notes to work out the number of the interval (Note: that is NOT the scale of A natural minor, its just a list of all the notes ever available for us to use within music)
So to get the number of a particular interval, for some reason, they thought it was a good idea to include both notes when counting, so countin up from C to E we get 3 notes: C D E.
Therefore, the interval from C to E is some class of a third
and indeed the interval from C quadruple sharp to E triple and a half flat is a third of some description.
When trying to work out the number of the interval, disregard any note descriptions (flat, sharp etc) or key signatures, and just take the names of the notes, e.g. C and E, F and G etc.
2. The quality of the interval.
What kind of third it is depends....in order for us to determine what type of
interval it is (or the interval quality
), we have to think in terms of a major scale with the root being the lowest note (regardless of what key we are in at the moment)
In this case, the root is C, so we build the major scale on top of that:
C D E F G A B C
we then work out whether or not our E note (remember?) fits into this or not. As you can see, it does, hence the C-E interval is called a Major 3rd
If our E not was actually Eb, it would obvoiusly not fit into the major scale of the lowest note. Therefore, the interval of C-Eb is a Minor 3rd
This is only applicable for certain notes of the scale however.
Below is a diagram about how semitone changes affect different intervals of a scale:
In a major scale, the notes that have perfect intervals from the tonic are always always always going to be: Unison/Octave (ie. the tonic), the 4th and the 5th.
The rest of the notes are obviously going to be Major intervals (i.e. 2nd, 3rd 6th and 7th notes.)
With a fundamental knowledge of major scales, we can read these off fairly routinely; e.g. if someone asks us what the interval from C to G is, we can quickly see that G is the fifth note of the scale of C major, and is indeed in the scale of C major, therefore the interval itself is a Perfect 5th.
The trouble arises when the higher note of the two is not found in the major scale of the lower note.
Now for an example
Lets take, for example, the notes C and Gb.
This could be any scale, any mode etc. (That is to say that the intervals of notes exist outside of concerns about key signatures etc).
And imagine that we are trying to work out the interval between the two.
Also imagine that Gb is the lower of the two notes (for fun!)
1. First of all lets get the Number of the interval:
Disregarding accidentals etc, we have G and C.
G A B C....which means that we're dealing with some class of a Fourth.
2. Now let's build a major scale from Gb upwards:
Gb Ab Bb Cb Db Eb F Gb
and wonder to ourselves "does the C note fit neatly into that?"...and of course it doesnt. We now think in terms of "what kind of a C notes does actually fit into the major scale of Gb?" and it'd be Cb of course.
So from the diagram above, the interval between Gb and Cb, both contained in the major scale of the lower (Gb) would be a perfect fourth.
BUT!! We dont have a Cb. Rather we have a C natural. In effect we are increasing the interval by a semitone, and from the diagram, what do we get if our interval is one semitone bigger than would otherwise be the case with a perfect fouth? As you can see its an Augmented Fourth
So to summarise:
1. Intervals are the difference in pitch between two notes.
2. They are measured from the lower note, to the higher note.
3. They exist outside of any concerns about key signatures.
4. They have both a number and a quality (e.g a 3rd that is major is called a major third)
5. To get the number, simply take the two note letters D, F , B etc and count up from the lower to the higher (including both in your count)
6. To get the quality, build a major scale on the lower notes, and see if the higher notes fits into this.
A. If it does:
i. and you have determined it is either an octave, 4th or 5th away from the lower notes, then its a Perfect interval.
ii. if the higher note fits into the major scale, but is not either a octave, 4th or 5th, then it is a Major interval.
B. if it doesn't:
then you have to consider what quality the interval would have had, if the note was in the major scale (such as the Gb C example above), and whether the note you actually have has made the interval bigger or smaller.
Consult the diagram thing above to figure out what effect making the interval bigger or smaller by a semitone has on your interval quality.
7. String the number and quality together, e.g (major 6th) and youre laughin!
Hope that helps, it was hard enough to explain, but its a start anyway!