Diminished octave

Transcription

Hi! In this video I'm going to explain how to work out intervals for grade 5 theory. Are you ready? Let's go! First, you need to work out the interval number. To do this, you just count up the letter names. Here we've got A - B. That's two letter names, so this is a second. In this case we've got B - C - D - E - F - G - A. Seven letter names... this one is a seventh. If you have to count 8 letter names it's an octave. And if the letter name is the same but it's not an octave apart we don't say it's a first: this is a unison. Rule number one: intervals built from the tonic a major scale are always MAJOR or PERFECT the perfect intervals are the unison fourth fifth and octave.The major intervals 2nd, 3rd 6th and 7th. Here's an example The lower note is C so we're going to think of the C major scale The top note is F. This is a fourth above C so it's a perfect fourth because it's part of the C major scale. Here's another. G to F is seven letter names, so this is a 7th. Next to look at the G and we think about the G major scale F# is part of the G Major scale said this one must be a major 7th, But what happens if the top note is not part of a major scale formed by the bottom note? Here's an example. D sharp isn't found in scale of G major so what do we do? First of all, we need to remember that in the G Major scale the interval of G to D natural is a perfect fifth. D sharp is one semitone (half step) higher than that, which means that the interval is a little bit wider when the interval is wider than the one you would find in the major scale The interval is augmented so this interval is an augmented fifth. Now this interval look tricky but actually it's just as easy as the last one we just did First we need to look at the lower note, which is A flat, and then we need to think of the A flat major scale. Here it is: you can see that the sixth note in the A flat major scale is F. You need to remember that in the question we have F sharp, not F natural. This means that the interval has been widened by a semitone (half step). When a major interval is widened it also becomes augmented. This, is an augmented 6th. So now we know that when a perfect interval is widened by a semitone (half step), it becomes an augmented interval. What happens when the interval is narrowed by semitone (half step)? It becomes diminished. For example, here is a perfect octave. What happens if we change the top A to A flat? Because we flattened the A, we've made the interval narrower by one semitone (half step), so it's not a perfect 8ve now, it's a diminished octave. A major interval is increased by a semitone (half step), is also augmented. But a major interval can be narrowed by one or two semitones (or in other words) by a half step or whole step. When a major interval is narrowed by just one semitone (half step) it becomes a minor interval. If it's narrowed by two semitones (a whole step) it becomes a diminished interval. Here's an interval of a 3rd. We take the lower note, B, and think of the B major scale, which would be B, C# and then D#. In this one we've got D natural so it's one semitone (half step) narrower than the interval found in the major scale. So, this one is a minor 3rd. This time the D has been flattened so it's now two semitones (a whole step) narrower than the interval that you would find in the B major scale. So this one is a diminished 3rd. And here are all the 3rds that you could build from a bottom note B. B to D# is a major third because it's in the major scale. B to D natural is a minor 3rd, because it's on semitone (half step) narrower. B to D flat is a diminished third because it's two semitones (a whole step) narrower and B to D## is an augmented 3rd because it's one semitone (half step) wider. You also need to know about intervals that are bigger than an octave like this one. You can count these in two different ways. You can count from the bottom D to the top A which is 12 letter names, and call it a twelfth, or you can just count from D to A, which is a 5th and then use the word "compound". So this one is a 12th, or a compound fifth, and just as before you need to qualify the interval using one of the words "perfect", "major", "minor", "augmented" or diminished. So this one is a "perfect compound 5th" or a "perfect 12th". Here's a little exercise for you to practice what you you've learnt Pause the video and then come back and check if you were right. Interval a) is an augmented 4th. b) is a diminished 7th. c) is a major 6th d) is a minor 3rd and e) is an augmented unison. Did you get them all right? So far so good, but what if you can't make a major scale from the lower note? This could be because the lower note has a double flat or double sharp on it, or maybe you aren't very confident about making the major scale. Well: here's a trick you can use. The lower note G## here is much too difficult to build a major scale from so we're going to change each of the notes of the interval without actually changing the interval itself. We're going to lower each note by a semitone (half step). So the G## we'll lower to G#, and the B we'll lower to Bb. It's very important that you keep the SAME LETTER names when you do this. Now our lower note is G#, but this is still not a nice note to build a major scale from. So we're going to do the same thing one more time: we're going to lower the G# to G natural, and lower the Bb to Bbb. (Remember, you must keep the letter names the same). Now that the lower note is G, it's easy to work at the interval: think of the G Major scale. G to B is a major 3rd. G to Bb is a minor 3rd, G to Bbb is a diminished 3rd, so all of these intervals are diminished 3rds. We've now covered everything you need to know about intervals, so here's a quick summary First, work out the major scale from the lower note. If the top note is in that major scale, the interval must be perfect or major. If the interval is wider than the one found in the major scale it must be augmented. If it's narrower than a perfect interval it will be diminished. If it's narrower than a major interval, it'll be minor. And if its narrower than minor, it's diminished. An interval that's bigger than an octave is a compound interval, or you can just count all the letter names up to the highest note. If the lower note is too tricky to make a major scale from, then you can shift both notes up/down by the same amount keeping the letter name the same until you find a lower note you can make a scale from more easily.