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• In this lesson I’m going to talk a little bit more about perfect intervals.

• Now that you already know how to spell thirds and invert them

• the remaining intervals are going to be a lot easier to learn.

• Perfect intervals, abbreviated with a P, are going to include fourths,

• and fifths, and octaves, and I’ll even put this one down.

• A one would be a unison. I can’t play that one the piano

• because it’s the same note played twice so you need two different instruments to create unison.

• But it’s also considered perfect.

• First I’m just going to make a fourth, like this, and you might notice that

• it goes from a line to a space when you write a fourth,

• or it could be like this, from a space to a line.

• They have a really characteristic look on the staff.

• This first one, I’m going to keep the C where it is and I’m going to

• wrap the G around it and put it in the other octave, like that.

• And then I can just take that away. So I had that fourth and I inverted it into a fifth.

• So of course, 4 + 5 = 9, and we know that when we invert intervals we get nine.

• But what about the perfect part? It was perfect fourth and perfect fifth.

• It turns out that if something is perfect and you invert it, it is still perfect, so that’s easy to remember.

• So, perfect equals perfect when you invert it.

• Now let’s try a couple others that might involve some accidentals.

• Were just going to notate a couple of intervals here.

• Were going to start with a perfect fourth up, like this.

• So with this one, you can kind of think back about major thirds.

• Major thirds are just one half step smaller than perfect fourths.

• That means that if major thirds have four half steps, then perfect fourths must have five.

• That also tells you that if you invert a perfect fourth, that’s five half steps,

• youre going to get something with seven half steps because seven and five is twelve.

• With four half steps, sometimes people have all kinds of tricks for this.

• If you happen to know that F to A is a major third, you could just go up a half step,

• like this, a half step up from A is B flat, and that’s going to give you a perfect fourth.

• That's one way you can do it. But, you can also do it another way.

• You can count, F, G, A, B. So you know it's some kind of a B,

• and then you have to check how many half steps you have.

• So let's look at the piano. We've got our F, and then one, two, three, four.

• So if we just left the notes as they are, we'd get this sound.

• Now your ear might tell you that this is a really harsh sound, it doesn't sound like a perfect interval.

• That alone could tell you that something is wrong.

• Now we're going to go the way I first showed you.

• Let's say you happen to know F to A is your major third. I'm going to raise that up half a step.

• F to B flat gives me my perfect fourth.

• And then we can count. One, two, three, four, five. And there's the five half steps.

• We're going to look back up here and try a couple more.

• So I'm going to put my flat right here. There's my perfect fourth.

• We can start by counting. That gives me a C. Some kind of a C.

• Now, when I play this on the piano, it's going to sound very very dissonant.

• The nice thing about fifths, is two things. First of all, if one note is on a space, the other one will also be on a space.

• If one is on a line, the other one will be on a line.

• You'll get to know how they look, just like you know the way fourths look.

• I know I have them on the right place in general, but I'm just not sure about the accidentals.

• Well the other nice thing about perfect fifths is that they're usually going to have the same accidental.

• But not always, so we'll look at an example where that's not true.

• Usually they're going to have the same accidental.

• Now if you want to verify this to make sure this is actually right, there are a couple ways you can do it.

• Back over here on the keyboard, I had F sharp and the first thing I wrote was just a C.

• That's that really dissonant sound.

• F sharp to just a C natural. That's way too dissonant for a perfect interval.

• Then I thought they usually have the same accidental in front of them, right?

• F sharp to C sharp. Now we can count, one, two, three, four, five, six, seven.

• Seven half steps, and I know that has to be true because a perfect fourth has five

• five plus seven is twelve. Let's look at it in one more way.

• I'm going to invert this and make sure that it inverts to a perfect fourth.

• I'm going to keep my F sharp the way it is,

• and I'm going to take that C sharp and move it down to the previous octave.

• That sounds like a perfect fourth, but I want to make sure.

• One, two, three, four, five. Five half steps.

• I'd rather count five half steps than seven half steps.

• So if I'm going to count, I'm going to count the inverted interval,

• and then invert it back to where it was.

• We're going to look at an example where a perfect fifth doesn't have the same accidental

• kind of like the perfect fourth over here,with two different accidentals.

• Let's try this one.

• Now I'm going to try to write a perfect fifth down from F.

• It turns out that when you're writing fourths or fifths, and you're using these notes F and B,

• you tend to get some funny things that happen.

• The reason for that is that the keyboard is not symmetrical.

• There are, as you remember on the white keys of the piano, there are half steps between

• B an C, and E and F, and all the other ones have whole steps.

• That means that even though something might be true in one case, like the two sharps here,

• it's not going to be true in every case, because the keyboard is not symmetrical.

• Let's look and see what happens here.

• I know they're both supposed to be on the line, because that's how perfect fifths look,

• so instead of counting, I can just go like this. Skip that line in the middle.

• I can always count if I need to verify if that's a fifth, but I know that it is.

• Now this one has got a B and an F in it, so when I play it on the keyboard,

• because I know about the keyboard, I know it's going to sound really dissonant.

• Let's see if that's true.

• Here's the F, and if I walk down, one, two, three, four, five,

• there it is. So this is not a perfect fifth. It's very dissonant sounding.

In this lesson I’m going to talk a little bit more about perfect intervals.

A2 初級

# 音樂101：完美的間奏 (Music 101: Perfect Intervals)

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songwen8778 發佈於 2021 年 01 月 14 日