How to work out Compound Intervals!

The final stop on our intervals journey… what if my interval is larger than an octave? How to work out a compound interval!

So far we have learnt how to work out the distance between two notes, whether the interval is major, minor or perfect. Then we introduced the idea of diminished/augmented and in the last post we looked at what to do if we don’t know the scale of our bottom note. 

But what do we do if our interval is larger than an octave (8 notes). There are two ways to approach this…

Compound Interval – Method 1

We can simply continue counting on! 

What is the distance between these two notes?

That’s correct… the distance is a 13^th! 

Now we simply ask ourselves the same question…

Is E natural in G major?

Yes! E natural most definitely is in G major. 

This makes this interval a MAJOR 13^th

However, this is not the only way to describe this interval. Another way of looking at this involves using the word ‘compound’

compound interval – method 2

A Compound interval is simply ‘larger than an octave’. 

Let’s look at the interval above again…

This interval would be far easier to work out if the E was an octave lower… so let’s put this interval back to its simple state i.e. E one octave lower to make the total distance in the interval less than an octave. 

Much nicer! What would this interval be?

That’s correct, it is a 6^th! Is E natural in G major? Yes it is! 

So this is therefore a major 6^th!

Now let’s look at the original interval..

It is larger than one octave. In order to make this work we can call this a Compound Major 6^th!

So as you can see there are two different ways to label an interval larger than an octave. This can be literally naming the distance between the two notes (9^th, 10^th, 11^th etc) or working out what the interval would be if it was smaller than an octave and then writing the word ‘compound’ in front of it! Both ways mean the exact same thing. 

One important thing to consider though is which intervals will be perfect and which will be in the major/minor category? 

In our intervals below an octave, we know the 4^th, 5^th and 8ve intervals are perfect. Now if you are using the ‘compound’ method then this rule still applies – easy! 

If you use the other method where you are simply counting the complete distance then you must remember that the intervals of an 11^th and 12^th will be perfect!

Let’s try a few examples…

What interval do we have here? 

Let’s use Method 1 (finding the literal distance between the notes)

The distance between these two notes is a 12^th! Is C natural in F major?

Yes it is! But remember if we have an interval of a 12^th this will be PERFECT! So the answer to this question, using method 1, is a perfect 12^th! 

What about this one?

Let’s use Method 2 for this one! 

Firstly, let’s bring this interval to it’s simple state

That is now much easier to work out! What is the distance between these two notes?

That’s correct, it is a 6^th. Is C double sharp in E major?

No it’s not, but we do have a C sharp! C double sharp is just one semitone larger than C sharp, making this interval an AUGMENTED 6th.

Now don’t forget the word compound… and your final answer is:

Compound Augmented 6th!

I hope that has made this quite confusing topic a little clearer!

See you soon!

Jade x