Can someone explain what it means 2 bar turnaround that marks the end of each chorus cm7 eb7 ab7 g7. I understand 12 bar blues for the most part however I am unclear when I see this in learning material.
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Hey Lisa - welcome to the forum! Happy to have you here. I changed the title of your post to “What is a turnaround” and put it under the “Theory” category. I hope you don’t mind.
So did you have a photo or a link in your original post. If so, I’m not seeing it? Anyways, it looks like you’re working on a Blues in Cm, and you have a 2 bar turnaround that has 2 chords per bar. This is gonna be a little journey to understand where those chords are coming from, so grab a cup of tea, and bear with me here…
A “Turnaround” loosely speaking is some kind of chord change at the end of the tune that creates tension which is resolved by returning to the “Top” of the tune. And so it kind of “turns us around” back to the beginning of the song.
Different songs can have different types of turnarounds. In the 12-Bar blues, the turnaround typically refers to the last 2 bars of tune (meaning bars 11 and 12 of the form.)
In it’s most basic from, the LAST FOUR BARS of the basic 12-bar blues are:
V - IV - I - I (which would be G7, F7, C7, C7 in Blues in C.)
However ending on the I chord doesn’t create any tension that “turns us around” back to the top of the tune, so the most common alteration to this basic blues is to end the last bar on the V chord instead of the I chord, so that now the LAST FOUR bars of the tune are:
V - IV - I - V (so in the key of C these chords would be G7, F7, C7, G7)
To be clear, the TURNAROUND here is one bar of I (bar 11) followed by one bar of V (bar 12.) One chord per bar. Four beats per chord.
Now the Jazz world of course is never satisfied simplicity. So to go from a standard 12-Bar Blues to a Jazz 12-Bar Blues there are a lot of harmonica variations throughout the form. For example, bar 9 replaces the V with the ii, and bar 10 replaces the IV with the V.
Notably, for our discussion, the turnaround is one of the places that gets some real spice. Instead of one chord per bar, we now have two chords per bar (each chord lasting two beats.) So the LAST FOUR BARS of the most basic Jazz 12-Bar Blues is:
ii - V - I vi - ii V (in the key of C that is Dm7 | G7 | C7 Am7 | Dm7 G7)
So the BASIC JAZZ TURNAROUND is:
I - vi - ii - V (In the key of C this is is: C7, Am7 | dm7 G7) Again, important to realize that each chord is getting only 2 beats in this version of the turnaround.
As our German friend @AstridHandbikebee63’s link shows there are a ton of common ways that Jazzers like to vary these changes. Here are a few of the most common:
I VI - II V (In the key of C this is C7 A7 | D7 G7)
III VI - II V (In the key of C this is E7 A7 | D7 G7)
I VI - bVI V (In the key of C this is C7 A7 | Ab7 G7)
I bIII - II bII (In the key of C this is C7 Eb7 | D7 Db7)
There’s an almost infinite way that you can vary this progression, and here’s a couple of the most important concepts in understanding where the variations come from:
PRINCIPLE #1.) Understanding the BASIC HARMONIC FUNCTION of various chords.
The TONIC function is like “home base” for the key, a feeling of resolution. The chords that fill this roll are I, iii, and vi (so in C that’s C, Em, and Am. Or in C blues C7, Em7, Am7)
[That’s why the simple jazz turnaround, bar 11, instead of just being C, now has C and Am. because they have the same harmonic function of being the TONIC chord.)
The DOMINANT function is “creating tension” or “asking the question” that wants to be answered by the reolsution of the Tonic chords. These cords are
V and vii (so in C that’s G and B diminished, or in C blues it’s G7 and Bm7b5)
The SUB-DOMINANT function are the chords that are intermediaries. They don’t create as much tension as the Dominant chords. Rather their primary function is to LEAD us to the Dominant chords. These chords that fill this roll are ii and IV (So in C they are Dm and F, or in C Blues, Dm7 and F7.)
[That’s why in the simple jazz turnaround, in bar 12 instead of just having G7, we have 2 beats of Dm7 which then pulls us to the G7 for 2 beats, which then pulls us back to the tonic C7 at the top of the tune.]
PRINCIPLE #2.) DOMINANT 7TH CHORDS: In Jazz any of the chords that are naturally minor, may be made Dominant 7th cords (i.e. what are naturally Dm7, Em7, and Am7 now become D7, E7, and A7.)
Turning the minor 7th chords into dominant 7th chords INCREASES THE TENSION and pull to the chords that they are resolving to. So a Dm7 wants to pull to a G7. But a D7 wants to pull to a G7 WITH EVEN MORE ENERGY or TENSION. Similarly, an Am7 wants to pull to a D7, but an A7 wants to pull WITH EVEN MORE ENERGY or TENSION.
PRINCIPLE #3.) TRITONE SUBSTIITUTIONS: In Jazz, on any Dominant 7th chord that is resolving to a TONIC chord, you can substitute a Dominant 7th chord whose root is a tritone away. “Tritone” is the note between a 4th and 5th. (I can explain the “why” behind this but feel this post already has overwhelming amount of info, lol.) So here are tritone substitutions for dominant 7th chords in the key of C:
D7 becomes Ab7
E7 becomes Bb7
G7 becomes Db7
A7 becomes Eb7
So I think now we can finally kind of see where the 4-chords that are in your turnaround are coming from. Looks like you’re playing a Cm blues, so a typical jazz turnaround would be:
I - VI - II - V (autocorrect wouldn’t allow me to do a lower case I, lol) which would be Cm A7 D7 G7, and then making our Tritone Substitutions:
The A7 becomes the Eb7
The D7 becomes the Ab7
And presto we have Cm7 Eb7 Ab7 G7.
And that my friend is where you turnaround is coming from. Hope that helps. LMK if you have any questions?
Rock on,
Luke
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Luke… Thank you for the lengthy education on the turnarounds and so sorry it took me so long to respond. I was on vacation. I will have to read this few times to digest. but I get the gist. I am really enjoying your forum and learning material I purchased on line. In the meanwhile I will explore the forum more for my questions. Best to you. Lisa
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Astrid… Thank you for the information on turnarounds I don’t really understand for I don’t know german. however thank you for taking your time. Lisa
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Hey Lisa - right on. Yes, don’t hesitate to ask as many questions as may pop up for you. Any questions you have, guarantee others will have too. That’s one of the great things about our dialogues here on the forum - everybody gets to benefit from it.
Happy harpin’,
Luke
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Hi Lisa. If you copy the text, and paste it into the Google search bar, it’ll usually decide for itself that you want it translated. 
To Luke- that’s a great explanation, until recently when I bought a sax, I had no idea about jazz music at all. This explanation is invaluable!
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