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Thread: tri-tone in a V7?

  1. #1
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    tri-tone in a V7?

    I am reading through a music theory paper i printed out on line (i think i got the link from this site) and it is talking about the tri-tone being in a V7 chord, so for example in the key of C that would be a G7 chord. It is talking about this making it unstable and wanting to go back to the 1 chord.

    The notes of the G7 chord unless i am getting lost some where are G B D and F.

    As far as I was aware the tri-tone is an Aug 4th or a gap of 6 frets.

    G + 6 frets is c sharp so it is not in the chord
    C + 6 frets is F sharp so it is not from the oringinal key scale either.

    am i lost somewhere or is the info wrong? (i think it is probably my understanding of 7 chords)

  2. #2
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    Yes, the notes of a G7 chord are G B D F.

    The tritone occurs between the third and (flatted) seventh - the B and F notes.

    The "pull" towards the I chord (C in this case) occurs from the B moving a half step to C (the root of the I) and the F moving a half step to to E (the third of the I).

    You can read some more here.

  3. #3
    Registered User Malcolm's Avatar
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    Quote Originally Posted by Mr Phil View Post
    ..........It is talking about this making it unstable and wanting to go back to the 1 chord.
    I would not have used the word unstable, but, that is a good definition of what has happened. I like better -- any time you add the b7 you increase the tension, therefore that G7 has reached a higher level of tension, anything other than resolution to the I tonic chord would be anti-climatic. You've reached climax, close it out and move on to the next phrase, verse, whatever. That's why I call it the climax chord.

    Dominant seven chords are inserted incorrectly IMO all the time, especially in Country, Blues and Rock, i.e. they are not reserved only for the V dominant chord placement by many songwriters. My theory of why this happens - which is easier to make; Amaj7 or A7? As a matter of fact the A7 is easier to make than the triad A chord. Then there is the blues progression with all dominant seven chords, so when to use the dominant seven becomes a good question. I think of it being a climax chord and to be used just before ending a phrase by resolving back to the tonic I chord. That seems to simplify when to use it. Of course IMHO. Check out what is said here; http://guitarteacher.wordpress.com/2...rds-on-guitar/

    Basic Chords
    • Major Triad = R-3-5
    • Minor Triad = R-b3-5
    • Diminished Chord = R-b3-b5

    7th Chords
    • Maj7 = R-3-5-7
    • Minor 7 = R-b3-5-b7
    • Dominant 7 = R-3-5-b7
    • diminished = R-b3-b5-b7
    • Full diminished = R-b3-b5-bb7

    For the rest of the story ..... http://www.smithfowler.org/music/Chord_Formulas.htm
    Last edited by Malcolm; 10-15-2012 at 05:22 PM.

  4. #4
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    That is great info, thanks.

    Never occured to me to compare the internal intervals and not just the root of the chord/scale. It now makes total sense.

    Phil

  5. #5
    Registered User JonR's Avatar
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    The cool thing about tritones is their ambiguity. When we hear one - with no context - it could be either a #4 (augmented 4th) or b5 (diminished 5th).
    Eg, if we hear this:

    ---------
    -3--------
    -1--------
    ---------
    ---------
    ---------

    - how do we know whether it's G# and D, or Ab and D? As G#-D (diminished 5th) it resolves inward like this:

    ---------
    -3->-2------
    -1->-2-----
    ---------
    ---------
    ---------

    ie, to the root and 3rd of an A major chord. (Because G#-D is 3rd and 7th of E7.)
    But as Ab-D (augmented 4th), it resolves outward like this:

    ---------
    -3->-4------
    -1->-0-----
    ---------
    ---------
    ---------

    to the root and 3rd (inverted) of an Eb major chord - because Ab-D is 7th and 3rd of Bb7.

    This dual identity of the tritone is what enables the jazz "tritone substitute". It means we can use Bb7 to resolve to A or, likewise, E7 to resolve to Eb.
    IOW, the "tritone sub" is based on the shared inner tritone in both chords, which is the active interval, not just the tritone root difference (although most people remember it as the latter).

    Here's how it works in A major:

    Bm7 Bb7 A
    ------------------------
    -3---3---2-----------------
    -2---1---2-----------------
    -4---3---2-----------------
    -2---1---0-----------------
    ------------------------

    Check out all those half-step moves. That's a lot cooler/funkier than the classical Bm7-E7-A.

    You don't only get it in jazz; it can happen a lot in blues too. Eg, if you're in the key of A, and move to the D9 chord by sliding down from Eb9, the Eb9 is (in theory) a tritone sub for A7.
    And when you end the song with a Bb7-A7 move (instead of the too-cute E7-A7), you're using a tritone sub.

  6. #6
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    Thanks Jon! that that is really very interesting stuff and i am trying to get my head around it.
    Not near an instrument at the minute but going to mess about with it tonight and try and get it straight in my head.

    Phil

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