Sound 3, Sound 4, Sound 5, Sound 6: Flexibility and Limitations.
So these voicings have largely been used as a slash chord over bVII/I. There are 6 Sounds that fullfil this slash chord idea to produce extensions that start out as tonal and progress from S1 to S6 through to stronger colored extensions, or if you will: an increase in V7 harmonic pressure. There are possible implications of a system that I won't get into but it can be figured out with a look at how these 'Sounds' (S) become progressively colorful or urgent in their respective strength in terms of being compelling. There is a fundamental basis for this such as it is.
Using the example of G7, this is the proposed order from Tonal through Chromatic
S1: FS1 = FMa7(b5)............. so FS1/G = G13
S2: FS2 = FdimMa7............. so FS2/G = G13(b9)
S3: FS3 = F7(b5).................. so FS3/G = G9(b13)
S4: FS4 = Fmi7(b5).............. so FS4/G = G7(b9b13)
S5: FS5 = FMa7sus4(b5)...... so FS5 = G13(#9)
S6: FS6 = F7sus4(b5)............so FS6 + G7(#9#5) or (#9b13).
S1 through S6 in a comparative viewpoint of a tritone and the tritone slash/chord roots with information on similarities, inversion, scale/chord and other similarities or contrasts:
S6: S6 (7sus4[b5]) and S1(Ma7[b5]) in relation:
It can be seen that FS1 and BS6 have the same structure i.e the same notes respectively: (FABE) and (BEFA). The opposite view is also true: FS6 (FBbCbEb) i.e. (F7sus4[b5]) = BS1 (BD#FA#) i.e. (BMa7[b5]). They have a tritone relation. Notice that while G13 and Db7(#9b13) share the Same FS1 chord. The FS1 used in the Db chord (on the third above the Db root) makes it Db7(#9#5). If this 'F' Sound chord (FABE) is inverted to its 2nd inversion (BEFA) the 'root' position it can be seen as BS6/Db rather that FS1/Db. So there is a polarity going on there between tritone opposites. The FS6/BS1 line up the same way only with opposite roots.
S5: (Ma7sus4[b5]) when inverted to 2nd inversion, shares the same 7th chord quality with tritone opposite roots:
FS5 i.e. FMa7sus4(b5) when inverted to 2nd inversion creates the same quality, intervallic structure, and the same notes— a tritone away i.e. BMa7sus4(b5). On one hand we have a G13(#9) [FS5/G] and on the other we have a Db13(#9) [BS5/G]. It is significant to note that FS5 and BS5 share the same diminished scale (W—H) i.e F G Ab Bb Cb Db D E—B C# D E F G A A#....
S4: i.e. (mi7[b5]) is used on bVII to create a V7(b9b13):
Although FS4 and BS4 appear in the same Symmetrical DOMINANT (H—W) scale (over F7 or B7 [also Ab7 and D7]) but that doesn't apply here with S4 because when it is used as a bVII/I it creates chords that are consistent with the Symmetrical DIMINISHED scale but ARE consistent with the ALTERED Dominant scale, and the Harmonic Minor Dominant scale, i.e. this V7 chord will use a b13 and b9.
FS4 i.e. Fmi7(b5) shares a tritone with BS4. Both these sound chords have the same quality when placed over the appropriate root (bVIIS4/I) i.e. FS4/G = G7(b9b13) and BS4/Db = Db7(b9b13). In this case it's not particularly significant that Fmi7(b5) and Bmi7(b5) share the same Symmetrical Dominant scale as it doesn't apply in this case. The altered form of the scale is a chord scale that will respectively work well with each of these chords i.e. G7 Altered (mode VII of Ab Melodic minor) and Db altered as mode VII of D Melodic minor. In the graphic below note that FS4/Db = Db9 and that BS4/G = G9. So there are two opposites of color included in this case (as is S1 and S6).
S3: is a symmetrically inverted chord between root position and 2nd inversion:
For example, F7b5 when inverted to 2nd inversion results in a B7b5. At first look it looks like it might appear in the Symmetrical Dominant (H—W) and does, but it doesn't apply in this case. We are looking at G7 chords and Db7 chords. If S4 were to be used in a dominant scale/chord this way, the roots of the V7 chords would be F7, Ab7, B7, and D7. But, again as in S4, the chord created as a bVIIS3/I, using our examples: G9(b13) and if FS3 (F7(b5) is inverted to a B7(b5), as BS3/Db, the chord has the same quality on its tritone root (G): namely Db9(b13).
S2: has been laid out in the previous blog.
S2 is the most versatile 'Sound' chord in a way because it does reside in the Symmetrical Diminished scale at 4 evenly spaced minor 3rd intervals. FS2 then, can be over a G root = G13b9, a Bb root = Bb7(b9#11), a Db root = Db7#9, and an E root = E7b9. S2 also occurs in mode 4 of Harmonic Major (in C: CDEFGAbBC).
S1: Look at S6 and reverse the tritone opposites and the same situation occurs.
FS1 = BS6, and BS1 = FS6. When these are placed as a bVII/I, the resultant chords are the same.
FS1 (Fma7b5)/G = G13, BS6 (B7sus4(b5)/Db = Db(#9#5)....... the 'S' content of each chord contains the same notes: FS1 (FABE), and BS6 (BEFA). BS6 is the 2nd inversion of FS1.
FS6 (F7sus4[b5])/G = G7(#9#5), BS1 (BMa7b5)/Db = Db13.......The 'S' content of each chord contains the same notes: FS6 (FBbBEb), and BS1 (BD#FA#). FS6 is the 2nd inversion of BS1.
Here is an overview: