Regarding piano scales,are diminished sevenths and dominant sevenths the same thing?

Question

and if not what is the difference?and also what are harmonic intervals?Thanks a lot.

Answer 1

In the interest of clarity let's build the chords starting on G and stacking thirds:

G major chord - G, B, D

Adding a minor 3rd above the G chord gives you a G dominant 7th:
G Dom. 7th - G, B, D, F

By lowering (diminishing) the interval of the top three notes by a half step you have a diminished 7th chord:

G dim. 7th - G, Bb , Db, Fb
You will note that the interval between each note of the chord is a minor third.

Now let's build the same chords starting on C:
C maj. chord - C, E, G
C dom. 7th - C , E, G, Bb
C dim. 7th. - C, Eb, Gb, Bbb (B double flat)

These chords can be built starting on any note. Within the context of a single scale the Dominant 7th would be built on the 5th note of the scale (Key of C: GBDF). The diminished 7th would be built on the 7th note of the scale (Key of C: B,D,F,Ab).

A harmonic interval is the vertical distance between notes of a chord (stacked notes).

A melodic interval is the vertical distance between notes of a melody.

The sound of the Dom. 7th and dim. 7th chords cause them to function as strong progression chords. The Dom. 7th generally leads to a resolution on the tonic (I) chord of the scale. Due to all the tendency tones in the dim. 7th chord its direction of progression is rather ambiguous and is not apparent until its resolution, thereby making it the most versatile chord to use for modulation since it has a huge number of possible interpretations.

Musician, composer, teacher.

Answer 2

1st, you mean chords, not scales, right?

A dominant seventh chord is built on a major chord, with an added minor seventh above the root. (Major third, minor third, minor third) It occurs naturally on the 5th degree of a major scale. A diminished 7th is made up of three consecutive minor thirds, and does not occur naturally in either a major or minor scale, although it is often used as a substitute for a dominant 7th.

A dominant 7th has really only 1 resolution, to the tonic. Sometimes it will resolve to the submediant, but that is considered an exception to the rule. (It can also be respelled as an Augmented 6th chord of the German variety, but then it is no longer a dominant 7th).

A diminshed seventh chord, being symetrical, can be resolved in many ways, since each note can be considered a root or a leading tone, depending on how you spell it. For fun, if you drop any note in a dim7 down a half step, you get a dominant 7th of some sort. If you add a note a major third (or tenth) below any of the chord members, it becomes the root of a dominant flat 9th chord. Enharmonically, there are only 3(!!) diminished seventh chords on the keyboard.

Stop me, or I will turn into a real theory geek on you.

EDIT:

Thank you , troz99 for noticing that gaff!! It has been corrected.

Answer 3

Add Mira and Nelly's answer together and you'll have a pretty good definition. A small correction on Nelly's answer for the diminished aspect. An Ab is a diminished 7th above B not a minor seventh above.

There are two ways to spell chords. Stacking thirds or building them off the notes in a scale. Both have pretty much already been explained.

Answer 4

Okay, first the easy one to explain: a harmonic interval is an interval in which the two notes are played at the same time. Melodic intervals are played one note after the other.

Secondly regarding dominant 7ths and diminished 7ths:

First off, they are not scales, they are chords.

A dominant 7th is the dominant chord of a given key (ex. C major dominant chord would be a G chord because G is the 5th note, or dominant, of the C major scale) with the note which is a minor 7th above the root of the chord being added to it (ex. a C major dominant 7th chord is G-B-D-F. G-B-D being the dominant chord, F being the added 7th)

A diminished 7th chord is built on the 7th note of the scale, so you'd start with the leading tone triad, and then add a fourth note which is a minor 7th above the root of the chord. (ex. c minor diminished 7th chord is B-D-F-A flat, B-D-F being the leading tone triad (which is a diminished triad BTW, because the third of the chord is a minor 3rd above the root, and the 5th of the chord is a diminished 5th above the root), and then you'd add the A flat, a minor 7th above the root of the chord.

EDIT: Thank you troz99 :-) You are correct.

Some days I'm brain-dead in the morning:-P

Answer 5

Not quite. A dominant seventh is built on the 5th (dominant) degree of the scale, whereas a diminished seventh is made up of three superimposed minor thirds.

The diminished seventh chord is used mainly in late classical music, particularly baroque and renaissance, whereas a dominant seventh is used more frequently, mainly in standard compositions.

Harmonic intervals are tones, i.e. the distance between notes. For example, from middle C to E in the key of C major is a third, because it is the third note (C, D, and E) and will sound harmonious. If, for instance, you were to play a seventh, say from C to B, it would not sound harmonious or melodic, but would sound "unfiinished". This would therefore be a major 7th, but not a harmonic interval.

Without knowing how advanced you are, I'll end here, because I'm in danger of becoming too technical. I do hope I've been of some help, and enjoy your studies.

Answer 6

There's not much to add to Nelly's answer. Although Mira is right on the actual notes (g-b-d-f) her explanation is wrong.
Why?
A chord is not build on thirds, like Mira's example
> No. Dominant seventh is built up from a major third,
> then a minor third and then again a minor third (ex. G-B-D-F in C-major)
but it's build bottom up.
So
first a major third (G-B)
Then a Perfect fifth (G-D)
and finaly a minor 7th (G-F)

You get the same notes, but the idea is different. A chord is like a building build ed on it's root.

Now back to your question. You could add a 9th to this chord so we get G-B-D-F-A(flat) This is the dominant 9th chord. Now there are several people who claim that a diminished 7 chord is actually a dominant 7 with missing root. B-D-F-Ab
This is right when you look at it's function. Like the G7 chord it resolves to a C chord but it seems to be in contradiction with the fact that a chord is build ed on it's root like stated before. in reality however the chord will often resolve indirect like this
1) b-d-f-ab
2) b-d-f-g
3) c-e(flat)-g

That's why people look at it as a dominant with missing root.

B.t.w. There are plenty of examples in Baroque and Classical music of the diminished 7 chord.
Only from about the late classical period (Beethoven) composers discovered the full potential of the chord.
f.a.
b-d-f-ab belongs in the key of c
b-d-f-g# belongs in the key of a
cb-d-f-ab belongs in the key of eb
b-d-e#-g# belongs in the key of f#

all these chords sound the same but can lead to very different directions
/*********************
Edit to Glinzek
> Enharmonically, there are only 3(!!) dominant seventh chords on the keyboard.
You mean only 3(!!) diminished seventh chords in your otherwise excellent explanation

Answer 7

No. Dominant seventh is built up from a major third, then a minor third and then again a minor third (ex. G-B-D-F in C-major) and one should built that on the fifth note of every scales, so on the dominant. It exists in major and minor
scales naturally. While diminished seventh exist naturally only in the harmonic minor scale, and started on the seventh note of that (ex. G sharp - B - D- F in a-minor). It consists of only minor thirds.

Regarding harmonic intervals, they are like thirds, fifths, and so on. But I don't like to bore you with my poor English. Look at that:
http://musiced.about.com/od/lessonsandtips/f/harmonicinterva.htm
Hope it helps.
mira

EDIT:
Hey,
Nice to see, that some of you have read my answer, too. Thanks, for taking time for that. :-)
Of course my answer above is not an explanation of the chords theoretically (I wouldn't even attempt to do that without any knowledge about the asker's qualifications in music), it's only an easy description technically/pragmatically, that everybody can understand and try on a piano, who knows the intervals. If the asker would be interested in ex. what "sixte ajoutée" is, then I would be in trouble with this method, for it couldn't be described in such an easy way (I mean without explaining Rameau's theory on that or at least something about inversions and why that is not that primarily...) I thought that the goal here, was that to give as easily understandable answers, as we can. But, thanks for correcting me, again.
mira

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