When a diminished triad is being made in the root position, it may be changed to a minor triad by raising the upper note by a half step (one fret). If a minor triad is made in the root position, it may be changed to a diminished triad by lowering the upper note by a half step (one fret).When we get into 7th chords, a full diminished seventh chord consists of the diminished triad and the diminished seventh interval. Some write the symbol as Cdim7, others use Co. The little zero should be raised up.
Again if you need more information on intervals view lesson #1447 Intervals.
The 7ths used on chord symbols normally consist of the Major 7th interval and the minor 7th interval. Chord symbols respectively "maj7" and just the plain numeral "7". We also use a diminished 7th interval in the chord. The diminished 7th interval is the enharmonic equivalent of the added tone known as the 6th, or when added to a symbol just the plain numberal "6" is used.
Each chord has a root. If the root is repeated, it is called the octave.
To locate the various 7ths follow this proceedure. Figure the note for the octave. Move 1 fret lower and that note is the major 7th interval. Move the note an additional fret lower and that note becomes the regular 7th. Move another additional fret and that note becomes the diminished 7th interval or the 6th.
The assumption here is that the viewer knows the distances between the notes on the fret board. See Lesson # ....
If you have a C chord, the C is the octave. One fret to the left is the note B. That is the major 7th interval and is written on a chord symbol as maj7. One more additional fret to the left gives us the note Bb. That is the minor 7th interval and is written as the plain numeral "7" on a chord symbol.One more additional fret to the left and that note is Bbb if one is thinking about a diminished 7th interval.. or if one thinks of that note as an A then it is a 6th and is written as plain numeral "6" on a chord symbol.
