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96 lines
4.2 KiB
Plaintext
96 lines
4.2 KiB
Plaintext
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If you start to transfer music from fake books to MMA you'll find
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chords which look like C/E, Dm/C or Am/C. These chords are called
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"slash chords".
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Unfortunately, the notation used by arrangers and composers who
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create fakebooks and lead sheets in not nearly as standardized as one
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might like. And, when it comes to slash chords, the standard is far
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from firm. So, what to do in MMA?
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Let's look at the different ways that slash chords are used, but
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first lets revisit the method used by MMA to create a chord. MMA has
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a set of tables which represent each type of chord in terms of MIDI
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note values. These note values are adjusted for the particular scale.
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For example, the "notes" for a Major chord are stored in the table as
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(0,4,7). If you specify a F Major chord the notes will be converted
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to (5,9,12), which corresponds to F,A,C. In addition, each chord has
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a list of notes for a corresponding scale. A Major chord will have
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the notes for a Major scale, etc. So, in the previous example, a
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scale list (5,7...16) representing the notes F,G,A,Bb,C,D,E is also
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created.
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So, on to the slash chords ... we'll show different types and what MMA
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does and doesn't do.
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The easiest case is the simple inversion. In this case the slash note
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will be a note in the chord. Examples include Am/C, A/C# and C/E.
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MMA handles these by:
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- Rotating the chord so that the slash note becomes the root. An
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Am/C chord (A,C,E) becomes C,E,A; the C/E chord (C,E,G) becomes E,G,C.
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- Rotating the associated scale. In the case of Am/C the scale
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A,B,C,D,E,F,G becomes C,D,E,F,G,A,B.
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This may OR MAY NOT effect the output, especially if you have enabled
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MODE=OPTIMAL which may do chord rotation on its own. In most cases the
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bass notes will be effected.
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The next case encountered is a slash note which is not in the chord,
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but is in the scale. Example of this include C/B and Am/F. A C Major
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chord does not have a B note in it (although a B Major 7th chord
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does), but the scale associated with the C Major chord C,D,E,F,G,A,B
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does. So, MMA leaves the chord alone and rotates the scale to
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B,C,D,E,F,G,A. Scale lists are used for bass and scale patterns.
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Since scale patterns are mostly circular, the effect on these
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patterns is negligible; however, for bass patterns the root note (1)
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will be changed from C to F ... which is probably what you want.
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However, note that the 5th is also changed from G to F which might
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NOT be what you want.
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Yet another slash notation is to have the slash note as neither a
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scale or chord note. For example, one might want a C chord with the
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dominant 7th played ONLY in the bass. The notation for this would be
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C/Bb. If you encounter this, just change the chord to C7 and you'll
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probably be as close as you're going to get. We've played with
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different methods of handling this and haven't come up with anything
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satisfactory. We considered the following (all of which ignore the
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chord notes):
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- Just adding the Bb note to the scale. But, that's quite dumb since
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in the case of C/Bb we'd end up with a scale Bb,C,D,E,F,G,A,B. Not
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only is this 1 note too long (all scales are 7 notes long!) it has a
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B and Bb in it.
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- Add the note and drop the extra note. In the above case this gives
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us Bb,C,D,E,F,G,A. Perfect! But, what if we have C/Eb? If I saw this
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in a chart I'd probably figure that we want a Cm chord with the Eb
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played only in the bass. But, really, it could be just about
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anything. And, if we followed the add and drop routine we'd have
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Eb,C,D,E,F,G,A,B, which leaves that nasty E.
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- Find a "close" note, substitute and rotate. Well, not a bad idea.
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In the case of C/Bb we could parse the scale and discover that B is
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only one MIDI value away from Bb. Okay, lets change the B to a Bb and
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rotate. Perfect ... but, the note A is only one value out too. So,
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maybe that's the one to modify. If we had the tables listed as note
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names instead of MIDI values this might be simpler. But, as it is ...
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well, it's just not going to be reliable.
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So, in this case MMA just reports a failure, but doesn't barf.
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In some charts (not so much new ones, but you never know) you'll see
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things like Cm/9 or even Cm/dim. One can only guess at the meanings
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... and MMA avoids guessing. So, in these cases it just reports an
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error.
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bvdp, December/04
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