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Transposition proposal: summary

4.6 Clefs and transposition

Additional text for section 4.6 Clefs and transposition

  • [shift-sound=<semitones>] - for playback, shift the sound in the current voice by the number of semitones indicated; positive numbers shift up, negative down. This setting does not affect the typeset score. The default is 0.
  • [shift-score=<semitones>[<enharmonic indicator>]] - for typesetting, shift the typeset score in the current voice by the number of semitones indicated; positive numbers shift up, negative down. This setting does not affect playback. The default is 0. The <enharmonic indicator> can optionally be used to clarify which key is meant - for more details see enharmonic indicators.
  • [shift-both=<semitones>] - for typesetting and playback, is equivalent to [shift-sound=<semitones>] used together with [shift-score=<semitones>].

The shift-sound parameter is equivalent to the transpose parameter of abc 2.1 and either may be used.

For more details of how the shift parameters may be used see enharmonic indicators, one-off transposition and writing abc code for transposing instruments.

4.6.1 Enharmonic indicators

Generally, when using shift-score, the key signature will be changed to the key signature which is closest in the cycle (helix) of fifths. However, if the key shifts through 6 or more steps in the cycle, it is no longer clear which key is required.

Example 1: The transposition K:C shift-score=10 indicates a change to K:Bb rather than K:A#, since Bb is only two steps away from C in the cycle of fifths (C - F - Bb), whereas A# is ten steps away (C - G - D - A - E - B - F# - C# - G# - D# - A#).

Example 2: The transposition K:C shift-score=6 is ambiguous as to whether K:Gb or K:F# is intended since both are six steps away from C in the cycle of fifths.

In ambiguous cases, enharmonic indicators b or # can be used (immediately after the number of semitones) to state which is required.

Example: The transposition K:C shift-score=6b would shift the typeset score to K:Gb whereas K:C shift-score=6# would shift it to K:F#.

By extension, enharmonic indicators bb or ## could be used when the key shifts through 13 or more steps in the cycle (although this is unlikely to ever occur in practice).

The following semitone shift table shows all the upward shifts (i.e. transposing up from the original key to the required key) between every key from K:Cb (seven flats) through to K:C# (seven sharps).

key required
original key Cb Gb Db Ab Eb Bb F C G D A E B F# C#
K:Cb 0 7 2 9 4 11 6# 1# 8# 3# 10# 5# 0# 7## 2##
K:Gb 5 0 7 2 9 4 11 6# 1# 8# 3# 10# 5# 0# 7##
K:Db 10 5 0 7 2 9 4 11 6# 1# 8# 3# 10# 5# 0#
K:Ab 3 10 5 0 7 2 9 4 11 6# 1# 8# 3# 10# 5#
K:Eb 8 3 10 5 0 7 2 9 4 11 6# 1# 8# 3# 10#
K:Bb 1 8 3 10 5 0 7 2 9 4 11 6# 1# 8# 3#
K:F 6b 1 8 3 10 5 0 7 2 9 4 11 6# 1# 8#
K:C 11b 6b 1 8 3 10 5 0 7 2 9 4 11 6# 1#
K:G 4b 11b 6b 1 8 3 10 5 0 7 2 9 4 11 6#
K:D 9b 4b 11b 6b 1 8 3 10 5 0 7 2 9 4 11
K:A 2b 9b 4b 11b 6b 1 8 3 10 5 0 7 2 9 4
K:E 7b 2b 9b 4b 11b 6b 1 8 3 10 5 0 7 2 9
K:B 0b 7b 2b 9b 4b 11b 6b 1 8 3 10 5 0 7 2
K:F# 5bb 0b 7b 2b 9b 4b 11b 6b 1 8 3 10 5 0 7
K:C# 10bb 5bb 0b 7b 2b 9b 4b 11b 6b 1 8 3 10 5 0

To calculate downward shifts, look up the number in the table and subtract 12 from it (leaving the enharmonic indicator unchanged).

Example: Transposing up from K:C to K:G (the row headed K:C and the column headed G) is a positive shift of 7 semitones and hence K:C shift-score=7 is used. Transposing down from K:C to K:G is (7 - 12) = -5 semitones.

Note that even though they are not specifically mentioned in the table, the semitone shifts also work for minor and modal keys, provided that both original and required key signatures are both minor or both in the same mode.

Example: Transposing up from K:Cmin to K:Gmin is a positive shift of 7 semitones (the same semitone shift as for K:C to K:G).

Finally note that enharmonic indicators can also be used for the shift-sound and shift-both parameters although they will only make a difference to the sound if the playback software can handle non-equal temperaments (since, for example, a Gb will sound exactly the same as an F# in equal temperament).

4.6.2 One-off transposition

In general, users may prefer to do a one-off transposition of a tune, from one key to another, using abc transposition software. Typically such software would read in the source abc file and then export the resulting transposed abc transcription to a separate file (or alternatively reads and display the source and transposed abc transcriptions via forms on web pages).

Recommendation to software developers: The abc standard does not prescribe how the transposition is to be specified and, for example, it can be done via sliders and/or text fields on a GUI or by command line parameters. Furthermore, the transposition change can be described by a change of key (e.g. C to G), an interval (e.g. up a fifth), a shift in semitones (e.g. up 7 semitones), or even the number of steps through the cycle of fifths (e.g. up one step). Choose the method(s) and description(s) that suit your users best.

However, it is also possible to specify one-off transpositions from within an abc file using the shift-both parameter which shifts both the sound output and the typeset score by a given number of semitones.

Examples:

K:C shift-both=2 % transpose up one tone from the key of C to the key of D
K:G shift-both=-5 % transpose down a fourth from the key of G to the key of D

The semitone shift table shows the number of semitones required to achieve any shift between every key from K:Cb (seven flats) through to K:C# (seven sharps).

4.6.3 Writing abc code for transposing instruments

Transposing instruments sound notes at a different pitch to which they are written. For example, a C written on a Bb clarinet score would be sounded as a Bb (and similarly a written D would be sounded as a C).

This section uses written pitch (i.e. the pitch that is written on a transposing instrument's score) and sounding pitch (i.e. the pitch is actually sounded) to distinguish between the two.

(Note: "sounding pitch" is also often referred to as "concert pitch"; however, confusingly, this term is also sometimes used to indicate "play A above middle C at 440Hz", so for in this section, the former terminology is preferred.)

When writing for transposing instruments, the abc music code can be transcribed either:

  • at written pitch, with a shift-sound indicator to change the sound output to sounding pitch
  • at sounding pitch, with a shift-score indicator to change the typeset score to written pitch

In either case, it is recommended that the abc code indicates which system is in use via a comment, although in general, shift-sound indicators would only ever be used for written pitch transcriptions and shift-score indicators would only be used for sounding pitch transcriptions.

Extended example: Suppose a Bb clarinet player and a violinist wish to play the same piece which simply consists of the notes CDEF in the key of C.

Since the violin is not a transposing instrument, the violinist's part is written (and sounded):

V:violin
K:C
CDEF|

For the clarinet part, there is a choice. If, for example, the clarinet player wants the abc music code to reflect what appears on the typeset score, the abc code can be transcribed at written pitch (i.e. the notes DEFG) with a shift-sound indicator:

V:Bb clarinet
K:D shift-sound=-2 % transcribed at written pitch, will be shifted to sound correctly
DEFG|

This will be rendered by abc playback software as the notes CDEF (i.e. shifted down two semitones) and by abc typesetting software as follows:

TODO: include typeset score image showing [K:D] DEFG

Alternatively, if, say, the composer of the piece prefers to work at sounding pitch, the clarinet part can be transcribed as sounded with a shift-score indicator to indicate that the typeset score is typeset at written pitch, two semitones up from where it is sounded:

V:Bb clarinet
K:C shift-score=2 % transcribed at sounding pitch, will be shifted to written pitch when typeset
CDEF|

This will also be rendered by abc playback software as the notes CDEF (i.e. shifted down two semitones) and by abc typesetting software as above.

Finally, if the I:shift none directive is used in the file header (or tune header), all the shift parameters in the file (or tune) will be ignored. This could, for example, be used to typeset a complete score at sounding pitch from an abc transcription containing shift-score parameters (which would otherwise shift their respective voices to written pitch).

abc/standard/v2.1/proposals/transposition/v1.txt · Last modified: 2012/01/05 13:41 by cwalshaw
 
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