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Transposition proposal - summary

This page contains the twelfth draft of a proposal to extend the transcription capabilities within abc. It involves only minor changes from the eleventh draft:

  • K: and V: modifiers now combine with other modifiers in the same field (although fields still override previous fields)
  • As a result the + parameter introduced in the eleventh draft for combining shift* changes is superfluous and has been removed
  • instrument=<note>;abc=concert is now a synonym for shift-score=<note>c shift-sound=cc and instrument=<note>;abc=written is a synonym for shift-sound=c<note> shift-score=cc - this means that when the instrument modifier overrides, it overrides both shift-score and shift-sound

The important aspects of this proposal are the same as versions 10 & 11:

  • A single system for transposition (rather than the dual high/low-level systems proposed previously) consisting of the well-establised shift-score and shift-sound operators which allow the typeset score and playback to be modified independently
  • transposition by interval (e.g. C to G), rather than by semitones as previously
  • instrument synonyms for shift-score and shift-sound, to give an intuitive specification for transposing instruments
  • shift shorthand for combined score and sound transpositions

I have included some notes and comments at the end.


4.6 Clefs and key/voice parameters

Additional text for section 4.6 Clefs and transposition

This section discusses support within abc for clefs and other features which affect the placement of the notes relative to the staff. It briefly mentions transposition, because the relevant syntax appears in the K:key and V:voice fields, but this topic is discussed in full in section 13, Transposition.

Clef, transposing instrument and related indications appear as modifiers to the K:key and V:voice fields; the possible modifiers are:

[clef=]<clef name>[<line number>][+8|-8] stafflines=<lines> octave=<number>
  shift-score=<note1><note2> shift-sound=<note1><note2>
  shift=<note1><note2> instrument=<note>;[abc=]concert|written

(where <…> denotes a value, […] denotes an optional parameter, and | separates alternative values).

Within a given voice, the modifiers of each K: or V: field are inherited from the previous K: or V: field, unless overriden - see scope and inheritance of modifiers for more details.

… unchanged …

  • shift-score=<note1><note2> transposes the typeset score according to the specified interval (the playback is not affected) - for more information see transposition operators;
  • shift-sound=<note1><note2> transposes the playback according to the specified interval (the typeset score is not affected) - for more information see transposition operators;
  • shift=<note1><note2> is a shorthand for shift-score=<note1><note2> shift-sound=<note1><note2> - for more information see transposition operators;
  • instrument=<note>;abc=concert is a synonym for shift-score=<note>c shift-sound=cc - for more information see writing abc code for transposing instruments;
  • instrument=<note>;abc=written is a synonym for shift-sound=c<note> shift-score=cc - for more information see writing abc code for transposing instruments;

… unchanged …

Note:

  • The transpose=<semitones> modifier of abc 2.1 and earlier is now deprecated (replaced by the shift-sound modifier - see transposition).
  • The middle=<pitch> modifier of abc 2.0 and earlier has been compromised in terms of what it was supposed to do and how it has actually been implemented. It is therefore deprecated.

TODO: Update deprecated list.

… unchanged …

4.6.1 Scope and inheritance of modifiers

As a fundamental rule, within each voice, each successive V: or K: field inherits the modifiers of the previous V: or K: field, unless it specifically overrides them.

Note: in other words, within a voice V: inherits from a K: field as well as from another V: field (and vice-versa).

Recommendation: In single-voice tunes these modifiers will normally be applied to the K: field. In multi-voice tunes it is recommended that they are only applied to V: fields (an additional V: field can even be introduced if one of the modifiers needs to change at a K: change). If a single-voice tune contains V: fields (for example, if it is a part extracted from a multi-voice score), then it is recommended that modifiers are applied to the V: fields.

Within each K: or V: field, modifiers may be arranged in any order and their effect is combined. In the specific case of shift-score or shift-sound modifiers mixed together with shift or instrument modifiers, replace the latter with their shift-score and shift-sound equivalents. For example, shift=CG shift-score=GF becomes shift-score=CG shift-sound=CG shift-score=GF and so the second shift-score combines with the first to give shift-sound=CG shift-score=CF.

However, modifiers written in each successive K: or V: field override modifiers inherited from previous fields. For example, [V:1 shift=CG][V:1 shift-score=GF] represent two different fields and so modifiers of the first are overridden by modifiers of the second. To evaluate their effects, first expand the shift in the first field to give [V:1 shift-score=CG shift-sound=CG][V:1 shift-score=GF]. The second field then inherits both modifiers but specifically overrides the shift-score to result in [V:1 shift-sound=CG shift-score=GF].

Finally note that there are two ways to specify octave shifts and, for example, octave=1 is equivalent to shift=Cc. However these operators can be used independently and so neither overrides the other.

13 Transposition

13.1 Transposition operators

The fundamental transposition operators are shift-sound and shift-score which act as modifiers for K:key and V:voice fields:

  • shift-score=<note1><note2> transposes the typeset score according to the specified interval (the playback is not affected)
  • shift-sound=<note1><note2> transposes the playback according to the specified interval (the typeset score is not affected)

Transpositions are applied to notes, grace notes, chords and key signatures.

The transposition interval is specified by two notes, <note1><note2>. Here <note1> refers to the transcribed abc code and <note2> refers to the rendered output (i.e. the typeset score in the case of shift-score or the playback in the case of shift-sound).

Example: In the following the typeset score is raised by a fifth and is rendered the same as if the abc code was transcribed as [K:D] efga. The playback is lowered by a tone and is rendered the same as if the abc code were [K:F] GABc.

K:G shift-score=CG shift-sound=DC
ABcd

Note: The interval system is clear with regard to enharmonics so, for example, the interval C to _G is distinct from C to ^F. However, to compute transpositions it may be helpful to use the MusicXML concept of specifying the interval as a combination of diatonic steps and semitones. Both of these can be easily calculated and make it simple to work out what the resulting note is using the diatonic steps to give the letter and the semitones to indicate whether it is flat, natural or sharp.

Examples: C to ^F is 6 semitones in 3 diatonic steps - C to D, D to E, E to F (as opposed to C to _G which is 6 semitones in 4 diatonic steps). Using this interval:

  • Eb (_E in abc code) transposes to A since A is 3 steps (letters) above E (in the cycle ABCDEFG) and the A is natural, since that note is 6 semitones above Eb
  • G transposes to C# (^c in abc code) since C is 3 steps above G and C# is 6 semitones above G
  • C# transposes to F## (^^F in abc code) since F is 3 steps above C and F## is 6 semitones above C#

Notes for developers: You should correct any transposition which goes beyond the specified abc limits to available key signatures, K:Cb (7 flats) to K:C# (7 sharps), and double/triple accidentals. For example, in principle K:C# shift-score=CG raises the key up to K:G# (8 sharps), so to keep with the limits it should be rendered as K:Ab (4 flats).

TODO (elsewhere in the standard): Limit the range of key signatures supported by abc to K:Cb (7 flats) through to K:C# (7 sharps). (Also limit accidentals - e.g. double sharp and double flat accidentals should be supported, but triples are entirely optional.)

To specify the same transposition for both score and sound, just use shift=<note1><note2> as a shorthand.

Example: The following two K:key fields are equivalent

K:G shift-score=CG shift-sound=CG
K:G shift=CG

13.2 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 concert pitch (i.e. the pitch that is actually sounded) to distinguish between the two.

Note: The term "concert pitch" is also used elsewhere in the musical lexicon to indicate "play A (above middle C) at 440Hz". However, here it refers to the pitches that transposing instruments actually sound.

There are two ways of writing abc code for transposing instruments:

  1. The abc code can be transcribed at concert pitch with shift-score=<note1><note2> modifiers used to transpose the typeset scores appropriately. If preferred the instrument=<note>;abc=concert modifier can be used as a synonym for shift-score=<note>c shift-sound=cc. Here the abc= is optional so this could be written instrument=<note>;concert.
  2. The abc code can be transcribed at written pitch with shift-sound=<note1><note2> modifiers used to transpose the playback appropriately. If preferred the instrument=<note>;abc=written modifier can be used as a alternative for shift-sound=c<note> shift-score=cc. Again the abc= is optional so this could be written instrument=<note>;written.

In both cases the typeset score is rendered at written pitch by default.

If a concert pitch score is required the I:concert-score instruction can be applied, either in the file header or the tune header. For transcriptions at concert pitch this has the effect of cancelling all of the shift-score modifiers (and the instrument=<note>;abc=concert alternative). For transcriptions at written pitch it has the effect of altering shift-sound modifiers (and the instrument=<note>;abc=written alternative) to shift modifiers.

Note 1: The <note> in the instrument=<note> syntax is a note and not a key (so that different octaves may be specified and so that the letter b is not ambiguous). Therefore, for a Bb instrument you must write instrument=_B and not instrument=Bb.

Note 2: The rationale for including shift-sound=cc (which is in effect a transposition from a note to itself) as part of the synonym for instrument=<note>;abc=concert and shift-score=cc as part of instrument=<note>;abc=written is to completely cancel the previous transposing instrument setting, so that everything works when a voice switches from abc encoded at written pitch to abc encoded at concert pitch, or vice-versa.

The following example illustrates the principles of writing for transposing instruments.

13.2.1 Transposing instruments - 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:1 name=violin
K:C
CDEF|

For the clarinet part, there is a choice. If, say, the composer of the piece prefers to work at concert pitch, the clarinet part can be transcribed as sounded, either using shift-score:

V:2 name=clarinet shift-score=_Bc
K:C
CDEF|

or using instrument as a alternative:

V:2 name=clarinet instrument=_B;abc=concert
K:C
CDEF|

This will be rendered by abc typesetting software according to the shift (i.e. [K:D] DEFG) but sounded as transcribed (i.e. CDEF). If a concert pitch score is required it can be typeset by adding an I:concert-score instruction.

Alternatively, if the composer wants the abc code at written pitch, the same piece can be transcribed:

V:2 name=clarinet shift-sound=c_B
K:D
DEFG|

or using instrument as a alternative:

V:2 name=clarinet instrument=_B;abc=written
K:D
DEFG|

This will be rendered by abc typesetting software as transcribed (DEFG) but sounded according to the shift (i.e. CDEF). Again, if a concert pitch score is required it can be typeset by adding an I:concert-score instruction.

Note: Written pitch voices will almost always need their own K: field to set the key correctly (which will be different from concert pitch voices).

The whole piece could then be transcribed at concert pitch as:

K:C
V:1 name=violin
CDEF|
V:2 name=clarinet instrument=_B;abc=concert
CDEF|

or at written pitch as:

K:C
V:1 name=violin
CDEF|
V:2 name=clarinet instrument=_B;abc=written
K:D
DEFG|

In either case the typeset score will be rendered at written pitch (and the playback at concert pitch). To obtain a concert pitch score, add an I:concert-pitch instruction in the file or tune header.

Re-transposition: Finally, suppose that the clarinet player has fallen ill and is to be replaced by an alto sax player who now needs a transposed part to read. If the abc code has been transcribed at concert pitch this is extremely easy by replacing instrument=_B;abc=concert with instrument=_E;abc=concert in the clarinet part:

V:2 name="alto sax" instrument=_E;abc=concert
CDEF|

If the abc code has been transposed at written pitch (in this case for a Bb instrument), it is a little harder.

The instrument=_B;abc=written can remain, as it is adjusting the playback to concert and also will serve as a reminder that the part was originally transcribed at written pitch for a Bb instrument.

To adjust the score, consider that the Bb clarinet score is written a major second higher than it is sounded (so C is written D) whereas the alto sax is written a major sixth higher than it is sounded (so C is written A). Since the abc code is already transcribed a tone higher, it needs to be raised by a further fifth (i.e. a major sixth less a major second) and so one way to do it is to use shift-score=CG (or shift-score=DA if that is easier to think about). The resulting code is:

V:2 name="alto sax" instrument=_B;abc=written shift-score=CG
K:D
DEFG|

This can be thought of as a reminder that the part is encoded at written pitch for a Bb instrument but the score is additionally transposed a fifth higher (i.e. for an instrument a fifth lower).

Another way to express this is to use the fact that a second V: field overrides parts of the first. In this following excerpt, the first V: field shows details of the original transcription for clarinet, whilst the second shows the re-transposition adjustments for alto sax:

V:2 name=clarinet instrument=_B;abc=written
V:2 name="alto sax" shift-score=CG
K:D
DEFG|

Depending on how you think about re-transposition, a further way to do this is to write:

V:2 name="alto sax" instrument=_E;abc=written shift=CG
K:D
DEFG|

This can be thought of as a reminder that the score is at written pitch for an Eb instrument but that the abc is encoded for an instrument a fifth higher.

Once again overriding can be brought into play - however, both new modifiers (instrument and shift) are required for the re-transposition to work and so in fact the second V: field completely overrides everything in the first:

V:2 name=clarinet instrument=_B;abc=written
V:2 name="alto sax" instrument=_E;abc=written shift=CG
K:D
DEFG|

One final way to do this, if you consider that the instrument modifier is ambiguous (the abc is encoded for a Bb instrument but the score will be typset for an Eb instrument) is just to use shift-score and shift-sound modifiers:

V:2 name="alto sax" shift-score=CG shift-sound=c_B
K:D
DEFG|

However, these examples suggest that, all other things being equal, it is rather more flexible to transcribe the abc code at concert pitch rather than at written pitch.

Finally note that all of the transposing instrument information would normally be collected up in the tune header to make it more visible (it only needs to appear in the body if something changes halfway through, such as a switch from Bb clarinet to A clarinet). So the written pitch clarinet to alto sax re-transposition excerpt could be transcribed as:

T:Duet for violin and clarinet (actually played on an alto sax)
V:1 name=violin
V:2 name=clarinet instrument=_B;abc=written
V:2 name="alto sax" shift-score=CG
K:C
V:1
CDEF|
V:2
K:D
DEFG|

13.2.1 Transposing instrument examples

The following table lists some example transposing instruments and the modifiers they would need

abc at concert pitch abc at written pitch
Instrument shift-score shift-sound instrument
piccolo shift-score=c'c shift-sound=cc' instrument=c'
Bb clarinet shift-score=_Bc shift-sound=c_B instrument=_B
soprano sax shift-score=_Bc shift-sound=c_B instrument=_B
A clarinet shift-score=Ac shift-sound=cA instrument=A
alto flute shift-score=Gc shift-sound=cG instrument=G
cor anglais shift-score=Fc shift-sound=cF instrument=F
alto sax shift-score=_Ec shift-sound=c_E instrument=_E
tenor sax shift-score=_B,c shift-sound=c_B, instrument=_B,

13.3 Transposing a file

To transpose an entire file, use the instruction I:shift-score <note1><note2>, I:shift-sound <note1><note2> or, as a shorthand for both, I:shift <note1><note2>. When placed in the file (or tune) header they have the the effect of adding the corresponding shift-score=, shift-sound= or shift= modifiers to every K: and V: field in the file (tune) which will then be combined with existing modifiers.

Example: The following excerpts are equivalent; in the former the I:shift-score cC (downwards octave transposition) is applied to the K: field and combines with the existing shift-score modifier to give the latter.

I:shift-score cC
K:C shift-score=_Bc
CCCC|
K:C shift-score=_BC
CCCC|

Notes and comments on the proposal

I welcome comments on all of the above proposal but in particular:

  • After suggestions on the tenth proposal I made the transposing instrument modifiers much more explicit - i.e. instrument=<note>;abc=concert and instrument=<note>;abc=written. A number of other suggestions have been made for the qualifier which specifies whether the abc is encoded at concert or written pitch including the following (I don't really mind which we end up with):
    • concert-encoded / written-encoded - a little more verbose
    • concert / written - perhaps a little too terse and open to being misinterpreted by a user as relating to the typeset score (although this proposal does allow for these as shorthand)
    • abcAsSound / abcAsScore - personally I don't find these very intuitive (particularly because it means that instrument=<note>;abcAsScore is an alternative for shift-sound=c<note> and vice-versa, and also because abcAsScore really means abcAsWrittenScore, since the score can either be typeset at concert or written pitch)
  • With the combining modifiers in this proposal, we could now define octave as a synonym for shift (e.g. octave=1 is equivalent to shift=Cc) and thus reduce the number of independent modifiers.
  • One mechanism missing from the proposal is allowing provision for clefs which change between a concert pitch score its written pitch counterpart. However, since transposing instruments are always typeset at written pitch (except when I:concert-score is present), that means we just need something like concert-clef=treble (which would only apply when I:concert-score is present) to handle this.

A recurring question is whether independent shift-score and shift-sound modifiers are actually necessary. I have discussed this separately in the independent-shift use-case.

Chris Walshaw, June 2014

abc/standard/v2.1/proposals/transposition/v12.txt · Last modified: 2014/06/24 04:21 by cwalshaw
 
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