Each line in the header corresponds to a field, and begins with a single uppercase letter and a colon (:), followed by the content of the field. The following shows an example of what a header may look like:

X: 3
T: Turkish March
C: W. Mozart
M: 2/4
L: 1/8
K: Am

According to this header, the title of the piece contained in this file is Turkish March, and was composed by a person named W. Mozart. The piece is in A minor (K: Am), and the default length of each note in the music is one eighth (L: 1/8). Each bar contains two quarter notes (M: 2/4).

The abc standard specifies a large number of fields. You are required to handle only the following subset:

• C: Name of the composer.
• K: Key, which determines the key signature for the piece.
• L: Default length or duration of a note.
• M: Meter. It determines the sum of the durations of all notes within a bar, expressed as a rational number like 4/4 or 3/8. The special meter C (“common time”) means 4/4, and C| (“cut common time”) means 2/2.
• Q: Tempo. It represents the number of beats of the given length to play per minute.
• T: Title of the piece.
• V: Voices used in the piece.
• X: Index number, similar to the track number in a recording. In this project, this field does not carry any meaning, as you are required to parse only one abc file at a time. However, the official standard designates this field to be mandatory in every abc file, and therefore, your parser must be able at least to read it (and may then discard it).

There are several additional requirements on the header:

• The first field in the header must be the index number (X).
• The second field in the header must be the title (T).
• The last field in the header must be the key (K).
• Each field in the header occurs on a separate line.

All fields other than X, T, and K are optional, and may appear in any order.

• When the field M is omitted, the default meter is 4/4.
• When the field L is omitted, a unit note length is set based on the meter. If the meter is less than 0.75, the default unit note length is a sixteenth note. If the meter is 0.75 or greater, it is an eighth note. For example, 2/4 = 0.5, so, the default unit note length is a sixteenth note, while for 4/4 = 1.0, or 6/8 = 0.75, or 3/4= 0.75, it is an eighth note. Notice that if neither M nor L fields are present, the default note length is an eighth.
• When the field Q is omitted, the default tempo is 100 beats per minute, where a beat is the default note length given by field L. Notice, however, that when Q is specified, it includes its own beat length, and the tempo is not necessarily based on L.
• When the field C is omitted, any reasonable string will suffice (e.g. Unknown).

A key signature is a set of sharps or flats associated with particular notes in the scale. A sharp causes every occurrence of that note to be played one semitone higher, and a flat causes every occurrence of that note to be played one semitone lower. For example, the key signature in the diagram shown on the right contains three sharps (placed on C, F, and G). Throughout the piece, every C, F or, G (irrespective of the octave) should be played one semitone higher. A key of either A major (denoted K:A) or F-sharp minor (denoted K:F#m) specifies these three sharps.

Your abc player should handle every major and minor key on this list of keys and their signatures. You should also note that the effect of the key signature can be temporarily overridden with an accidental, which appears immediately left of its target note. Accidentals are described in Accidentals.

The body of an abc file consists of a sequence of notes separated by bar lines. Middle C is denoted by

C

and the scale of C in this octave is represented by the sequence

CDEFGAB

The note C in the next higher octave is denoted by a lower case C

c

Therefore, the sequence of notes that represents the scale of C twice, going through two octaves, and starting with middle C is

CDEFGABcdefgab

Notes in the higher octave are denoted by appending an appropriate number of apostrophes (') immediately after their names. For example,

c'

represents C in the two octaves up from the middle C, and

c''

represents C in the three octaves up. Similarly, notes in the octaves below the middle C can be denoted by appending commas (,).

As a summarizing example, the following sequence of notes

may be represented by

C, D, E, F,|G, A, B, C|D E F G|A B c d|e f g a|b c' d' e'|f' g' a' b'|]

By default, every note has the length specified in the L header field (and when this field is absent, a length determined by the meter). The length of a particular note may be increased or decreased by appending a multiplicative factor to the note. For example, if the default note length is 1/8 (i.e. an eighth note), then the following sequence of notes

is represented by

A1/4 A/4 A/ A A2 A3 A4 A6 A8| A,1/4 A,/4 A,/ A, A,2 A,3 A,4 A,6 A,8 |]

Note that either the denominator or the numerator (or both) in a fractional multiplicative factor can be omitted. An absent numerator should be treated as 1, and an absent denominator as 2. In addition, any apostrophes or commas that indicate the deviation from the middle octave must precede the multiplicative factor.

The effect of the key signature as discussed in Header (K field) can be temporarily overridden using accidentals. An accidental can be a sharp (denoted by ^ in abc), a flat (_), or a natural (=). A sharp causes a note to be played one semitone higher, a flat one semitone lower, and a natural causes the note to be played as if the key were in C without any accidental. Double sharps (^^) and flats (__) are also allowed. An accidental only affects a single octave; for example, the accidental in the bar |^C D c C| would only affect the first and the last C notes of the bar.

The effect of an accidental on a note lasts through the remainder of the current bar, and can be overridden by another accidental that occurs in the same bar. The effect of the key signature is restored at the beginning of the next bar.

A rest is denoted by

z

and has the same default length as a note. Multiplicative factors have the same effect on rests as they do on notes, but accidentals cannot be applied to rests.

One or more notes may be played simultaneously in a chord. In abc, a chord is denoted by a group of notes between square brackets ([ and ]):

[CEG]

Notes within a chord may be embellished with an accidental or a multiplicative factor. If the notes in a chord have different durations, the duration of the chord is determined by the duration of the first note specified in the chord. For example, in [C2E4]G2, there would first be an E note and a C note playing together, and then an E note and a G note playing together.

A chord may not contain any rests or tuplets.

A tuplet is a consecutive group of notes that are to be played for a duration that is either greater or less than the sum of the individual notes within that group. In abc, a tuplet is denoted by an opening round bracket (, the tuplet number, and the actual notes in the tuplet. For example,

(3GAB

is a tuplet that consists of three notes, and called triplet.

In this project, we require you to handle ONLY duplets, triplets, and quadruplets. The duration of each type of the tuplets are as follows:

• Duplet: 2 notes in the time of 3 notes
• Triplet: 3 notes in the time of 2 notes
• Quadruplet: 4 notes in the time of 3 notes

For example, a triplet that contains three eighth notes is equal in duration to one quarter note; therefore, each eighth note in the triplet should be played 2/3 the duration of a standard eighth note.

A tuplet may not contain rests, but it may contain chords.

A tuplet may have notes and chords of different lengths. In the case of a triplet, you should play each note or chord for 2/3 of the original duration. For a duplet, 3/2 of the original durations. And for a quadruplet, 3/4 of the original durations.

A section of music that is enclosed within |: and :| is to be repeated once. For example, in the following fragment of abc,

|: C D E F | G A B c :|

the two bars are repeated, so the sequence of notes that your abc player should produce as output is:

C D E F G A B c C D E F G A B c

The begin repeat bar |: may be omitted; in this case, the repeat is from the beginning of a major section or the beginning of the musical piece.

A repeated section may have a different ending when it is played the second time. In abc, alternate endings are indicated using [1 and [2. For example,

|: C D E F |[1 G A B c | G A B B :|[2 F E D C |

should be played as

C D E F G A B c G A B B C D E F F E D C

Note that when the repeat is played the second time, the bar that begins with [1 is entirely skipped over. Also note that endings may span multiple bars and need not be the same length.

All of the abc constructs that we have discussed so far allow us to play only a single melodic line. Many pieces of music (e.g. orchestral or band music), however, involve multiple voices that are played simultaneously. Multiple voices do not belong to the official abc language definition, but have nevertheless become a part of the de facto standard among abc users.

Your abc player should be able to parse and play multiple voices as defined below. Your abc player is NOT required to be able to play different instruments or have varied timbres.

Voices are listed in the header of an abc file using one or more field lines that begin with V. The content of each voice field is the identifier for a particular voice, and can be an arbitrary string. For example, the header

X:0
T: Prelude No. 1
C: J. S. Bach
M:4/4
L:1/16
Q:1/4=100
V: upper
V: middle
V: lower
K:C

says that this piece of music contains three different voices, labeled upper, middle, and lower. There is no limit on the number of voices in a piece.

A V field line may re-appear in the middle of the body to indicate that the following sequence of notes belongs to a particular voice, until another voice field with a different identifier appears. For increased readability, middle-of-body voice fields are often placed between small sequences of bars for different voices in alternating fashion (as it is normally done in sheet music):

V: upper
z2 Gc eGce z2 Gc eGce | z2 Ad fAdf z2 Ad fAdf | 
V: middle
z E7 z E7 | z D7 z D7 |
V: lower
C8 C8 | C8 C8 |
V: upper
z2 Gd fGdf z2 Gd fGdf | z2 Ae aAea z2 Ae aAea |]
V: middle
z D7 z D7 | z E7 z E7 |]
V: lower
B,8 B,8 | C8 C8 |]

However, your abc player should not make any assumptions about the order or frequency of middle-of-body voice fields. For example, instead of interleaving voices as in the previous example, an abc author could write each voice in its entirety under a single middle-of-body voice field:

V: upper
z2 Gc eGce z2 Gc eGce | z2 Ad fAdf z2 Ad fAdf | z2 Gd fGdf z2 Gd fGdf | z2 Ae aAea z2 Ae aAea |]
V: middle
z E7 z E7 | z D7 z D7 | z D7 z D7 | z E7 z E7 |]
V: lower
C8 C8 | C8 C8 | B,8 B,8 | C8 C8 |]

The names or labels of the voices might indicate different instruments, for example. However, they have no significance for your music player because you do not need to play different instruments or have varied timbres. Your music player only needs to produce one kind of sound, and voices simply allow your player to play multiple melodic lines simultaneously.

Lyrics must follow immediately after the line of notes to which they are attached, and the lyrics must be written on a single line. Lyrics are not mandatory for all lines of notes in an ABC file.

Lyrics must be preceded by the w information field.

If there are fewer syllables than available notes, the remaining notes have no lyric (blank syllables).

If there are more syllables than available notes, any excess syllables will be ignored.

Each line of lyrics is broken up into syllables. Within the lyrics, the words should be separated by one or more spaces and to correctly align them the following symbols may be used:

-

(hyphen) break between syllables within a word

_

(underscore) previous syllable is to be held for an extra note

*

one note is skipped (i.e. * is equivalent to a blank syllable)

~

combines multiple words under one note; appears as a space when lyrics are printed;

\-

combines multiple syllables under one note; appears as a hyphen when lyrics are printed; note that this is a two-character sequence, backslash then hyphen

|

advances to the next bar

Note that if - is preceded by a space or another hyphen, the - is regarded as a separate syllable.

When an underscore is used next to a hyphen, the hyphen must always come first.

If there are not as many syllables as notes in a bar, typing a | automatically advances to the next bar; if there are enough syllables the | is just ignored.

Examples:

w: syll-a-ble    has 3 syllables aligned with 3 notes
w: syll-a-_ble   has 3 syllables aligned with 4 notes ("a" is held for 2 notes)
w: syll-a--ble   has 4 syllables aligned with 4 notes (an empty syllable between the double hyphen)
w: syll-a -ble   (equivalent to the previous line)
w: time__        has 1 syllable held for three notes
w: of~the~day    has 1 syllable aligned with 1 note, and appears as "of the day" when printed

gf|e2dc B2A2|B2G2 E2D2|G2G2 GABc|d4 B2
w: Sa-ys my au-l' wan to your aul' wan, Will~ye come to the Wa-x-ies dar-gle?

If a line of notes has lyrics, the lyrics will be written as a single line.

If a bar is repeated, you should also repeat its associated lyrics.

An abc file may contain comments, which start with % and continue until the end of the line.