Writing ABC for an AI singer: the exact format and common mistakes

If you already have a melody and chords, you can paste them into MuziAI and have the AI sing to them. But only one flavour of ABC is accepted: the two-voice form the singing model itself writes. Ask a general chat AI to "write ABC music" and you usually get something unreadable, because it writes everyday ABC. This post describes the real format, with numbers we measured on 58 scores the machine composed for our sample songs.

The eight header lines

The first eight lines are almost fixed. Only the BPM and the key change:

X:1
T:
M:4/4
L:1/16
Q:1/4=88
V: Vocal clef=treble name="Vocal Melody" snm="Vocal"
V: Ins clef=treble name="Ins Melody" snm="Inst."
K:C

All 58 scores use 4/4 and a 1/16 unit. The T: line stays empty because the title is typed in MuziAI's own field. The key must be a plain key (C, Am, F#, Bb), with no "major" or "minor" and no modes. Across the 58 scores, F is the most common key (21 songs), then Dm (11) and Eb (7).

Two voices and groups of bars

After the header the score is a series of groups. Each group has a V: Vocal line, one line of music, a V: Ins line and one line of music, and the two lines must hold the same number of bars (1 to 4). Section names go in a comment such as % verse or % chorus right before the first group of the section.

% verse
V: Vocal
"C"z2G2G2A2c2c2B4|"Am"A4G8z4|"F"z2A2A2B2c2d2c4|"G"B4G8z4|
V: Ins
Z4|

The Vocal voice carries the sung melody and every chord. The Ins voice is the instruments: in sung sections the machine leaves it empty (Z4 means four silent bars), while in the intro, interludes and outro it carries the lead line. Over the 58 scores the Ins voice has a median of only 77 notes in the whole song, because it speaks only where the singer is silent.

Every bar adds up to 16

With a 1/16 unit, each 4/4 bar must add up to exactly 16. The number after a note is its length in sixteenths, so G2 is an eighth note and A4 a quarter. The only lengths allowed are 1, 2, 3, 4, 6, 8, 12 and 16. For any other length, tie two notes of the same pitch with a dash: 10 is written c8-c2, 5 is c4-c.

Allowed chords

Chords are written in double quotes right before the note or rest where they begin. Root A to G (optionally # or b), plus one of: none, m, dim, aug, 7, maj7, m7, dim7, m7b5, sus4, sus2, 6, m6, 7sus4, m(maj7), and optionally a bass note after a slash (C/E). Familiar chords like C9, Cadd9, Cmaj or N.C. are not on the list; replace them with the nearest one.

Lyrics must run parallel to the score

The model pairs lyrics with the score in order. Over the 58 scores the median is about two bars per lyric line (2.0 to 2.25 in verses, choruses and bridges), and roughly 8 to 10 notes per verse line. So write lyrics split with [Verse], [Chorus] tags in the same order as the % comments in the score, one syllable per note. A chorus must be written out in full every time, never "x2".

Mistakes AIs keep making

• Putting a title in T:, changing to L:1/8 or Q:120, writing K:C major.
• Using repeat signs |: :|, double bars ||, slurs, grace notes, triplets or stacked chords like [CEG].
• Adding w: lyric lines under the notes, when the lyrics belong in MuziAI's lyrics box.
• Putting chords in the Ins voice, or leaving the two voices with different bar counts.
• No sections at all, or section tags in the lyrics in a different order from the comments in the score.

The quick way: use the skill

We packaged all the rules above into a skill you can load into Claude, ChatGPT or the AI you use. It makes the AI split the song properly, write lyrics and ABC that fit each other, then run a checking script before handing the result to you. That script is the very checker from the official skill pack of the singing model, so a score it reports as ACCEPTED is one MuziAI can read. Download the composing skill (.zip).

Limits and what we do not know

• The score fixes key, tempo, chords and structure fairly closely, but the melody is followed only loosely. We measured chord agreement (0.81 to 0.92 with a score, against 0.55 without one) but have not measured the sung melody.
• An ABC that passes the checker does not guarantee a good song: that depends on the melody you write.
• A chord-entry box in the style "Am F C G" was tried and left switched off, because the machine does not sing all the lyrics when the vocal line is nothing but rests.

Putting it to use

1. Compose lyrics with section tags and the score using the skill.
2. On the homepage, open the "Write your own lyrics" tab and paste the lyrics.
3. In the sheet music card press "Paste my ABC" and paste the code. The check says "Readable" or points to the line with the problem.
4. Pick "Melody and chords" to follow the score closely, or "Melody only" if you are changing genre.