Demo gallery

Six pieces made by GBK's own composition engine through the same tools ChatGPT uses: one create call with a fixed seed, then typed edits, then a server render. The notes, audio, and explanations all come straight from the engine's output, with nothing written or played by hand.

Baroque Fugue in D minor

Prompt: “Compose a 16-bar four-voice Baroque fugue in D minor for organ, then add a CC11 crescendo into the final entry.”

What's in it

16 bars of 4/4 at 76 BPM in D minor (50.5 s), 1258 notes on 4 tracks.
Sections: Introduction (bars 1–2), Theme (bars 3–8), Development (bars 9–14), Coda (bars 15–16).
Organ (accompaniment): 315 notes from E2 to D5, first entry in bar 1.
Organ (accompaniment): 317 notes from E2 to G5, first entry in bar 1.
Organ (accompaniment): 313 notes from E2 to G5, first entry in bar 1.
Organ (accompaniment): 313 notes from E2 to G5, first entry in bar 1.
All 4 pitched parts start together in bar 1.
Expression (CC11) has 268 points from bar 1 to bar 17, moving from 70 to 127 (a crescendo).

All four voices enter together in bar 1. This is not a textbook fugue exposition: GBK's engine does not yet stagger the subject and answer entries.

Tracks

Track	Role	Instrument	Notes	Controllers
Organ	accompaniment	Church Organ	315	CC11, CC91
Organ	accompaniment	Church Organ	317	CC11, CC91
Organ	accompaniment	Church Organ	313	CC11, CC91
Organ	accompaniment	Church Organ	313	CC11, CC91

Download WAV (9.0 MB) Download MIDI

Recipe and reproducibility

WAV: 44100 Hz, 2 ch, 16-bit, 53.5 s, sha256 34d810cca7816b1a2777f2c0769cd26fa4356bc7d036011e4d2070c39eeccfb5. MIDI: SMF format 1, 5 tracks, 480 PPQ, sha256 65720cb929c4b5ddfce23a3dc0983149cce2ce8dff3e15458639bfaa9042dce0. Seed 1720, revision 2, rendered by the server renderer (SoundFont: default) on compose.grepawk.com at commit d329875, 2026-10-25T03:19:16.150Z.

{
  "gbk_create_composition": {
    "title": "Baroque Fugue in D minor",
    "style": "baroque",
    "key": "D minor",
    "tempo": 76,
    "bars": 16,
    "voices": 4,
    "instrumentation": [
      "organ",
      "organ",
      "organ",
      "organ"
    ],
    "seed": 1720
  },
  "gbk_edit_composition": [
    [
      {
        "type": "cc_curve",
        "trackIds": "@all",
        "controller": 11,
        "startBar": 9,
        "endBar": 16,
        "shape": "crescendo",
        "from": 70,
        "to": 127
      }
    ]
  ]
}

Two-Part Invention in F major

Prompt: “Write a 12-bar two-part invention in F major for harpsichord: a melody in the right hand and imitative counterpoint in the left.”

What's in it

12 bars of 4/4 at 96 BPM in F major (30.0 s), 377 notes on 2 tracks.
Sections: Introduction (bars 1–2), Theme (bars 3–6), Development (bars 7–10), Coda (bars 11–12).
Harpsichord (accompaniment): 185 notes from F3 to G5, first entry in bar 1.
Harpsichord (accompaniment): 192 notes from G2 to A4, first entry in bar 1.
Both pitched parts start together in bar 1.
Expression (CC11) has 26 points from bar 1 to bar 13, moving from 70 to 79 (a crescendo).

Tracks

Track	Role	Instrument	Notes	Controllers
Harpsichord	accompaniment	Harpsichord	185	CC11, CC91
Harpsichord	accompaniment	Harpsichord	192	CC11, CC91

Download WAV (5.6 MB) Download MIDI

Recipe and reproducibility

WAV: 44100 Hz, 2 ch, 16-bit, 33.0 s, sha256 e6a4fe53376be9f05d13d71d6ad2ca6eb5482d0ba0723d6711280e5a690db194. MIDI: SMF format 1, 3 tracks, 480 PPQ, sha256 624f2c671fac6582c3f81f3e3b765ccbecc7302cfe9ecd563ecc7ac919f8d8ed. Seed 1723, revision 3, rendered by the server renderer (SoundFont: default) on compose.grepawk.com at commit d329875, 2026-10-25T03:19:31.526Z.

{
  "gbk_create_composition": {
    "title": "Two-Part Invention in F major",
    "style": "classical",
    "key": "F major",
    "tempo": 96,
    "bars": 12,
    "instrumentation": [
      "harpsichord",
      "harpsichord"
    ],
    "seed": 1723
  },
  "gbk_edit_composition": [
    [
      {
        "type": "generate_part",
        "track": "@0",
        "startBar": 1,
        "endBar": 12,
        "kind": "melody",
        "seed": 11
      },
      {
        "type": "generate_part",
        "track": "@1",
        "startBar": 1,
        "endBar": 12,
        "kind": "counterpoint",
        "againstTrack": "@0",
        "seed": 12
      }
    ]
  ]
}

Orchestral Cue in C minor

Prompt: “Compose a 24-bar orchestral cue in C minor for strings, woodwinds and brass that builds from quiet to a full climax, with a swell in the strings.”

What's in it

24 bars of 4/4 at 84 BPM in C minor (68.6 s), 861 notes on 7 tracks.
Sections: Intro (bars 1–8), Build (bars 9–16), Climax (bars 17–24).
Violin (melody): 171 notes from C4 to Eb6, first entry in bar 1.
Viola (harmony): 144 notes from G3 to F4, first entry in bar 1.
Cello (bass): 96 notes from C2 to Eb3, first entry in bar 1, 100% of them quarter notes.
Flute (melody): 82 notes from C4 to Bb4, first entry in bar 1, 85% of them quarter notes.
Clarinet (harmony): 144 notes from Bb3 to Ab4, first entry in bar 1.
Horn (harmony): 144 notes from G3 to F4, first entry in bar 1.
Trumpet (melody): 80 notes from G3 to F4, first entry in bar 1, 81% of them quarter notes.
All 7 pitched parts start together in bar 1.
Expression (CC11) has 608 points from bar 1 to bar 25, moving from 50 to 127 (a crescendo).

Tracks

Track	Role	Instrument	Notes	Controllers
Violin	melody	Violin	171	CC1, CC11, CC91
Viola	harmony	Viola	144	CC1, CC11, CC91
Cello	bass	Cello	96	CC1, CC11, CC91
Flute	melody	Flute	82	CC11, CC91
Clarinet	harmony	Clarinet	144	CC11, CC91
Horn	harmony	French Horn	144	CC11, CC91
Trumpet	melody	Trumpet	80	CC11, CC91

Download WAV (12.0 MB) Download MIDI

Recipe and reproducibility

WAV: 44100 Hz, 2 ch, 16-bit, 71.6 s, sha256 c70a8f2f183d2c576a2c361e15c93764c58cb8bc8afce24d8496c2def94bad18. MIDI: SMF format 1, 8 tracks, 480 PPQ, sha256 bfe4695f6a695c77e8bc8ecc1e77d50e5e69c292890cebca1e92b5e6a92094c6. Seed 2024, revision 4, rendered by the server renderer (SoundFont: default) on compose.grepawk.com at commit d329875, 2026-10-25T03:20:34.471Z.

{
  "gbk_create_composition": {
    "title": "Orchestral Cue in C minor",
    "style": "classical",
    "key": "C minor",
    "tempo": 84,
    "bars": 24,
    "instrumentation": [
      "violin",
      "viola",
      "cello",
      "flute",
      "clarinet",
      "horn",
      "trumpet"
    ],
    "seed": 2024,
    "sections": [
      {
        "name": "Intro",
        "startBar": 1,
        "bars": 8,
        "energy": 0.3
      },
      {
        "name": "Build",
        "startBar": 9,
        "bars": 8,
        "energy": 0.6
      },
      {
        "name": "Climax",
        "startBar": 17,
        "bars": 8,
        "energy": 1
      }
    ]
  },
  "gbk_edit_composition": [
    [
      {
        "type": "cc_curve",
        "trackIds": "@all",
        "controller": 11,
        "startBar": 1,
        "endBar": 24,
        "shape": "crescendo",
        "from": 50,
        "to": 127
      },
      {
        "type": "cc_curve",
        "track": "@0",
        "controller": 11,
        "startBar": 9,
        "endBar": 16,
        "shape": "swell",
        "from": 60,
        "peak": 120,
        "to": 90
      }
    ]
  ]
}

Game Soundtrack Loop in E minor

Prompt: “Make a loopable 16-bar game soundtrack in E minor at 132 BPM with a main theme (A) and a contrasting B section, drums and bass.”

What's in it

16 bars of 4/4 at 132 BPM in E minor (29.1 s), 467 notes on 4 tracks.
Sections: A (theme) (bars 1–8), B (contrast) (bars 9–16).
Piano (accompaniment): 128 notes from B3 to A4, first entry in bar 1.
Bass (bass): 64 notes from E1 to E2, first entry in bar 1, 100% of them quarter notes.
Strings (harmony): 96 notes from B3 to A4, first entry in bar 1.
Drums: 179 drum hits starting in bar 1.
All 3 pitched parts start together in bar 1.
Expression (CC11) has 163 points from bar 1 to bar 17, moving from 98 to 80 (a decrescendo).

The loop seam (bar 16 back to bar 1) has not been checked for smoothness.

Tracks

Track	Role	Instrument	Notes	Controllers
Piano	accompaniment	Acoustic Grand Piano	128	CC11, CC91
Bass	bass	Acoustic Bass	64	CC11, CC91
Strings	harmony	String Ensemble	96	CC1, CC11, CC91
Drums	percussion	Drum kit (ch 10)	179	CC91

Download WAV (5.4 MB) Download MIDI

Recipe and reproducibility

WAV: 44100 Hz, 2 ch, 16-bit, 32.1 s, sha256 cddb0b0d4c680f874e600991b4858cad53b1fec0455b24a8a5a240975dbd739c. MIDI: SMF format 1, 5 tracks, 480 PPQ, sha256 5e073235ce60121db80be1d82ab81726c65fd7602ca4042b1e1b437fbefc8112. Seed 3132, revision 2, rendered by the server renderer (SoundFont: default) on compose.grepawk.com at commit d329875, 2026-10-25T03:20:53.539Z.

{
  "gbk_create_composition": {
    "title": "Game Soundtrack Loop in E minor",
    "style": "pop",
    "key": "E minor",
    "tempo": 132,
    "bars": 16,
    "seed": 3132,
    "sections": [
      {
        "name": "A (theme)",
        "startBar": 1,
        "bars": 8,
        "energy": 0.8
      },
      {
        "name": "B (contrast)",
        "startBar": 9,
        "bars": 8,
        "energy": 0.5
      }
    ]
  },
  "gbk_edit_composition": []
}

Ambient Piano in A major

Prompt: “Compose a 16-bar ambient piano piece in A major at 64 BPM, then add a CC11 crescendo in bars 9–16.”

What's in it

16 bars of 4/4 at 64 BPM in A major (60.0 s), 96 notes on 1 track.
Sections: Introduction (bars 1–2), Theme (bars 3–8), Development (bars 9–14), Coda (bars 15–16).
Piano (accompaniment): 96 notes from Ab3 to F#4, first entry in bar 1.
Expression (CC11) has 70 points from bar 1 to bar 17, moving from 70 to 120 (a crescendo).

Tracks

Track	Role	Instrument	Notes	Controllers
Piano	accompaniment	Acoustic Grand Piano	96	CC11, CC91

Download WAV (10.6 MB) Download MIDI

Recipe and reproducibility

WAV: 44100 Hz, 2 ch, 16-bit, 63.0 s, sha256 8f9c8ec4345d4e76a106cb7f74b4b8eb174a4089a5609a0753b952eb833d396c. MIDI: SMF format 1, 2 tracks, 480 PPQ, sha256 cfa08ab90fb3aabfc79ba932699e793958caa9e3e3ba36be990faeb92ff12412. Seed 6464, revision 2, rendered by the server renderer (SoundFont: default) on compose.grepawk.com at commit d329875, 2026-10-25T03:21:02.862Z.

{
  "gbk_create_composition": {
    "title": "Ambient Piano in A major",
    "style": "ambient",
    "key": "A major",
    "tempo": 64,
    "bars": 16,
    "instrumentation": [
      "piano"
    ],
    "seed": 6464
  },
  "gbk_edit_composition": [
    [
      {
        "type": "cc_curve",
        "trackIds": "@all",
        "controller": 11,
        "startBar": 9,
        "endBar": 16,
        "shape": "crescendo",
        "from": 60,
        "to": 120
      }
    ]
  ]
}

Jazz in F major with Walking Bass

Prompt: “Write a 24-bar jazz piece in F major at 140 BPM with a walking bass, piano chords and drums, then add a CC11 crescendo in bars 17–24.”

What's in it

24 bars of 4/4 at 140 BPM in F major (41.1 s), 826 notes on 4 tracks.
Sections: Introduction (bars 1–4), Theme (bars 5–12), Development (bars 13–20), Coda (bars 21–24).
Trumpet (melody): 165 notes from D4 to Bb5, first entry in bar 1.
Piano (accompaniment): 192 notes from Bb3 to D5, first entry in bar 1.
Bass (bass): 192 notes from E1 to A2, first entry in bar 1, 100% of them quarter notes.
Drums: 277 drum hits starting in bar 1.
All 3 pitched parts start together in bar 1.
Expression (CC11) has 337 points from bar 1 to bar 25, moving from 70 to 127 (a crescendo).

Tracks

Track	Role	Instrument	Notes	Controllers
Trumpet	melody	Trumpet	165	CC11, CC91
Piano	accompaniment	Acoustic Grand Piano	192	CC11, CC91
Bass	bass	Acoustic Bass	192	CC11, CC91
Drums	percussion	Drum kit (ch 10)	277	CC91

Download WAV (7.4 MB) Download MIDI

Recipe and reproducibility

WAV: 44100 Hz, 2 ch, 16-bit, 44.1 s, sha256 bd060756e47c492aac029b6b8e23eeb52b1e4e0a441ffe591f844d1ade9c0b38. MIDI: SMF format 1, 5 tracks, 480 PPQ, sha256 b2ca500a4c232cf83874c5f5388ff1ddc7c20acb069aed24a52aa1413e81ef50. Seed 140, revision 3, rendered by the server renderer (SoundFont: default) on compose.grepawk.com at commit d329875, 2026-10-25T03:21:22.421Z.

{
  "gbk_create_composition": {
    "title": "Jazz in F major with Walking Bass",
    "style": "jazz",
    "key": "F major",
    "tempo": 140,
    "bars": 24,
    "seed": 140
  },
  "gbk_edit_composition": [
    [
      {
        "type": "generate_part",
        "track": "@role:bass",
        "startBar": 1,
        "endBar": 24,
        "kind": "walking_bass",
        "seed": 9
      },
      {
        "type": "cc_curve",
        "trackIds": "@all",
        "controller": 11,
        "startBar": 17,
        "endBar": 24,
        "shape": "crescendo",
        "from": 70,
        "to": 127
      }
    ]
  ]
}

Compose something like this with ChatGPT