write-trap-album

name	write-trap-album
description	Generate trap / melodic trap tracks (dark minor, 808 bass, hat rolls, half-time feel). Uses CoupledHMMHarmonizer with chord-tone-contour harmony and manual MixingDesk/MasteringDesk. Bass808Sliding, TrapDrums, HiHatStutter generators. pop profile for triadic minor trap, funk profile (dom7+min7) when you want transition dominants. Static axis forms or through-composed multi-section forms.

Write Trap Album

Use this skill for melodic trap (Lil Baby, Roddy Ricch, Drake trap-soul), drill, and dark minor trap. Half-time feel. Uses CoupledHMMHarmonizer + chord-tone-contour harmony + manual MixingDesk/MasteringDesk, with dedicated trap generators (Bass808SlidingGenerator, TrapDrumsGenerator, HiHatStutterGenerator).

1. Profile choice: pop (triadic) vs funk (transitions)

Trap harmony is minimal, so the choice is about what color you want, not complexity:

Goal	Profile	Result
Static dark trap, clean minor triads (Cm–Ab–Eb–Bb)	pop	major triads intact, no 7th color
Melodic trap with transitions (secondary dominants G7/Bb7 + dark m7 sonority)	funk	m7 + dom7 retained, but major triads get absorbed into m7 (see pitfalls)

• pop = completion_bonus=0 → clean triads only.
• funk = {8:5, 7:4} → retains dom7 (type 8) and min7 (type 7).
• Trade-off (important): the funk min7 bonus captures spelled major triads into the m7 a fifth below, because a major triad's tones are a subset of that m7 (Ab [8,0,3] ⊂ Fm7 [5,8,0,3]). So with funk, expect a lush all-minor/m7 texture with dom7 tension chords, NOT major/minor contrast. For major/minor contrast, use pop (but you lose dom7 transitions). You cannot cleanly have both.

2. Chord-tone contour — static axis vs through-composed

Static axis (C minor i–♭VI–♭III–♭VII, the rap/trap axis), repeated:

KEY = Scale(root=0, mode=Mode.NATURAL_MINOR)
FORM = ["i","bVI","bIII","bVII"]                         # loop these 4 bars
ARP  = {"i":[0,3,7], "bVI":[8,0,3], "bIII":[3,7,10], "bVII":[10,2,5]}  # Cm / Ab / Eb / Bb
# config=harmonizer_profile("pop")

Through-composed (interesting transitions): write a longer FORM with no exact repeat — mix in secondary dominants (V7/V7iv) and a Neapolitan (bII) across contrasting sections. Use the funk profile so the dom7 transitions retain:

FORM = [
  # A: dark axis (0–15)
  "i","bVI","bIII","bVII", "i","bVI","bIII","bVII", "i","bVI","bIII","V7", "i","iv","V7iv","i",
  # T: chromatic transition (16–23)
  "iv","V7","i","bVI", "bII","V7","i","V7iv",
  # B: lift (24–35) / O: cadential outro (36–47) ...
]
ARP = {"i":[0,3,7,10], "bVI":[8,0,3], "bIII":[3,7,10], "bVII":[10,2,5],
       "iv":[5,8,0,3], "V7":[7,11,2,5], "V7iv":[10,2,5,8], "bII":[1,5,8]}
# config=harmonizer_profile("funk")

(See scripts/albums/trap/melodic_trap_180.py for the full 48-bar worked example.)

Only spell chord types funk can anchor: min7 / dom7 / major triad. Avoid maj7 and half-dim (ø) — funk's bonus set can't pin them and they collapse ambiguously.

3. Required imports + pipeline

import random, sys, warnings
from pathlib import Path
REPO = Path(__file__).resolve().parents[3]; sys.path.insert(0, str(REPO))
warnings.filterwarnings("ignore"); random.seed(41)

from melodica.harmonize.coupled_hmm import CoupledHMMHarmonizer
from melodica.harmonize import harmonizer_profile
from melodica.generators import GeneratorParams
from melodica.generators.bass_808_sliding import Bass808SlidingGenerator
from melodica.generators.trap_drums import TrapDrumsGenerator
from melodica.generators.hihat_stutter import HiHatStutterGenerator
from melodica.generators.piano_comp import PianoCompGenerator
from melodica.generators.solo_melody import SoloMelodyGenerator
from melodica.generators.ambient import AmbientPadGenerator
from melodica.shorts_mixing import MixingDesk
from melodica.shorts_mastering import MasteringDesk
from melodica.midi import export_multitrack_midi

def _mix(raw, bpm, gains, lufs=-14.0):
    desk = MixingDesk(niche_cfg={}); desk.track_gains.update(gains)
    mixed = desk.apply_mixing(raw, [], int(bpm))
    mastered, _cc = MasteringDesk(target_lufs=lufs).apply_mastering(mixed)  # tuple
    return mastered

4. GM programs

SYNTH_BASS=38 (808), DRUMS=0, SYNTH_PAD=88, EPIANO=4 (Rhodes, to make chords audible), LEAD_SYNTH=85, CLEAN_GUITAR=27.

5. Generators (verified kwargs)

bass808 = Bass808SlidingGenerator(
    GeneratorParams(density=0.40, key_range_low=24, key_range_high=40),
    pattern="trap_basic", slide_probability=0.50, octave_range=2,
).render(chords, key, dur)                        # 808 sub-bass with pitch slides
drums = TrapDrumsGenerator(
    GeneratorParams(density=0.40),
    variant="standard", hat_roll_density=0.60, kick_pattern="standard",
    open_hat_probability=0.20, groove_swing=0.50,
).render(chords, key, dur)                        # full trap beat (kick/snare/hats w/ rolls)
hats = HiHatStutterGenerator(
    GeneratorParams(density=0.25),
    pattern="trap_eighth", roll_density=0.40, open_hat_probability=0.15,
).render(chords, key, dur)                        # extra hat rolls (optional; TrapDrums already has hats)
comp = PianoCompGenerator(
    GeneratorParams(density=0.26, key_range_low=48, key_range_high=72),
    comp_style="pop", voicing_type="close", accent_pattern="syncopated", chord_density=0.45,
).render(chords, key, dur)                        # makes chord changes audible under 808+drums
pad = AmbientPadGenerator(
    GeneratorParams(density=0.08, key_range_low=36, key_range_high=60),
    voicing="spread", overlap=0.4,
).render(chords, key, dur)
lead = SoloMelodyGenerator(
    GeneratorParams(density=0.22, key_range_low=60, key_range_high=84),
    style="blues_lick", blues_notes=True, chromaticism=0.30, vibrato_depth=0.3,
).render(chords, key, dur)                        # autotune-style melodic hook

6. Subgenres

Subgenre	Key	BPM	Profile	Form	LUFS	Example
Melodic trap (static)	C minor	140	pop	i-♭VI-♭III-♭VII axis	-14	scripts/albums/trap/melodic_trap.py
Melodic trap (through-composed)	C minor	180	funk	48-bar 4-section, transitions	-14	scripts/albums/trap/melodic_trap_180.py
Drill	Cm / Fm	140–145	pop	minor axis, sliding 808	-14	—

BPM is the true tempo; trap is felt half-time (140 ≈ 70, 180 ≈ 90). Hat rolls get denser at higher BPM — lower hat_roll_density if it clutters.

7. Pitfalls

Issue	Fix
Major triads (Ab/Eb/Bb) turned into m7	That's funk's min7 bonus capturing them (Ab ⊂ Fm7). Use pop if you want major/minor contrast; accept all-minor if you want dom7 transitions.
Neapolitan ♭II (Db) disappeared	Same capture (Db [1,5,8] ⊂ Bbm7). Only spell chords funk can anchor (min7/dom7/maj triad); avoid maj7 & ø.
Hats too busy at high BPM	TrapDrumsGenerator already includes hats — skip HiHatStutterGenerator, or lower hat_roll_density / roll_density.
Chord changes inaudible	Add a PianoCompGenerator (Rhodes) comp track so harmony is heard under the 808+drums.
Track transposed	Contour base must be a multiple of 12.
MasteringDesk crash	Returns tuple (mastered, cc) — unpack.