219 lines
8.2 KiB
Python
219 lines
8.2 KiB
Python
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"""
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songkit — composition helpers built on midikit.
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The patterns that make MIDI sound like a 1993 sound card rather than a
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MIDI file: OPL-style 16th arpeggios, square-lead pitch-bend vibrato,
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driving 8th-note bass, velocity humanising, and bar-based song structure.
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All times are in bars.beats as floats: bar(t, beat=0) with 4/4 and your
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file's tpq. E.g. with tpq=480, bar(2.5) == start of beat 3 of bar 3.
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"""
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from midikit import Track, GM, DRUMS, note as N
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TPQ = 480 # ticks per quarter; songs should agree with this
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def bar(t, beat=0.0, tpq=TPQ):
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"""Absolute tick for bar t (0-based float), beat within bar (0..4)."""
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return int(round((t * 4 + beat) * tpq))
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def q(tpq=TPQ):
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return tpq
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def parse_score(text, tpq=TPQ):
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"""Whitespace-separated note grid -> list of (tick, pitch, dur, vel).
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Grammar per token: PITCH[-dur[-vel]]
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pitch: C0..C9 with #/b/suffixes (e.g. D4, A#5, Bb3)
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dur: 1=whole 2=half 4=quarter (default) 8=eighth 16=sixteenth
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vel: 1-127 (default 100)
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rests: r4 / r8 / r2 / r16 / r1
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Bars may be separated with '|'. If any '|' is present, every bar
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segment must total exactly 4 quarter notes — a free bar-length
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linter that has saved me from more off-by-one-eighth bugs than
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I care to admit.
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Example: 'D4 A4-8 D5-8 F5-8 E5-4 D5-2'
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"""
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out = []
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tick = 0
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bar_ticks = 0
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bar_no = 1
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for tok in text.split():
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if tok == "|":
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if bar_ticks != tpq * 4:
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raise ValueError("bar %d totals %d ticks, expected %d (4/4)"
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% (bar_no, bar_ticks, tpq * 4))
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bar_ticks = 0
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bar_no += 1
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continue
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if tok.startswith("r"):
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dur = {"r1": tpq * 4, "r2": tpq * 2, "r4": tpq, "r8": tpq // 2,
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"r16": tpq // 4}.get(tok, tpq // 4)
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tick += dur
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bar_ticks += dur
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continue
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parts = tok.split("-")
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pitch = N(parts[0])
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dur = tpq // 4
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vel = 100
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if len(parts) > 1 and parts[1]:
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dur = {"1": tpq * 4, "2": tpq * 2, "4": tpq, "8": tpq // 2,
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"16": tpq // 4}[parts[1]]
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if len(parts) > 2 and parts[2]:
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vel = int(parts[2])
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out.append((tick, pitch, dur, vel))
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tick += dur
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bar_ticks += dur
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return out
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def melody(track, start_bar, score, channel=0, tpq=TPQ):
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"""Lay a parse_score() grid onto a track starting at a bar."""
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base = bar(start_bar, tpq=tpq)
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for t, p, d, v in parse_score(score, tpq):
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track.note(base + t, p, d, v, channel)
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return track
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def chord(track, tick, root_name, quality, octave, velocity=80, duration=TPQ * 4, channel=0):
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"""Play a chord: chord(t, 'D', 'm', 3) -> D3 F3 A3."""
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root = N(root_name + str(octave))
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for iv in QUALITIES[quality]:
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track.note(tick, root + iv, duration, velocity, channel)
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return track
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QUALITIES = {
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"": (0, 4, 7), "maj": (0, 4, 7), "m": (0, 3, 7), "dim": (0, 3, 6),
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"aug": (0, 4, 8), "sus2": (0, 2, 7), "sus4": (0, 5, 7),
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"7": (0, 4, 7, 10), "maj7": (0, 4, 7, 11), "m7": (0, 3, 7, 10),
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"m7b5": (0, 3, 6, 10), "6": (0, 4, 7, 9), "m6": (0, 3, 7, 9),
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"9": (0, 4, 7, 10, 14), "add9": (0, 4, 7, 14), "sus": (0, 5, 7),
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}
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def arp(track, start_bar, chords, pattern="0121", subdivision=4, velocity=70,
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octave=4, duration=None, channel=0, tpq=TPQ, raise_bass_octave=True):
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"""OPL/Sound Blaster staple: 16th-note arpeggios following a chord chart.
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chords: list of (root, quality) per bar, e.g. [('D','m'), ('Bb',''), ...]
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pattern: indices into the chord tones (bass octave bump on index 0).
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subdivision: notes per beat (4 = sixteenths).
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"""
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per_bar = 4 * subdivision
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if isinstance(pattern, str):
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pattern = tuple(int(c) for c in pattern)
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for i, (root, qual) in enumerate(chords):
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tones = [N(root + str(octave)) + iv for iv in QUALITIES[qual]]
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for s in range(per_bar):
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idx = pattern[s % len(pattern)] % len(tones)
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pitch = tones[idx]
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if idx == 0 and raise_bass_octave:
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pitch = tones[0] - 12 if tones[0] - 12 >= 36 else tones[0]
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t = bar(start_bar + i, s / subdivision, tpq)
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track.note(t, pitch, duration or tpq // subdivision, velocity, channel)
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return track
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def bass_drive(track, start_bar, chords, subdivision=2, velocity=95,
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octave=2, approach=True, channel=0, tpq=TPQ):
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"""Driving bass: repeated roots per bar (DOS adventure / racing staple),
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optional chromatic approach note on the last subdivision."""
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per_bar = 4 * subdivision
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for i, (root, _qual) in enumerate(chords):
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rootn = N(root + str(octave))
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for s in range(per_bar):
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pitch = rootn
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if approach and s == per_bar - 1:
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pitch = rootn - 1 # chromatic approach from below
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t = bar(start_bar + i, s / subdivision, tpq)
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track.note(t, pitch, int(tpq / subdivision * 0.9), velocity, channel)
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return track
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def vibrato(track, start_tick, end_tick, channel=0, depth=0.6, rate=5.5,
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tpq=TPQ, tempo_bpm=120, bend_range=2):
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"""Pitch-bend vibrato for square leads — the difference between a beep
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and an OPL voice. One bend per cycle; always resets at end_tick."""
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import math
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sec_per_tick = 60.0 / tempo_bpm / tpq
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ticks_per_cycle = 1.0 / rate / sec_per_tick
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t = start_tick
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phase = 0.0
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while t < end_tick:
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val = math.sin(phase) * depth * 8191
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track.bend_to(t, val / 8191 * bend_range, channel, bend_range)
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t += max(1, int(ticks_per_cycle / 2))
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phase += math.pi
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track.bend_reset(end_tick, channel)
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return track
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def humanize(vel, seed=0, amount=8):
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"""Deterministic pseudo-random velocity jitter — machine-gun velocities
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are the #1 tell of amateur MIDI."""
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x = (seed * 2654435761) & 0xFFFFFFFF
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x ^= x >> 13
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jitter = ((x * 1103515245) >> 16) % (2 * amount + 1) - amount
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return max(1, min(127, vel + jitter))
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# ---------------------------------------------------------------------------
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# Drum patterns (channel 9). Each returns list of (beat_offset, drum, vel).
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# ---------------------------------------------------------------------------
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def pattern_fill(name):
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return PATTERNS[name]
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PATTERNS = {
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# beat offsets within one bar (0..4)
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"dos_roll": [ # the classic DOS game fill: snare 16ths, crash on 1
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(i * 0.25, "snare", 90 + (i % 2) * 10) for i in range(16)
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],
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"rock": [
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(0, "bass1", 110), (1.5, "bass1", 95), (2.5, "bass1", 100),
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(1, "snare", 110), (3, "snare", 115),
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(0, "closedhat", 80), (0.5, "closedhat", 70), (1, "closedhat", 80),
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(1.5, "closedhat", 70), (2, "closedhat", 80), (2.5, "closedhat", 70),
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(3, "closedhat", 80), (3.5, "closedhat", 70),
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],
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"drive": [ # 150bpm racing: four-on-floor, 8th hats, snare 2&4
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(0, "bass1", 115), (1, "bass1", 110), (2, "bass1", 115), (3, "bass1", 110),
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(1, "snare", 115), (3, "snare", 120),
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(0, "closedhat", 85), (0.5, "closedhat", 75), (1, "closedhat", 85),
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(1.5, "closedhat", 75), (2, "closedhat", 85), (2.5, "closedhat", 75),
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(3, "closedhat", 85), (3.5, "closedhat", 75),
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],
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"halftime": [ # ambient/N64: sparse kick + soft shaker
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(0, "bass1", 70), (2, "bass1", 55),
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(0.5, "shaker", 45), (1.5, "shaker", 40), (2.5, "shaker", 45), (3.5, "shaker", 40),
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],
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"break": [ # busy 16th tom/snare break
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(0, "hightom", 105), (0.25, "midtom", 100), (0.5, "lowtom", 105),
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(0.75, "snare", 100), (1, "midtom", 105), (1.25, "hightom", 100),
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(1.5, "snare", 110), (2, "crash", 110),
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],
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"shufflesnare": [
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(i * 0.5 + (0.16 if i % 2 else 0), "snare", 85 + (i % 3) * 8) for i in range(8)
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],
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}
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def drums(track, start_bar, bars, pattern, channel=9, tpq=TPQ, velocity_scale=1.0):
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"""Lay a named pattern across N bars."""
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for b in range(bars):
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for beat_off, drum, vel in PATTERNS[pattern]:
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vel = max(1, min(127, int(vel * velocity_scale)))
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track.note(bar(start_bar + b, beat_off, tpq), DRUMS[drum],
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tpq // 4, vel, channel)
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return track
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def crash(track, tick, vel=110, channel=9):
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track.note(tick, DRUMS["crash"], TPQ, vel, channel)
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return track
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