"""Song form: intro, verse, chorus, bridge, final chorus, and ending. Run from the root of a source checkout: python docs/site/examples/03_song_form.py [output-directory] The score has no section objects. Sections are a plain Python table of start beats; each part is written by functions that take a section and return notes on the absolute timeline. Dynamics come from velocity and from which tracks play in each section. Writes score.json, song.wav, song.mid, stems/, report.json, and sections.json. """ from __future__ import annotations import json import sys from pathlib import Path from audio_as_code import Note, Pattern, Song, Tone, Track, export_midi, render out = Path(sys.argv[1] if len(sys.argv) > 1 else "output/docs-examples/03-song-form") BPM = 92 BAR = 4 # (name, bars, chords): one chord symbol per bar, spelled as root + voicing. CHORDS = { "Dm": ("D2", ["D3", "F3", "A3", "C4"]), "Bb": ("Bb1", ["D3", "F3", "Bb3", "D4"]), "F": ("F2", ["C3", "F3", "A3", "C4"]), "C": ("C2", ["C3", "E3", "G3", "C4"]), "Gm": ("G2", ["D3", "G3", "Bb3", "D4"]), "A": ("A1", ["C#3", "E3", "A3", "C#4"]), } FORM = [ ("intro", ["Dm", "Bb", "Dm", "Bb"]), ("verse", ["Dm", "Bb", "F", "C", "Dm", "Bb", "Gm", "A"]), ("chorus", ["F", "C", "Dm", "Bb", "F", "C", "Gm", "A"]), ("bridge", ["Gm", "Dm", "Gm", "A"]), ("chorus 2", ["F", "C", "Dm", "Bb", "F", "C", "Gm", "A"]), ("ending", ["Dm", "Dm"]), ] # Turn the form into absolute beat positions. sections = [] beat = 0 for name, bars in FORM: sections.append({"name": name, "start": beat, "bars": bars}) beat += len(bars) * BAR END = beat # 136 beats verse_motif = Pattern.sequence( ["A4", None, "A4", "G4", "F4", None, "E4", "D4"], step=0.5, gate=0.8, velocity=0.62 ) chorus_motif = Pattern.sequence( ["C5", None, "A4", "C5", "D5", None, "C5", "A4"], step=0.5, gate=0.8, velocity=0.78 ) def harmony(section: dict, velocity: float, length: float = 3.9) -> list[Note]: notes = [] for bar, symbol in enumerate(section["bars"]): at = section["start"] + bar * BAR notes += [ Note(pitch=p, start=at, duration=length, velocity=velocity) for p in CHORDS[symbol][1] ] return notes def bassline(section: dict, velocity: float, busy: bool) -> list[Note]: notes = [] for bar, symbol in enumerate(section["bars"]): root = CHORDS[symbol][0] steps = ( [root, None, root, None, root, root, None, None] if busy else [root, None, None, None] ) step = 0.5 if busy else 1 notes += Pattern.sequence(steps, step=step, gate=0.85, velocity=velocity).at( section["start"] + bar * BAR ) return notes def melody(section: dict, motif: Pattern) -> list[Note]: """Play the motif in odd bars; follow the chord root a sixth up in the even bars.""" notes = [] for bar, symbol in enumerate(section["bars"]): at = section["start"] + bar * BAR if bar % 2 == 0: notes += motif.at(at) else: answer = Pattern.sequence([CHORDS[symbol][1][-1], None], step=2, gate=0.9) notes += answer.transpose(12).at(at) return notes def drums(section: dict, fill: bool) -> list[Note]: """drum_machine selects the voice by pitch: 36 kick, 38 snare, 42 hat, 45 tom, 49 cymbal.""" groove = Pattern.sequence( [[36, 42], 42, [38, 42], 42, [36, 42], [36, 42], [38, 42], 42], step=0.5, gate=0.3, velocity=0.7, ) bars = len(section["bars"]) notes = list(groove.repeat(bars - 1 if fill else bars).at(section["start"])) if fill: tom_fill = Pattern.sequence( [45, 45, 38, 45, 38, 38, 38, 38], step=0.5, gate=0.3, velocity=0.8 ) notes += tom_fill.at(section["start"] + (bars - 1) * BAR) return notes by_name = {s["name"]: s for s in sections} intro, verse, chorus, bridge, chorus2, ending = (by_name[n] for n, _ in FORM) piano = harmony(intro, 0.45) + harmony(verse, 0.5) + harmony(chorus, 0.62) piano += harmony(bridge, 0.4) + harmony(chorus2, 0.68) piano += [Note(pitch=p, start=ending["start"], duration=7.5, velocity=0.5) for p in CHORDS["Dm"][1]] cello = harmony(bridge, 0.6, length=3.8)[::4] # just the lowest voice of each bridge chord bass = bassline(verse, 0.7, busy=False) + bassline(chorus, 0.8, busy=True) bass += bassline(chorus2, 0.85, busy=True) bass.append(Note(pitch="D2", start=ending["start"], duration=6, velocity=0.7)) lead = melody(verse, verse_motif) + melody(chorus, chorus_motif) + melody(chorus2, chorus_motif) lead.append(Note(pitch="D5", start=ending["start"], duration=6, velocity=0.6)) kit = drums(verse, fill=True) + drums(chorus, fill=True) + drums(chorus2, fill=False) kit.append(Note(pitch=49, start=ending["start"], duration=6, velocity=0.6)) song = Song( title="Song form", bpm=BPM, beats=END, seed=3, tracks=[ Track( name="Piano", instrument="piano", gain=0.38, pan=-0.2, tone=Tone(brightness=0.45), notes=tuple(piano), ), Track(name="Bridge cello", instrument="cello", gain=0.5, pan=-0.35, notes=tuple(cello)), Track(name="Bass", instrument="bass_guitar", gain=0.62, notes=tuple(bass)), Track(name="Flute lead", instrument="flute", gain=0.42, pan=0.25, notes=tuple(lead)), Track(name="Kit", instrument="drum_machine", gain=0.45, notes=tuple(kit)), ], ) song.save(out / "score.json") report = render(song, out / "song.wav", stems_dir=out / "stems") export_midi(song, out / "song.mid") (out / "report.json").write_text(json.dumps(report, indent=2) + "\n", encoding="utf-8") seconds_per_beat = 60 / BPM table = [ { "name": s["name"], "start_beat": s["start"], "end_beat": s["start"] + len(s["bars"]) * BAR, "start_seconds": round(s["start"] * seconds_per_beat, 2), } for s in sections ] (out / "sections.json").write_text(json.dumps(table, indent=2) + "\n", encoding="utf-8") for row in table: beats = f"{row['start_beat']:>3}-{row['end_beat']:<3}" print(f"{row['name']:>9} beats {beats} at {row['start_seconds']:6.2f} s") print(f"total {song.seconds:.1f} s, peak {report['wav']['peak']:.3f}") print("warnings:", report["warnings"] or "none")