music-theory

Music theory for Strudel

Scale choice by mood

Set the mode first; it does more for mood than any effect.

Scale	Mood	Strudel
minor (aeolian)	dark, serious	.scale("A:minor")
dorian	dark but cool, groovy (minor with a bright 6th)	.scale("D:dorian")
phrygian	tense, menacing (b2 against the root)	.scale("E:phrygian")
lydian	dreamy, floating (#4)	.scale("F:lydian")
mixolydian	warm, bluesy major (b7)	.scale("G:mixolydian")
major	bright, plain	.scale("C:major")
minor pentatonic	safe melodic minor palette — no wrong notes	.scale("A:minor:pentatonic")
major pentatonic	safe sunny palette	.scale("C:major:pentatonic")
harmonic minor	dramatic, exotic	.scale("A:harmonic:minor")

n() values are zero-based scale degrees with .scale() (degree 0 = root, 7 = root an octave up; negatives go below). The root may carry an octave: "A2:minor".

n("0 2 4 7").scale("D:dorian")
n("0 .. 7").scale("E:phrygian").s("sawtooth")

Progressions: two renderings

As chord symbols — chord() + voicing()

voicing() turns symbols into concrete notes with smooth voice leading between successive chords — this is your voice-leading engine; prefer it over hand-stacked chords for progressions.

// minor i–VI–III–VII (epic/pop-dark), in A minor
chord("<Am F C G>").voicing().s("piano")

// jazz ii–V–I with 7ths, in C
chord("<Dm7 G7 C^7 C^7>").voicing().s("piano").room(.3)

// major I–V–vi–IV (the big-pop loop), in F
chord("<F C Dm Bb>").voicing().s("sawtooth").attack(.1).gain(.45)

// dorian two-chord vamp (i7–IV7), in D
chord("<Dm7 G7>").voicing().struct("x ~ x ~ ~ x ~ ~")

Stick to common symbol forms: m, 7, m7, ^7 (maj7), 9, m9, sus4, b13. Steer the register with .anchor("e4").mode("below"); arpeggiate a voicing with .n("0 1 2 3") or .arp("0 2 1 3").

As scale degrees — n().add(n(...)).scale()

Move a chord shape diatonically by adding degrees — terse and always in key. The add must be keyed (n(...)) and come before .scale(); a plain .add("<...>") on a control pattern silently does nothing:

// triads on degrees 0, 5, 3, 4 of A minor (i–VI–iv–v)
n("[0,2,4]").add(n("<0 5 3 4>")).scale("A:minor").s("sawtooth").gain(.4)

Bass follows the roots

rootNotes(octave) extracts each chord's root — the reliable way to keep bass and harmony locked. Share one progression const between voices.

setcpm(96/4)
const prog = chord("<Am7 F^7 C^7 G7>");
$: prog.voicing().s("piano").gain(.6).room(.3)
$: prog.rootNotes(2).s("sawtooth").lpf(500)
  .struct("x ~ ~ x ~ ~ x ~")          // tresillo-ish bass rhythm

For non-symbol harmony, write the bass as alternating roots: note("<a1 f1 c2 g1>*2").

Tension and release

• Tension: dominant chords (G7 in C), the v or VII in minor, b2 in phrygian, leaving melodies on non-chord tones, rising filter/register.
• Release: land on i/I, return the melody to a chord tone, drop the register back down.
• Place tension at phrase ends so the loop pulls back to its start — <Am F G E7> resolves home harder than <Am F G C>.

chord("<Am Am F E7>").voicing()   // E7 makes the loop "lean" back to Am

Melody-writing heuristics

1. Mostly stepwise — adjacent scale degrees; melodies are lines, not dice.
2. Leap, then resolve — after a jump (4+ degrees), step back the other way.
3. End phrases on chord tones (root/3rd/5th of the current chord).
4. One rhythmic motif, repeated with variation — change pitch, keep rhythm.
5. Leave rests — phrases need breath; ~ is a note choice.

// motif (cycle A) and varied answer (cycle B): same rhythm, new contour
n("<[0 1 2 ~ 4 ~ 2 0] [0 1 2 ~ 5 ~ 4 2]>")
  .scale("D:dorian").s("triangle").gain(.55)

Pentatonic + off echo is a near-foolproof lead:

n("0 ~ 2 4 ~ 4 7 ~").scale("A:minor:pentatonic")
  .off(1/8, x => x.add(note(7)).gain(.5))

Call-and-response

Two shapes:

// A) alternate phrases per cycle: call, then answer
n("<[0 2 4 ~] [4 2 1 0]>").scale("G:mixolydian").s("piano")

// B) off() answers automatically, transposed and panned
n("0 ~ 3 ~ 2 ~ ~ ~").scale("E:minor:pentatonic")
  .off(1/2, x => x.add(note(7)).pan(.8).gain(.6))

Quick cautions

• n() without .scale() selects samples, not pitches.
• note("0 2 4") is MIDI 0/2/4 — inaudibly low. Use n()+scale or note names.
• Transpose by semitones with .transpose(n), by scale steps with .scaleTranspose(n); .add(n) on n() patterns moves by degrees.
• Test exotic scale/chord names in the REPL — unknown names fail silently.

Deep reference: knowledge/tonal-and-theory.md.