Chord inversions and voice leading

Any chord tone can be the lowest note. Take minor 0 3 7, move the bottom note up an octave and re-measure from the new lowest note:

Major: 0 4 7 → 0 3 8 → 0 5 9 (source: s-037-lab).

Why it matters in chip music#

• Voice leading: moving between chords sounds smoothest when each note travels a short distance; inversions let chords share or nearly share notes.
• Top-note control: a fast chord-arpeggio is heard mostly by its highest note, which pokes out of the blur. Choose inversions so the top notes of successive chords move by small steps and the chord channel plays a hidden second melody for free. Each inversion needs a different base note in the pattern.

In tracker rows (Greg Heo, 1997)#

root            |C-4 .. ...|E-4 .. ...|G-4 .. ...|
1st inversion   |E-4 .. ...|G-4 .. ...|C-5 .. ...|
2nd inversion   |G-4 .. ...|C-5 .. ...|E-5 .. ...|

"Inversions are very important to break the monotony of having every single chord in root position" (source: s-tw074-intro-to-musical-theory).

Voicing a whole progression (Necros, 1995)#

necros's "art of voicings" turns C – F – Dm – G, tracked as root-position triads on rows 0/8/16/32 at speed 6 ("about as interesting as a night spent hanging out in #ansi"), into C9 | Fadd2/C | Dm7 | Gsus4–G with five channels (source: s-tw018-advanced-tracking-tips-iii):

Rules from it: avoid stacking notes a scale step apart (C–D, E–F, G–A) unless you want the rub — an octave between them widens the interval and eases the ear; less voice movement in a main section keeps the piece from sounding jumpy; and the top notes of the four chords rise E … F … F … G, a motif that gives the progression coherence (the hidden-melody idea above). Learn enough keyboard to try voicings before entering them (source: s-tw018-advanced-tracking-tips-iii).

Inverting an arpeggio is rotating a table#

On a chip the chord is not three channels but one channel cycling through offsets, so an inversion is a rotation of the table rows, plus 12 on whatever moved to the top:

root          0  3  7          A C E
1st inversion 3  7 12    →  or 0  4  9  measured from the new bottom note
2nd inversion 7 12 15    →     0  5  8

Both spellings appear in real tools. sid-wizard keeps chords in a separate table with a note/number display toggle (C=+N) and a negate key (=), so the same instrument can play a chord and its inversions as different chord entries (source: s-sid-wizard-charts-and-tables); goattracker's wavetable right byte holds the offsets directly, 00–5F up and 60–7F down, so an inversion is typed as either a rotation or a negative offset (source: s-goattracker-readme); lsdj's Cxy has only two offsets, so its inversions are the three readings of one triad — C37 versus C49 versus C58 — and anything longer goes in the table transpose column (source: s-lsdj-manual).

Which inversion you choose is audible even at arp speed, because a fast arp is heard by its top note (source: s-037-lab). It can also be chosen to save memory: the Tiny SID 2 512-byte player stores four chords in four bytes as three 2-bit intervals each, and the four it keeps are named for their inversions — %00111000 "1 4 3 – maj7 3rd inversion", %01100100 "2 3 2 – 4 root", %10111000 "3 4 3 – min7 root", %11010000 "min2 root". The inversion was picked so that the intervals fit in two bits (source: s-sidin10-tiny-sid-2-part-1).

On sample trackers the equivalent advice is older and blunter: build chords from separate notes, with inversions, rather than loading a sampled chord — Greebo's rule for sounding professional (source: s-it-hints).

Related#

chord-arpeggio · diatonic-chords · chord-progressions · melody-writing · instrument-tables · semitone-math

Sources#

s-037-lab · s-tw074-intro-to-musical-theory · s-tw018-advanced-tracking-tips-iii · s-sid-wizard-charts-and-tables · s-goattracker-readme · s-lsdj-manual · s-sidin10-tiny-sid-2-part-1 · s-it-hints