The other guides teach parts. This one teaches the space between them — because when a track fails it is almost never because a part was bad. It is because two good parts were in the same register, hitting the same steps, moving in the same direction, or spelling a chord nobody chose. Four relationships, four measurements. The first one is the reason a melody you already wrote can become twelve different pieces of music without changing a note.
The melody below never changes. Not one note, not one rhythm. All that changes is the four chords underneath it — and with them, what every single note is. The same C is a root, then a third, then a ninth, then a note that fights. Watch the labels on the notes change as you switch progression, and listen to the melody become a different piece of music.
Every note is labelled with what it becomes over the chord sounding beneath it. Green is a chord tone, cyan is a colour note, red is a note fighting the harmony.
The thing to notice. A melody sitting on chord tones sounds resolved and slightly plain. The same melody where half the notes land on ninths and elevenths sounds expensive and slightly melancholy — and it is the identical melody. That is not a metaphor, it is what the label on each note is telling you. If a topline you wrote sounds ordinary, the fastest fix is almost never the melody.
How to actually use it: write the melody first, over one chord or none. Then try progressions underneath until the notes you emphasise — the long ones, the ones on beat one — land on the colours you want. A melody note held over a chord change is doing two jobs at once, which is why it is worth choosing the chord change to make it interesting rather than safe.
Two parts either take turns or fight. The measurement is brutally simple: how many steps do both parts hit at the same time? Every collision is two sounds competing for one moment, and the fix is almost always to move one of them a 16th rather than to turn it down.
Red steps are collisions — both parts sounding at the same instant. Interlocking moves the second part into the gaps the first one leaves.
The rule is one line: when one part plays, the other rests. Zero collisions is not the target — a few shared hits are how two parts sound like one band rather than two records. Under about 20% overlap reads as interlocking; over 50% reads as mud, and the number above tells you which side you are on before you have committed to a mixdown fighting it with EQ.
Try "Busy arp". Interlocking does nothing to it — it stays at 25% however you shuffle it, because a part playing on all thirty-two steps has no gaps to move into. That is the real lesson: you cannot interlock your way out of a part that is too dense. The offbeat stab goes from 100% collisions to zero; the busy arp has to lose notes instead.
Two lines moving up together sound like one thick line. Two lines moving in opposite directions sound like two independent voices, and the ear can follow both. This has been the core of counterpoint for four hundred years and it costs nothing to apply to a bassline.
Every transition between two notes is classified by how the parts moved relative to each other.
Parallel fifths and octaves are not a rule you must obey — dance music breaks them constantly and deliberately, because a bass and a lead moving in parallel fifths is one enormous sound rather than two. The point is knowing which you are making. If you want two voices, use contrary motion; if you want one giant voice, use parallel. Doing it by accident is the only mistake.
The same four notes, at different octaves and spacings. Low intervals turn to mud not because of your monitors but because of physics — two notes close together in the bass register beat against each other faster than the ear can separate. There is a chart for this, and it has existed since orchestration textbooks.
Every interval in the voicing is checked against the low-interval limit — the pitch below which that interval stops being heard as harmony and starts being heard as noise.
The practical version: a minor third is fine above roughly C3 and mud below it. A perfect fifth survives down to about B♭1, which is why power chords work in the bass and thirds do not. Below C3, use fifths, fourths and octaves; put your thirds and your extensions above it. Sources vary by a semitone or two, so treat the chart as a starting point and your ears as the arbiter.
| Interval | Lowest advisable root | Approx. frequency | Below that |
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Parts are easy; relationships are the craft. Anyone can write a decent bassline in ten minutes — the other guides in this set will get you there. What separates finished-sounding music from a folder of loops is that every part was written with knowledge of what it would be sitting next to. That is a habit rather than a technique, and this page exists to make the habit measurable.
All audio synthesised live. Harmonic function labels use a simplified chord-scale classification; the low-interval limits are the standard orchestration guideline and vary slightly between sources.