Detuning a bass is arithmetic, and arithmetic can be shown rather than asserted. Which strings move, by how many semitones, what the open set spells once they have, and how much of your fretted vocabulary survives all follow from the instrument’s own pitches. So on this site they are derived from those pitches, and the only thing typed by hand on any of these pages is each tuning’s list of target note names. Every number below falls out of that list.
The three tunings
| Tuning | Strings | Moved | Open strings read as |
|---|---|---|---|
| Drop D | DADG | 1 | Dsus4 or Gsus2 |
| Half step down | D#G#C#F# | 4 | no triad at all |
| Drop C | CGCF | 4 | Csus4 or Fsus2 |
Reach, or register
Bassists retune for two unrelated reasons, and the three tunings here split cleanly between them. Drop D and drop C buy reach: a note below the open E that the neck simply does not own, sitting on an open string where it rings longest and costs nothing to fret. Half step down buys register: it moves the whole instrument a semitone without changing a single interval, which is what a singer means when they ask the band to drop a half step.
The difference shows in the moved column. A reach tuning moves one string further than the others and breaks the symmetry of the neck; a register tuning moves every string by the same amount and keeps that symmetry perfectly. Nothing you know about intervals changes in the second case. Quite a lot changes in the first.
What a retune costs
Every semitone down is tension you gave away, and tension is what makes a bass string speak. Drop far enough on a short-scale instrument and the low string starts to flap against the frets rather than ring. That is a physics problem, not a technique problem, and it is solved with gauge and scale length rather than with a lighter touch — the strings guide covers the first and the scale-length guide the second. A 35-inch five-string holds drop C without complaint; a 30-inch short scale in the same tuning is a different conversation.
What stops being true
Every shape on the bass chord pages is fretted against standard EADG, so the moment a string moves, any shape that touches it is wrong by exactly that string’s delta. The per-tuning pages name the strings that did not move, which is the useful half of the answer: a shape that never touches a moved string is untouched. In drop D that is most of what you play. In drop C it is nothing at all.
Retune, or move your hand
A retune changes what the open strings are. Transposing changes where your hand goes. They solve different problems, and the honest reason to prefer a retune is almost always the open string itself — the low D you can let ring under a riff, or the pedal tone you cannot hold down and play over at the same time. If you only need the pitch, the scale maps will get you there in standard without touching a machine head.