High bass is the minimum viable cross-tuning. The lowest course comes up a whole tone and nothing else moves at all, which buys you an A ringing underneath a tune in A for the price of turning two tuners. Compared with cross A, which moves two courses and four strings, this is almost free.
The retune, course by course
Derived from pitch arithmetic against standard GDAE — one row differs from standard, and that is the whole tuning:
| String | Standard | High bass | Semitones |
|---|---|---|---|
| 4 | G3 | A3 | up 2 |
| 3 | D4 | D4 | stays |
| 2 | A4 | A4 | stays |
| 1 | E5 | E5 | stays |
ADAE — 1 course moves (4).
What the open strings spell
The distinct letters now sounding are A, D, E, which reads as Dsus2 or Asus4. Three letters rather than two, and unlike its neighbours on this site the set does stack: it is a genuine suspended chord, readable from either end. That is the audible difference between high bass and full cross A. There is still no third, so nothing here is major or minor — but there is a fourth-and-fifth structure with a real root, and tunes sit on it differently.
One course, two strings, minimal risk
Only the low course moves, and only upward by a tone — two strings, on the heaviest pair, which take that change without complaint. This is the cross-tuning to try first if you have never retuned a mandolin, because the failure mode is small and reversing it takes thirty seconds. It is also the only one on this page you could reasonably do mid-set.
What survives
The standard chord library does NOT apply here — a fretted course moved, so every fret in it that touches that course is off by the course’s delta. But look at how little is affected: courses 3, 2 and 1 are untouched, which is three quarters of the instrument. Every shape on the chord pages that stays off the lowest course is still exactly right, and on a mandolin a great many of them do. Only the bottom course is a whole tone out.
That makes high bass the one tuning here you can half-commit to: keep playing your usual shapes on the top three courses, and treat the low A as a drone you strike rather than a course you fret. Fiddle Warrior’s high bass page takes the same tuning from the bow’s side, where a single re-tuned string changes which double stops ring.