A 4-string bass is usually tuned to E, A, D & G--one octave below the 4 lowest strings of this
On a standard tuning bass guitar, the strings are 
tuned, from ... On a standard tuning bass guitar, the strings are tuned, from lowest 
to ... A six string bass is usually B0-E1-A1-D2-G2, but might also range from F#0 
to D2 ... gauge E string (tuned two half-steps down), a medium A string, a light D... [DOC] [TLE] Have you tried B-E-A-D tuning on your 4-string bass?