...chiming in a little late on this topic.... I tend to play most (if not all) my Joni renditions in standard tuning, working them out usually by taking the chord name as it is written (rather than the fingering shapes as they are illustrated in the books) to 'build' the chord up.
I'm finding increasingly that she uses a lot of 9ths and 'suspended' notes - forgive my terminology, I'm not at all educated in this subject - on fairly basic chords and, so long as you don't try full strumming, can capture a fairly honest representation of the original. You can even get some 'ringing' open strings to add to the flavour. Just last night I was working on Passion Play in 'standard' and am, so far, really pleased with the sounds I'm making........ ....but when all is said and done, standard tuning will never match the open tunings with Joni's songs. It can't really hope to but trying appeals to my Calvinist/hair-shirt sensibilities....LOL. Les (London)
