rockadanny - I read (in TAS I think) that 3db is not detectable to the human ear and that 10db sounds like double the volume even though 3db is actually double when instruments are used.
Good critical ears can detect about 0.2 db SPL differences provided it is over a broad range of frequencies in the midrange (as would be the case with volume). Adjustment of treble, for example, by 0.2 db SPL is probably not audible for most people - around 1 db SPL change in treble would become audible to many.