[Elecraft] [K3] what audio passband should I expect in TX DATA/DATA A mode?

[Pierfrancesco Caci]

Hello,
I'm dabbling with wsjtx, and I see that my rx audio has some definite roll
off at <300 Hz and >3500 Hz. Selected filter is the 12 kHz one, and
width is set to 4 kHz. Audio soundcard is the Numark studio-io, but I
also saw this with an el-cheapo adapter. 
Also, I see the same roll-off in fldigi, so the final application should
not matter. 
Am I doing something wrong? What should be the audio passband available
at line out connector?

Thanks

Pf

-- 
Pierfrancesco Caci, ik5pvx