As you can imagine, the 3429 symbol rate of V.34 requires about 3429 Hz of
bandwidth to the 3 dB points, therefore with a low frequency cut-off of 244
Hz and a centre frequency of 1950 Hz, one needs a high frequency cut-off of
3672 Hz, which is higher than the 3400 Hz 3 dB cut-off of S12-S12
connections and still higher than the 3500 Hz 3 dB cut-off of AXE-AXE
connections.

The V.34 probe tones of 3450 Hz and 3600 Hz some-how have to figure out the
high frequency roll-off of such a connection...

--- msgedsq 2.1