Oki 5400 - Manual (Page 81)

Programming 73
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is
h TONE FOR ECHO: This function compensates for poor overseas line
conditions. Available settings are on and off.
MH ONLY: This function controls the type of compression method your
fax machine uses during communication. Adjusting may also help in poor
line conditions. Available settings are on and off.
H/MODEM RATE: This function controls the communications speed
your fax machine’s modem uses at the beginning of a fax communication.
Available settings are 28.8K,14.4K, 9.6K and 4.8K.