US Robotics 33600 User Manual page 39

In the following paragraphs, you will find some indications
pertaining to the settings of voice applications in order to use the
modem.
Input/Output Source Selection
Set the recording or playback sources as the devices from which
you are going to record the local message and listen to the
received messages. (External powered speakers, microphone,
headset or sound card)
Recording and Playback Quality
The greater the sampling rate, the better the quality of the
message is. This also means also that the message file size on
the disk will be greater. For example, 10 seconds recorded on 2
bits equals about 18 kbytes, whereas a message with twice the
quality (4 bits) will require, for 10 seconds, about 36 kbytes.
Level and Length of Silence
Aside from the various adjustments to recording or playback
levels, there are usually two of them that relate to the silence.
These settings are used, one to set the 'minimum noise' level on
the line that the modem can consider as silent, the other the
maximum length of silence before going on hook.
Sportster Winmodem 33600 & x2/56K - User's manual 35