4-6
Mixer Chip Programming
CT1345 Mixer
This section describes the features and register functions of the CT1345 mixer chip
used on the Sound Blaster Pro card.
Features
CT1345 is a stereo mixer that controls volume, output mixing, and input source
selection as well as the input and output low-pass filters. It also controls the stereo
voice data output.
Volume Control
CT1345 provides independent 8-level volume control of both stereo channels for the
Master, Voice, MIDI, CD, and Line-in sources.
The Microphone output mixing source is mono with 4-levels of volume control.
This control will not affect the amplitude of a recorded signal but only affects the
output mixing level.
Output Mixing
The output mixing path takes signals from the Voice, MIDI, CD and Microphone, as
well as the PC Speaker. To silence a source, you can either reduce the source
volume to zero, or terminate the source activity.
Input Source Selection
CT1345 allows input source selection of either CD, Line-in or Microphone sources.
The default input source is Microphone.
Input and Output Filter Control
Low-pass filters are available on the CT1345. There are 3.2 kHz and 8.8 kHz filters
for input. For output, only the 3.2 kHz filter is available.