Creative SB0350 Hardware Programming Guide - Page 69

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Mixer Chip Programming 4-11 Microphone Automatic Gain Control (AGC) Helps to maintain the mic input signal at a reasonable level. Gain Control Independent 4-level gain control on each of the left/right input/output mixing paths. Tone Control Independent 16-level bass and treble control on the left and right output mixing paths. CT1745 features dynamic filtering. There is no need for filter controls as in the CT1345. There is also no need for the Stereo Switch bit as on the CT1345, which has to be set to enable stereo digitized sound output. Another difference is that the Mic volume control now genuinely affects the signal amplitude for recording; on CT1345, it only affects the output level. Register Functions Besides the detailed register map, logical schematic diagrams of the input and output mixing paths are also included to aid in understanding the mixer chip. The following notations are used to describe the detailed register map of CT1745: „ „ ".L" stands for left channel and ".R" stands for right channel. Individual control elements are tagged with a "0xRR:D" label on the logical schematic diagrams. 0xRR is the mixer register number in hexadecimal. D is the particular bit within the register that controls the setting. If ":D" is missing, it means the entire register is dedicated to that control. The grayed areas of the table represent reserved bits. „

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Mixer Chip Programming
4-11
Microphone Automatic Gain Control (AGC)
Helps to maintain the mic input signal at a reasonable level.
Gain Control
Independent 4-level gain control on each of the left/right input/output mixing paths.
Tone Control
Independent 16-level bass and treble control on the left and right output mixing
paths.
CT1745 features dynamic filtering.
There is no need for filter controls as in the
CT1345.
There is also no need for the
Stereo Switch
bit as on the CT1345, which
has to be set to enable stereo digitized sound output.
Another difference is that the
Mic volume control now genuinely affects the signal amplitude for recording; on
CT1345, it only affects the output level.
Register Functions
Besides the detailed register map, logical schematic diagrams of the input and output
mixing paths are also included to aid in understanding the mixer chip.
The following notations are used to describe the detailed register map of CT1745:
±
“.L” stands for
left
channel and “.R” stands for
right
channel.
±
Individual control elements are tagged with a “0x
RR
:
D
” label on the logical
schematic diagrams.
0x
RR
is the mixer register number in hexadecimal.
D
is
the particular bit within the register that controls the setting. If “:
D
” is
missing, it means the entire register is dedicated to that control.
±
The grayed areas of the table represent reserved bits.