SigmaTel, Inc.
Data Sheet
STAC9721
20
04/07/00
04/07/00
Table 6. Mixer Functional Connections
Source
Function
Connection
PC_Beep
PC beep pass thru
from PC beeper output
PHONE
speakerphone or DLP in
from telephony subsystem
MIC1
desktop microphone
from MIC jack
MIC2
second microphone
from second MIC jack
LINE_IN
external audio source
from line-in jack
CD
audio from CD-ROM
cable from CD-ROM
VIDEO
audio from TV tuner or video camera
cable from TV or VidCap card
AUX
upgrade synth or other external source
internal connector
PCM out
digital audio output from AC'97 Controller
AC-Link
LINE_OUT
stereo mix of all sources
To output jack
LNLVL_OUT
Additional stereo mix of all sources
To output jack
MONO_OUT
MIC or mix for speakerphone or DLP out
to telephony subsystem
PCM in
digital audio input to AC'97 Controller
AC-Link
4.1 Mixer Input
The mixer provides recording and playback of any audio sources or output mix of all
sources. The STAC9721/23 supports the following input sources:
• any mono or stereo source
• mono or stereo mix of all sources
• 2-channel input w/mono output reference (mic + stereo mix)
* Note: any unused input pins should be tied together and connected to ground with a
capacitor (0.1
µF suggested), except the MIC1 and MIC2 inputs which require their own
0.1
µF capacitors to ground if not used.
4.2 Mixer Output
The mixer generates two distinct outputs:
• stereo mix of all sources for output to the LINE_OUT
• stereo mix of all sources for output to the LNLVL_OUT
• mono, MIC only or mix of all sources for MONO_OUT
* Note: Mono output of stereo mix is attenuated by -6 dB to prevent clipping when left
and right channels are combined.
4.3 PC Beep Implementation
PC Beep is active on power up and defaults to an un-muted state. The user should mute
this input before using any other mixer input because the PC Beep input can contribute
noise to the LINE_OUT during normal operation.
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