Audio Codec '97

AC ‘97 Component Specification Revision 2.3 Rev 1.0
44
to support full resolution D/A conversions followed by analog attenuation as a means of achieving high SNR.
5.5.2 Analog Mixer Input
The mixer input is a MUX design which offers the capability to record any of the audio sources or the outgoing mix
of all sources. This design is more efficient to implement than an independent input mix, allows the user to apply
3D and tone controls to recordings, and offers simple monitoring when a mix is recorded: “what you hear is what
you get” (WYHIWYG). Mono and stereo mix also provide echo cancellation reference signals.
AC ‘97 supports the full range of input options
9
:
• any mono or stereo source
• mono or stereo mix of all sources
• 2-channel input with mono output reference (microphone + mono mix for mono echo cancellation)
• optional 3-channel input with stereo output reference (microphone + stereo mix for stereo echo
cancellation)
5.5.3 Analog Mixer Feature Detection
5.5.3.1 Minimum Analog Mixer Feature Set
The following describes the minimum required AC ‘97 analog mixer feature set, which all AC ‘97 compliant
Codecs support. Drivers are required to support these analog mixer features, which need no audio driver detection:
• Stereo PCM 16-bit DAC playback with volume and mute
• Stereo LINE IN with volume and mute
• Stereo CD with volume and mute
• Mono MIC with 20 dB boost, volume (programmable gain) and mute
• Stereo LINE_OUT with (master) volume and mute
• Stereo AUX_OUT with optional volume and mute
• Stereo PCM 16-bit ADC record with gain and mute
5.5.3.2 Analog Mixer Cost-Reduction
As audio features migrate to digital, some of the original baseline AC ‘97 analog mixer features will not be needed
in future products. In general, if a feature/function is not implemented the following detection protocol can be used:
Write all 1's to the appropriate AC ‘97 register or bit field; if the register or bit field read-back value reads 0, the
function is not implemented.
New drivers are recommended to specifically test for presence or absence of support for these, now optional, analog
mixer features:
• MONO_OUT (Register 06h, default 8000h)
• PC_BEEP (Register 0Ah, default 0000h or 8000h)
• PHONE (Register 0Ch, default 8008h)
• VIDEO (Register 14h, default 8808h)
• AUX_IN (Register 16h, default 8808h)
• MIC2 (Register 20h, bit 8, default 0)
5.5.3.3 Original Analog Mixer Options
The following AC ‘97 analog mixer features have always been optional to implement, and have feature ID bits in
the Reset/ID (00h) Register. Drivers are recommended to specifically test for presence or absence of support for
these optional analog mixer features:
• Dedicated Mic ADC input channel (Register 00h, bit 0)
• Reserved (Register 00h, bit 1)
• Bass and treble control (Register 00h, bit 2)
• Simulated mono to stereo (Register 00h, bit 3)
9
The audio driver should maintain a persistent record input level for each MUX input option.