Audio Codec '97

AC ‘97 Component Specification Revision 2.3 Rev 1.0
40
audio sources, regardless of Controller architecture (host-based or hardware-accelerated Controllers).
Double-rate audio. Support is also defined for optional 88.2 or 96 kHz DAC operation. Current PC-based DVD
implementations recommend 96 (or 88.2) kHz audio to be down-sampled to 48 (or 44.1) kHz for high quality
rendering. However, output slots 10-12 (or optionally slots 7, 8) have been assigned as optional n+1 sample carriers
in order to enable double-rate operation on front (L, C, and R) DAC channels with up to 20-bits (120 dB dynamic
range) at 88.2 or 96 kHz. Surround and LFE channels remain limited to 48 kHz with up to 20-bits.
5.4 Multichannel Audio
AC ‘97 assigns AC-link output slots 6-9 for optional multi-channel analog audio. Slots 7 and 8 are dedicated to
Surround Left and Surround Right, while Slots 6 and 9 are the Center and LFE channels, respectively. This
capability can be used to support multi-channel output from applications such as games, or output multi-channel
sound from multi-channel encoded sources such as DVD. This capability can be used in place of, in co-operation
with, or entirely independent of, an independent digital stream that may be present on the S/PDIF stream.
5.4.1 Primary Codec Multichannel Audio
A single monolithic AC ‘97 Codec can support up to 6 channels of analog audio plus fully concurrent S/PDIF using
slots 3, 4, 6, 7, 8, 9, 10, and 11 as shown in Figure 16. Volume and mute controls are provided by Registers 02h (L
& R), 38h (L & R Surround), and 36h (Center & LFE).
PCM out DACs
(2 or more* channels)
L Front DAC
AC-li nk
slot
3
4
7
8
6
9
R Front DAC
L Rear DAC*
R Rear DAC*
CNTR DAC*
LFE DAC*
S/PDIF*
10
11
S/PDIF is programmable
to first available slot pair
(3&4, 7&8, 6&9, or 10&11)
Figure 16. Primary Codec Multichannel implementation
5.4.2 Secondary Codec Multichannel Audio
AC ‘97 also defines support for multichannel implementations using multiple AC ‘97 Codecs. Standardized
Controller/Codec interoperability (requiring no access to vendor specific registers) depends on two key capabilities:
• mapping of AC-link output slots to DAC functions based on Codec ID
• DAC management, Volume Control and synchronization across multiple Codecs
Intel’s recommendation for multiple audio Codec implementations is that the same Codec vendor provides all
Codecs. Support for cross-vendor multiple Codec multichannel audio depends on compatibility on details of
specific Codec implementation, some of which are not fully addressed by the AC ‘97 specification.
The following is a partial list of potential cross-vendor multiple Codec multichannel audio compatibility issues
• synchronization
• slot request behavior, start and stop, queue depths, etc.