Motor said:
I'm looking at 2 new mid-tower cases. One has I/O jack that supports
AC97 audio and the other supports HD Audio. I'm confused as to which one
is most necessary? If it supports one, does it support the other? (I've
seen one with the following: 'supports AC97/HD Audio'). Would this be 2
separate connections to the motherboard? I just listen to cd's and
mp3's. My granddaughter watches the occasional DVD. Thanks for suggestions.
The answer to your question would be, the HDAudio defined tower, will
support any new motherboard, but would not be as convenient for a
ten year old motherboard.
The tower with AC'97 will work with older motherboards or new ones,
at least as long as the industry continues to support dual mode
operation of the FP_AUDIO header on the motherboard. All my cases
here are wired AC'97, and I do have a few HDAudio motherboards with
dual mode front panel wiring operation. And I haven't seen a rush
to doing HDAudio wiring only, at least when people ask this particular
question. I'd still seeing the motherboards having support for
dual mode wiring, and the cases are still mostly AC'97 wired.
It really should not matter which you use. If you have no interest
in putting ancient motherboards in that tower, then the HDAudio tower
should be fine. While the other one could be used for either purpose, old
or new.
Some cases come with two cable assemblies, and you can use the
one most appropriate for your motherboard (HDAudio cable assembly
for modern boards, AC'97 assembly for older ones.) All they're
doing in that case, is disconnecting a few wires from the AC'97
cable.
*******
An older motherboard, had an AC'97 pinout which would work with your AC'97
case wiring.
Newer HDAudio motherboards may support both AC'97 and HDAudio *wiring* for the
front panel, but the trick there is, the AC'97 pinout definition is
"simplified", such that it is a subset of the HDAudio pins. In other words,
the AC'97 wiring on an HDAudio CODEC equipped motherboard, isn't the same
exactly as the AC'97 wiring on an older motherboard. That is how they
arrange them to share the same pins.
The end result is, the majority of computer cases support AC'97 wiring
(full or reduced definition). If you have a "solid block" 2x5 cable
assembly, rather than individual wire plugs, then pulling some of the
wires out of the solid block, to meet the comments in the middle
column below, is recommended. The individual wires scheme is more
flexible - you don't hook up the wires you don't need.
There hasn't been a complete switchover to pure HDAudio wiring. In part,
this was caused by the need for jacks with isolated side contacts, and
I didn't see any of those when I went shopping for some. They didn't seem
to be distributing them. I view that as a "chicken versus egg" situation,
where the case manufacturers didn't want to make any mistakes.
In terms of giving pinouts, I'm missing one of the documents I've used
in the past, and since the document was just a number, my odds of finding
it again are just about zero. In any case, these examples are to illustrate
the differences, if any.
Traditional AC'97 Modified AC'97 HDAudio
----------------- (for dual mode) (dual mode or otherwise)
MIC2 AGND MIC2 AGND Port1_L AGND
MICBIAS +5VA MICBIAS ??? Port1_R PRESENCE#
FPOUT_R RET_R FPOUT_R --- Port2_R SENSE1_RETURN
HP_ON ??? Sense_Send
FPOUT_L RET_L FPOUT_R --- Port2_L SENSE2_RETURN
(When not used, had (No jumpers needed (Port names reflect the retaskable
two jumper plugs, to on header. No return nature of the jacks. PRESENCE#
join FPOUT to RET. signals are needed. signal is grounded, if a real
HP_ON and +5VA were Power removed for HDAudio cable assembly is being
for an optional non-existent headphone connected.)
headphone amplifier.) amplfier. Only five
wires should really be
connected, for fault
free performance! Leave
the return wires dangling.)
The "sense scheme" for HDAudio is shown on page 172 here.
ftp://download.intel.com/standards/hdaudio/pdf/HDAudio_03.pdf
The modern front panel audio wiring options are shown here.
Page 20 and Page 23. Page 20 is a form of modified AC'97,
but I wouldn't build a motherboard using that diagram
verbatim. Since Sense_Send shares the pin, you wouldn't
tie a hard +5V to that pin for example. I don't know
what Intel was thinking, when they did page 20. In any
case, you can see the inspiration provided by page 20,
reflected in the middle column above.
http://www.formfactors.org/developer/specs/A2928604-005.pdf
The older pure AC'97 pinout is shown on page 20 here for reference.
(This defines the older, leftmost column above.)
http://web.archive.org/web/20040407...org/developer/specs/fpio_design_guideline.pdf
The three sense pins on the HDAudio are wired in the computer
case, to the two isolated side-contact switches on the
headphone and microphone jacks. They would look like this.
The front panel wiring assembly contributes the two switches to
this picture, while the resistors used to encode things are
on the motherboard itself.
/
+--/ x--+
--------------------+ | |
| | X---- resistor --- GND
CODEC Sense_Pin ------+-----X
chip | | | X---- resistor --- GND
--------------------+ | | |
| +--\ x--+
| \
|
v
To two other jack
detection circuits on the
motherboard
The front 1/8" stereo jacks have three contacts. The function and wiring
are summarized in this table.
TIP RING SLEEVE
Headphone LEFT RIGHT GND
Microphone (mono) MIC MICBIAS GND (MICBIAS is weak power for electrets,
and will not harm other things.)
Microphone (stereo) MIC_L MIC_R GND (Separate bias is connected to
both channels, to power stereo
electrets, and will not harm other
things. Example. Andrea Superbeam.)
http://www.andreaelectronics.com/Buy/ProductDesc/Superbeam_Array.htm
HTH,
Paul
