Editing Intel High Definition Audio (section)

==Front panel connector==
Computer motherboards often provide a connector to bring microphone and headphone signals to the computer's [[front panel]]. Intel provides a general specification for this process, but the signal assignments are different for both AC'97 and HD Audio headers.<ref name="Intel FP">{{Citation |last=Intel Corporation |url=http://www.formfactors.org/developer/specs/A2928604-005.pdf |title=Front Panel I/O Connectivity Design Guide |date=February 2005 |version=Version 1.3 |pages=19&ndash;25 |access-date=2011-11-04 |archive-url=https://web.archive.org/web/20110511144045/http://www.formfactors.org/developer/specs/A2928604-005.pdf |archive-date=2011-05-11 |url-status=dead }}</ref>

The pin assignments for the AC'97 and HD Audio connectors are:<ref name="Intel FP"/>{{rp|21,22}}
{| class="wikitable"
|-
! rowspan=2 | Pin
! colspan=2 | AC'97
! colspan=2 | HD Audio (HDA)
|-
! Signal
! Description
! Signal
! Description
|-
| 1 || MIC || {{unbulleted list
 | Audio, mono, in (mic. level)
 | Audio, left, in (biased, mic.level)
}}
| PORT 1L || Audio, left, port 1
|-
| 2 || AUD_GND || Ground
| GND || Ground
|-
| 3 || MIC BIAS || {{unbulleted list
 | Microphone bias
 | Audio, right, in (biased, mic. level)
}}
| PORT 1R || Audio, right, port 1
|-
| 4 || AUD_GND || Ground
| PRESENCE# || HDA dongle/connector detection, active low
|-
| 5 || FP_OUT_R || Audio out, right, out (headphone-level capable), front panel
| PORT 2R || Audio, right, port 2
|-
| 6 || FP_RETURN_R || Audio, right, return (when jack is unconnected), front panel
| SENSE1_RETURN || Port 1 jack detection
|-
| 7 || AUD_5V || Power, +5&nbsp;V
| SENSE_SEND || Jack detection sense, resistance multiplexed
|-
| 8 || KEY || {{n/a|Not present, physical key}}
| KEY || {{n/a|Not present, physical key}}
|-
| 9 || FP_OUT_L || Audio, left, out (headphone-level capable), front panel
| PORT 2L || Audio, left, port 2
|-
| 10 || FP_RETURN_L || Audio, left, return (when jack is unconnected), front panel
| SENSE2_RETURN || Port 2 jack detection
|}

The HD Audio 3.5&nbsp;mm subminiature audio jack differed from connectors used in the AC'97 specification and in general audio equipment. The AC'97 used a regular 3.5&nbsp;mm audio jack, which typically has 5 pins: one pin for ground, two pins for stereo signal, and two pins for the return signal.<ref name="Intel FP"/>{{rp|20}} When no plug is connected, the two stereo signals are connected to their return pins. When a plug is inserted, the stereo signals contact the respective channels on the plug and are disconnected from the jack's return pins. The HD Audio 3.5&nbsp;mm jack does not have the two return audio signals; instead, it has an isolated switch that senses the presence of a plug in the jack.<ref name="Intel FP"/>{{rp|25}}

In the AC'97 design, the audio output is sent to the jack by default. When a headphone is detected, the return signal pins for the speakers are disconnected, directing the audio to the headphone. The jack redirects the audio to the speakers if no headphone connection is detected. Similarly, the return pins ground the microphone jack connection if no microphone detected. As a result, most motherboards with AC'97 audio require two [[Jumper (computing)|jumper]]s to short these pins if no front panel audio module is connected, so audio passes to the speakers.<ref name="Intel FP"/>{{rp|21}}

In the HD Audio design, the codec sends the audio directly to the speakers if a plug is not inserted. When a plug is inserted, the isolated switch inside the jack informs the motherboard, and the codec sends audio to the headphones. A similar isolated switch is used to detect when a microphone has been plugged in. HD Audio can also sense the presence of an audio [[dongle]]. A 10&nbsp;kΩ pull-up resistor is attached to pin 4 ({{mono|PRESENCE#}}). When the HDA dongle is plugged in, it pulls pin 4 to the ground with a 1&nbsp;kΩ resistor. The motherboard can determine if a dongle is connected by examining the logic level on pin 4. If the motherboard does not detect a HDA dongle, it should ignore the {{mono|SENSE1_RETURN}} (pin 6) and {{mono|SENSE2_RETURN}} (pin 10) signals.<ref name="Intel FP"/>{{rp|24}}

Intel warns that HDA dongles should be used with HDA motherboards:<ref name="Intel FP"/>{{rp|19}}
{{blockquote |It is strongly recommended that motherboard designers only use Intel HD Audio analog front panel dongles with the Intel HD Audio analog front panel header to ensure that the jack detection and dynamic retasking capability are preserved.  Passive AC'97 analog front panel dongles (ones that leave the 5V Analog pin-7 line unconnected on the dongle) may be used with the Intel HD Audio analog front panel header.  But note that the front panel jack detection and re-tasking functionality will be lost as the AC'97 jacks cannot support connection to the SENSE line.  In addition, software must be aware that an AC'97 dongle is being used with an Intel HD Audio analog header since the software might need to dedicate codec ports that are connected to the header to meet the product's intended functionality.}}

The different signal assignments can cause trouble when AC'97 front-panel dongles are used with HDA motherboards and vice versa. An AC'97 dongle returns audio on pins 6 and 10 rather than digital plug sensing signals. Consequently, a loud audio passage may cause a HDA motherboard with a AC'97 dongle believe headphones and microphones are being plugged and unplugged hundreds of times per second. An AC'97 motherboard with an HDA dongle will route the AC'97 5&nbsp;V audio supply (pin 7; silence) to the speakers instead of the desired left and right audio signals. To avoid this, some motherboards allow choosing between HDA and AC'97 front panels in the BIOS. Even though the actual audio hardware is HD Audio, the BIOS can be manipulated to allow the use of an AC'97 front panel. Likewise, some modern enclosures have both an "AC'97" and an "HDA" plug at the end of the front-panel audio cable.{{citation needed|date=September 2022}}