Audio ports on a motherboard explained

How do they work?

These days when building a computer system, most people are interested in the specs of the mainboard. After all it is the main component that connects every other component inside the enclosure. It solely determines what type of CPU and RAM you will be using, and what space you have available for additional components.

Not many are concerned much with the audio specs as these days they are pretty much well integrated into many new motherboards and come standard with a minimal of 6 channels unless you buy a very cheap integrated board which will at least have stereo sound. The sound chip is usually made by one of the major semiconductor SoC vendors like Realtek, Creative or Intel and is integrated on the board and has external ports for device attachment.

Various types of audio ports on motherboards

When connecting audio hardware like a speaker system, microphone or Tape/CD recorder to a PC, one of four ports can be used which are:

• 3.5mm TRS audio jacks
• S/PDIF TOSLINK port
• S/PDIF Coaxial RCA port
• 6.35mm TRS audio jack

3.5mm TRS Audio Jacks

This is an analogue, older, yet still one of the most common interfaces for audio hardware on motherboards. Since Microsoft and Intel compiled the "PC System Design Guide" in the late 90s, motherboard manufactures have used this guide in their designs, which specifies three colors namely, Pink, Green and Blue for these TRS (Tip, Ring, Sleeve) jacks.

Though modern designs can deviate sometimes due to preferred design themes on their higher end motherboards, in that case, the ports are usually clearly labelled on the back plate or user manual.

Analogue audio ports (8-channel) Image credit: Eric Kilby CC BY-SA 2.0.

The Green jack is a stereo "Speaker Out" or "Line Out" connection, used for connecting a traditional speaker system or amplifier using a 3.5mm - 3.5mm or 3.5mm - L/R RCA stereo audio cable. Headphones can also be connected to it.

The Pink jack is the "Microphone" or "Mic In" connection, used for connecting a traditional wired microphone with a 3.5mm audio cable attached to it. It should not be used as "Line In" to avoid damage to the board (see below)

The Blue jack is the "Line In" or "Audio In" connection, used for connecting a CD/Tape deck or other line level audio device like a mixer, usually for recording audio on the computer. This jack is normally less sensitive than the mic jack to handle the higher voltage from the line out of other audio devices. As a result it is safest to connect such equipment using this instead of the Pink jack to avoid distortion and possible damage to the board. If a mic is connected here the volume level can be very low.

Expansion of the analogue 3.5mm audio jacks

As multi-channel surround sound evolved, manufacturers included three additional color-coded jacks to their boards. These are primarily outputs for 5.1 and 7.1 surround sound systems which comprise additional channels of audio. They include a Black, Orange and Gray port.

The Orange port is the "Center/Sub" output connector, used for connecting the center channel speaker and the subwoofer. Since these are both single channel, the TRS stereo jack usually carries Center on right and Sub on left or vice versa.

The Black port is the "L/R Rear" output connector, used for connecting the stereo rear channel speakers. Since these are stereo signals this TRS stereo jack carries rear Left and rear right signals (+/-) to L/R rear speakers.

The Gray port is the "L/R Side" output connector, used for connecting the stereo side channel speakers. Since these are also stereo signals this TRS stereo jack carries surround Left and surround right signals (+/-) to L/R side speakers. This jack is only used in an 8 channel surround setup (7.1).

Some computers have a front audio panel in which the ports are Green and Pink. These facilitate easy connection to smaller speakers or headphones as well as a microphone. This panel usually connects via a cable to an internal audio header soldered on the motherboard itself.

S/PDIF Connectors

With the rise in popularity of digital audio like CDs/DVDs and surround sound in Home theater systems, this port is used a lot these days to connect high end computer speaker systems to enjoy cleaner quality digital audio.

S/PDIF TOSLINK connector (upper left) with 6-channel analogue audio

The TRS audio jacks explained above are analogue signal ports meaning their electrical signals vary in voltage levels and go directly to an amplifier's input such as in older speaker systems. The S/PDIF (Sony/ Phillips Digital Interface) is however digital audio transmission which also connects to an appropriate port on your speaker system but uses something called a DAC (Digital to Analogue Converter) because in the real world electrical audio signals used to drive loudspeakers are analogue. The DAC is usually built into the speaker system's preamplifier section.

Types of S/PDIF jacks

S/PDIF come in 2 different types of connectors, TOSLINK and Coaxial RCA connectors. TOSLINK cables, transmit audio signals via optical fiber rather than regular metal conductors found in RCA cables. Regardless both transmit identical quality digital signals to the speaker systems. TOSLINK is more suited for shorter more direct runs with less bends due to the optical medium.

S/PDIF RCA port (yellow) with TOSLINK below

Being a digital standard, it adheres to a protocol and therefore is effective in transmitting multi-channel audio using a single TOSLINK or Coaxial RCA cable. If a motherboard has RCA S/PDIF, it will usually be a single yellow or orange RCA port. If it has a TOSLINK port, most of the times it's black and covered. This port can transmit Dolby Digital and DTS surround (5.1 and 7.1) digital audio and is common with HTPCs. Modern boards and compact PCs usually have the TOSLINK vs the RCA.

6.35mm TRS audio jack

Motherboards that have this port are very rare to see. Usually they are aimed at audiophiles who have high-end headphones that require a higher power to drive them and the jack being larger can carry the heavier current without heating up. Usually these audiophiles nowadays use something called an "audio interface" connected via USB so this ports isn't common on motherboards.

6.35mm TRS headphone port with blackout audio jacks with labels and single color showing main output

Conclusion

Back in the day, a sound card connected to the motherboard was required for good audio but it's rarely the case nowadays unless you're an audiophile. Anyway, it's always good to have basic knowledge of the connectors on your motherboard when building a system of trying to make any connections you aren't familiar with. Hopefully this guide sheds some light regarding the audio aspect of such and it helps you better understand the use of each audio port.