Today all motherboards have an embedded sound card (this feature goes by several different names, like on-board audio, on-board sound, integrated audio or integrated sound). In this tutorial we will explain how the on-board audio is produced, allowing you to understand what a codec is and what its importance to the audio quality is.

Some very high-end motherboards don’t come with the audio section on the motherboard, but in add-on card that comes with the product, being installed on a PCI Express x1 slot or on a special connector on the motherboard. This option is used only because some high-end motherboards have already so many connectors on the rear panel of the motherboard that the audio connectors don’t fit there, and using an add-on card solves this problem, as the connectors will now be available at one of the slots of the computer case.

Audio can be available in two different formats: analog or digital. Computers are digital systems so they can only produce and manipulate audio in digital format. The problem, however, is that in the real world audio is an analog entity. Speakers are expecting an analog signal so they can reproduce sounds; you can’t feed speakers with a digital signal – the so called “digital speakers” are in fact analog speakers with a digital-to-analog (DAC) converter converting the digital signal sent by the computer into analog signal. On motherboards there is a chip called codec (short for coder/decoder) that is in charge of converting digital audio signals into analog and vice-versa. This component is very important as it defines the audio quality of a sound card, and we will talk a lot more about it later.

The process of converting the digital signal sent by the computer into an analog signal, so you can hear sound on your speakers – for example, when you play an MP3 file or when you play a video file – is called digital-to-analog conversion or DAC for short. The inverse process, i.e., converting analog sounds sent to the computer through a microphone or through its “line in” input into digital – for example, when you hookup a tape deck or a turntable to your PC to convert old music into MP3 files – is called analog-to-digital conversion or ADC for short.

On any sound card – including those embedded on motherboards – you can find two types of connectors: analog and digital. Analog connectors (usually 3.5 mm mini jacks) allow you to connect your sound card directly to speakers (i.e., “analog speakers”). This is the cheapest and easiest way to connect speakers to your PC.

Digital connection, also known as SPDIF (Sony/Phillips Digital Interconnect Format) can be found in two flavors, coaxial (using a mono RCA connector) or optical (using a connector called Toslink). This connection allows you to connect your sound card to home theater receivers and digital speakers. As we have already explained, loudspeakers are analog devices. Home theater receivers and digital speakers have a digital-to-analog converter inside that converts the digital signal received into analog and then send the signal to the speakers.

Digital connection provides some advantages compared to analog connection. First, usually home theater receivers and digital speakers use a better codec than the one used on the motherboard and because of that the audio quality is higher (lower noise level, mainly). Secondly, home theater receivers and digital speakers may provide features not found on analog speakers, like Dolby Pro Logic, which simulates surround sound when the original sound source is just stereo (i.e., two channels only) – using analog speakers you can only have this kind of feature if the software you are using provide them. And in third place, with digital connection you need just one cable to connect your PC to your home theater or digital speakers, while with analog connection you need one cable for each pair of speakers (on a 5.1 system you will need three cables, for example).

The drawback of digital connection is price, as the components involved with digital connection are more expensive (the cost of a home theater receiver and a set of speakers is far higher than the cost of a set of analog speakers for your PC), the reason being the use of a more expensive codec and also the cost of the decoders for several additional enhancements, like the abovementioned Dolby Pro Logic.

In Figure 1, you can see the connectors found on the rear panel of a motherboard (ASUS P5K-E) showing you the digital (Figure 2) and analog (Figure 3) audio connectors.

on-board audio connectorsFigure 1: Connectors found on the rear panel of a motherboard (ASUS P5K-E).

on-board SPDIF connectorsFigure 2: Digital audio connectors (coaxial on the top, optical on the bottom).

on-board analog audio connectorsFigure 3: Analog audio connectors.

The number of analog connectors you will find on your motherboard will depend on how many audio channels your motherboard has (2, 4, 6 or 8) – by the way, “channels” means “outputs for individual speakers,” and 5.1 and 6 are synonyms, as 7.1 and 8 are also synonyms; these are different ways of saying the same thing. On the best case (eight channels – a.k.a. 7.1 format) you will have six connectors like portrayed in Figure 3. The color code used by analog audio jacks is the following:

  • Pink: Mic in
  • Blue: Line in
  • Green: Front speakers out
  • Black (or dark blue on some older boards): Rear speakers out
  • Orange: Center/subwoofer out
  • Gray: Middle speakers out

On motherboards with just two audio channels you will find only the pink, blue and green jacks. On some motherboards with four or six channels you won’t find the black and orange jacks. In this case the blue jack is used for both line in and rear speakers out, and the pink jack is used for both mic in and center/subwoofer speakers out. Of course this configuration isn’t the ideal, as whenever you want to use any of these jacks for another function (for instance, connect a microphone to talk on Skype) you will have to manually remove one plug (the speaker plug) and install another plug (the microphone plug) and switching them again later (after you finished using Skype).

Also some motherboards with eight audio channels do not provide the gray connector, allowing only 5.1 analog speakers to be connected directly to the motherboard. In this case if you want to use all the eight channels you will need to connect your motherboard to a 7.1 home theater receiver or digital speakers using the SPDIF (i.e., digital) connection.


Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.