Thread: Soundcard FAQ
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Old 9th December, 2002, 04:14 PM
Aedan Aedan is offline
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Join Date: September 2001
Location: Europe
Posts: 13,075

General questions

What is a soundcard?
A soundcard is typically a plug in daughterboard that provides various chips that can convert digital information into a signal that speakers and headphone can reproduce.

What's the difference between onboard sound and a soundcard?
In an ideal world, there would be no difference. Alas, we do not live in an ideal world! Often onboard sound has been added with little regard to anything but cost. This often means that it performs poorly. Poorly could mean muffled sound, poor bass, a high level of noise or a blatent inability to do what it's meant to do. Often onboard sound has less in the way of features compared to a soundcard.

Some soundcards also suffer from the same problems as onboard sound, but these are generally the very cheap generic parts. Generally, the more expensive a soundcard is, the better it performs.

Does the use of a soundcard make any difference?
Depending on what you wish to use your soundcard for, you may find a different soundcard is more suitable. Often soundcards designed for gaming do not reproduce sound as accurately or with the same level of quality as a soundcard designed for sound recording. A soundcard designed for sound recording will often not have the same type of acceleration required for gaming, despite generally being of higher quality. Decide what you want your soundcard to do before you buy it!

What is on a soundcard?
A soundcard is typically made up of several parts. However, generally there are two main parts, a Digital Controller and a CODEC. The Digital Controller is the interface to the computer, and the CODEC is the interface to the outside world.

What is a CODEC?
The abbreviation CODEC stands for COder/DECoder. The CODECs job in life is to convert one form of data into another form. It's also a generic term, so it is applicable to many things. In terms of sound, the following are the most common uses.

In terms of physical hardware on a soundcard, a CODEC is the device that turns the digital signal into an analog signal your speakers can handle. It can also convert an analog signal into a digital one, so the computer can deal with things like a microphone or a signal on the linein jack.

In terms of software, a CODEC is a piece of code which converts one form of data into another. For example, an MP3 player has a CODEC in, which converts the MP3 data into audio data the soundcard can play. Some CODECs can convert both ways - for instance, some MP3 CODECS can convert MP3 data into audio, and audio into MP3. If you do not have the correct CODEC for the sound you are trying to play, you cannot play it!

What is a Digital Controller?
The Digital Controller deals with all the computery stuff. It handles talking to the rest of the computer, and taking orders from the CPU. It is responsible for getting the information for the sound from the rest of the computer, doing whatever is necessary, and then passing it onto the CODEC.

As the Digital Controller is the heart of the soundcard, the features it supports will affect the features of the soundcard. Features like audio acceleration, DirectSound hardware support, wavetable synthesis and more are all handled by the Digital Controller.

What is AC97?
AC97 is a standard for linking a CODEC chip to an Digital Controller chip using just 5 wires. It is to CODEC chips what IDE is to hard disks! It defines how the Digital Controller Chip processor will communicate with the CODEC chip, down to how many bits, what frequency, how to set the volume and lots of other things. This means that any AC97 CODEC can be used with any AC97 capable audio processor.

At the time of writing, the latest AC97 spec (V2.3) supported the following list of features:
  • Up to 4 analog line level stereo inputs
  • Up to 2 analog line level mono inputs
  • Mic input with 20dB boost and programmable gain
  • Dedicated Stereo out (Line out), with support for 4 or 6 channels.
  • Additional Stereo out (Aux out), configurable as line out or headphone out.
  • Mono output for speakerphone or mono speaker.
  • 16 bit minimum, with support for 18 or 20bit converters
  • Optional tone and loudness
  • Optional 3D stereo enhancement
  • Optional input for dedicated voice input
  • Option S/PDIF for digital output
  • Optional Jack sensing
  • Support for 8Khz, 11.025Khz, 16Khz, 22.05Khz, 32Khz, 44.1Khz and 48KHz sampling rates.
  • Better than 85dB of dynamic range
  • Better than 17.64kHz frequency response
  • Less than -70dB THD and Noise

On the other hand, it does not specify how the AC97 Digital Controller will appear to the computer. This means that although the AC97 CODEC and AC97 link are standard features, each manufacturer can do what they like with the Digital Controller side. Hence, although manufactuers may use the same CODEC chip, the Digital Controller will provide the addition features such as hardware acceleration.

What is a mixer?
The mixer on a soundcard is the device that collects the various sounds together and mixes them into a signal to send to the speakers. It also acts as a selector for the recording system, choosing which sound source will be recorded.