The sound board contains circuitry to accept sound through the Microphones, convert to digital format and record on the hard disk. It has the circuitry to accept input from the CD player (which has CD disk) or DVD player (which has DVD disk) and play the sound through the speakers. If the sound is Stereo sound it is split into two channels – left and right. There is circuitry for connections of MIDI instruments such as synthesizer to the MIDI IN Port of the sound card.

The main IC chip of the sound card is the Digital signal processor (DSP). The DSP is somewhat like the small microprocessor and ROM and RAM are attached to it.

The Sound card has the following connections or jacks
1) MIC in
2) Line in
3) CD audio in
4) Speaker out
5) Line out
6) MIDI instrument in

The Recording section of sound card.
Your sound can be recorded on the hard disk. You can speak into the MIC. The MIC converts sound into analog electrical signals. This is converted to digitized form by the Analog to Digital converter IC. The digital signal processor finally stores the sound file into RAM buffer and then it is saved on to the hard disk.

You can play the music through the synthesizer connected to the MIDI port. The sound is processed by the DSP and again stored on hard disk and through the RAM.

The Playback section of the Sound card.
The CD audio or DVD audio is connected internally from the CD drive or DVD drive by a connector cable to the sound card. Inside the sound card the Mixer IC chip mixes sound signal from the CD, DVD, MIDI instruments and outputs through the speaker.

Bench marking sound Boards
Bench marking is the parameters by which you can compare the performance of various sound cards available in the market.

Unlike other components of the PC, the sound card has many analog benchmarks rather than digital.

1. Decibels. This is the measure of loudness. It is the measure of the gain or attenuation of the sound card.

2. Frequency response . It is the range of frequencies that the sound board will handle uniformly. The sound board should produce same amount of power across the whole of the frequency range. But sound boards having difficulty reproducing
Sounds at the higher or lower frequencies do not have good frequency response, in that, bass and treble ranges might sound weak. The frequency response is denoted by a graph.

3. Signal to noise ratio. A good quality sound card should have a higher signal to noise ratio. The signal to noise ratio is the ratio, expressed in Decibels, of the maximum undistorted signal power to the electronic noise produced by the sound card.

4. Total Harmonic distortion. The lower the value of total harmonic distortion of the sound card the better it is. This is the measure of unwanted harmonics produced by the sound card. Every instrument produces harmonics but if mixed with unwanted harmonics it will not sound realistic.

5. Intermodulation distortion. When several tones are mixed together intermodulation harmonics are generated. This gives harsh overtones. The intermodulation distortion is the measure of unwanted intermodulation. A lower percentage indicate a better board

6. Sensitivity. It is the measure of the ratio of the amplitude of the input signal that will produce the maximum undistorted signal at the output with volume at the maximum. Sensitivity does not measure the fidelity of the sound board.

7. Gain. It is simply the ratio expressed in dB of the output power to the input power of the board.

Sound board can be full duplex or single duplex. In modern communication technologies, the sound has to be received through the microphone and played back through the speakers simultaneously. Full duplex is required in such modern communication technologies as the Internet Phone, Web phone and communication tools etc.