The sound card (also called audio card) is a necessary component of MPC. It is an adapter for computer sound processing. The sound card has three basic functions:

The first is the music synthesis pronunciation function;

The second is the mixer (Mixer) function and the digital sound effects processor (DSP) function;

The third is the input and output functions of analog sound signals.

There are two methods of music synthesis.

One is the frequency modulation (FM) synthesis method. The FM synthesis method synthesizes simple sounds of multiple frequencies into composite sounds to simulate the sounds of various musical instruments. The FM synthesis method was used in the early days. The sound produced by this method has less timbre and poor sound quality.

The other is the wavetable synthesis method. This method is to first record the sounds of various real musical instruments, then digitally process them to form waveform data, and then store various waveform data in read-only memory. During pronunciation, the waveform data of the selected instrument is found through a table lookup, and then processed through modulation, filtering, and re-synthesis to form a stereo sound for pronunciation. The size of the ROM capacity for storing sound samples has a great influence on the wavetable synthesis effect.

The function of the mixer is to combine sounds from different sources such as music synthesizers, CD-ROMs, and microphone inputs (MIC) and then output them. The mixer is included in every sound card . The digital sound effects processor processes digitized sound signals to obtain the required sound effects (reverberation, delay, chorus, etc.). The digital sound effects processor is a function of high-end sound cards.

The analog sound input and output functions are mainly A/D and D/A conversion. Generally, sound signals are analog signals, and computers cannot process analog signals. After the sound signal is input, the analog signal must be converted into a digital signal and then processed by the computer. Since the speaker can only accept analog signals, the sound card must convert the digital signal into an analog signal before outputting it.

Two parameters commonly used to indicate the performance of a sound card are the sampling rate and the number of data bits after converting analog quantities into digital quantities (referred to as the number of quantization bits). The sampling rate determines the frequency response range. The three standards and sampling frequencies for sound sampling are: voice effect (11 kHz), music effect (22 kHz), and high-fidelity effect (44.1 kHz). The highest sampling rate of the current sound card is 44.1KHz. The number of bits used to store and record the sound amplitude after each sampling of the sound wave is called the number of sampling bits. The number of sampling bits for a 16-bit sound card is 16. The number of quantization bits determines the dynamic range of music. There are two types of quantization bits: 8-bit and 16-bit. An 8-bit sound card has only 256 levels of sound from the lowest to the highest, while a 16-bit sound card has 65536 high and low levels.

The sound information processed by the sound card is stored in the form of files in the computer. The standard digital audio file used by Windows is called a wave file with the extension WAV; sound files with the extension VOL are mainly used in DOS programs; files with the extension MID are used to store MIDI-like sound information; it is more economical than WAV files space. The storage capacity of a sound file is equal to the sampling frequency × the number of sampling bits × the number of channels.