The Commodore 64 rocked the first audio interface in 1982, essentially a three-voice, three-oscillator hardware synth. Only a decade later, the Creative Labs Sound Blaster 16 brought CD-quality (16-bit 44.1kHz) recording to home computers for the first time. It used analogue-to-digital conversion (ADC) and vice-versa (DAC) to record and playback sounds.
Conversion is done by 'sampling' analogue sound waves a number of times per second, expressed in kHz -- 44.1kHz is 44,100 samples per second. The fidelity, or depth, of each sample is expressed in 'bits', or the amount of ones & zeros the computer can use to encode the sample's volume -- 16-bit is 65,535 potential levels. The transparency or character of the sound is then determined by the quality of the audio interface's components.
Understanding the Main Types of Interfaces