Sound is vibration traveling through air as pressure waves. When a wave reaches a microphone, it moves a diaphragm, and that movement becomes an electrical signal. Digital audio is the process of turning that continuously varying signal into numbers a computer can store and process.
Sampling: measuring amplitude at fixed intervals
The key step is sampling: measuring the amplitude, or strength, of the wave at fixed instants in time using an analog-to-digital converter. The rate of those measurements is the sample rate. The Nyquist theorem explains the fundamental rule: to represent a signal accurately, it must be sampled at least twice per cycle of its highest frequency. Sampling too slowly produces aliasing, where high frequencies reappear as false lower ones.
Sample rate: 44.1 kHz and 48 kHz
Two sample rates became standards: 44.1 kHz, the rate used for audio CDs, and 48 kHz, common in video production. Both are far enough above the upper range of human hearing to represent it cleanly. The choice between them is usually about matching the rest of a production, not about one sounding better than the other.
Bit depth: 16-bit and 24-bit
Bit depth describes how precisely each sample's amplitude is measured. With more bits, each sample can take more possible values, which gives a wider dynamic range between the quietest and loudest sounds that can be represented. 16-bit audio is standard for distribution; 24-bit is a common working choice during recording and editing, where its extra headroom is useful.
PCM: uncompressed samples
PCM, or pulse-code modulation, is the direct form of this idea: a stream of samples, each stored as a number. There is no cleverness, no compression, just the measured waveform, sample after sample. WAV and AIFF files typically hold PCM audio.
Why uncompressed audio takes storage
Because PCM stores every sample, it is large. A stereo recording at a common CD rate produces hundreds of thousands of numbers per second, and file size grows directly with duration. That is why compressed formats such as MP3 and AAC exist: they carry the same music in far fewer bytes, at the cost of discarding detail that most listeners will not notice. Uncompressed audio remains the natural choice for recording, editing, and archiving, where keeping every sample matters more than saving space.