PCM
Also known as: .pcm file, Pulse-Code Modulation, raw audio
PCM (Pulse-Code Modulation) is raw, uncompressed digital audio — the actual samples of the sound wave with no compression at all. It is the highest-fidelity form and the largest, and it is the underlying audio inside WAV and AIFF files. Lossy formats like MP3 are built by compressing PCM.
- Raw, uncompressed audio samples
- The largest format; perfect fidelity
- The audio inside WAV and AIFF
The raw form of digital audio
PCM is how analog sound becomes digital: the waveform is measured thousands of times a second and each measurement stored as a number. Nothing is compressed or discarded, so PCM is a perfect digital copy — and the biggest possible audio file for a given recording.
Almost every other format starts here. WAV and AIFF are essentially containers around PCM, while MP3, AAC, and Opus are PCM run through compression to save space.
Why size is the trade-off
Because it stores every sample in full, raw PCM is enormous compared with a lossy file — many times the size of an MP3 of the same length. That fidelity is essential for recording and editing but wasteful for casual listening.
For sharing or storing on a phone, converting PCM (or its WAV/AIFF wrappers) to MP3 cuts the size sharply with no loss most listeners can hear.