What Is PCM Audio?
PCM stands for Pulse-Code Modulation. It is the most basic form of digital audio — raw samples of sound captured at regular intervals. Every WAV file, every CD, every digital recording starts as PCM. It is the foundation everything else is built on.
How PCM Works
A microphone converts sound waves into an electrical signal. An analog-to-digital converter (ADC) measures that signal at regular intervals — these measurements are samples. Each sample is a number representing the amplitude of the sound at that instant. Store those numbers in sequence and you have PCM audio. Play them back through a digital-to-analog converter (DAC) and speakers, and you hear the original sound. The fidelity depends on how often you sample (sample rate) and how precisely you measure (bit depth).
PCM Parameters
Sample rate: How many times per second the audio is measured. CD standard is 44,100 Hz. Video standard is 48,000 Hz. Bit depth: How many bits represent each sample. 16-bit gives 65,536 possible values. 24-bit gives 16.7 million values. More bits mean greater dynamic range and lower noise floor. Channels: Mono is one channel. Stereo is two. Surround sound uses more. These three parameters — sample rate, bit depth, and channels — determine everything about the PCM audio quality and file size.
Where PCM Is Used
Audio CDs: 16-bit, 44.1 kHz stereo PCM. WAV files: Usually PCM in a RIFF container. AIFF files: Usually PCM in an IFF container. Blu-ray: Supports PCM up to 24-bit, 192 kHz. Professional recording: All interfaces capture PCM from microphones. HDMI audio: PCM is the uncompressed audio stream. Phone calls: 8-bit, 8 kHz PCM (low quality by design). USB audio: Digital audio interfaces transmit PCM to your computer.
PCM vs Compressed Audio
PCM is uncompressed. Every sample is stored as-is. Lossy codecs (MP3, AAC) start from PCM and discard data to shrink the file. Lossless codecs (FLAC, ALAC) start from PCM and compress without losing data. The decoded output of a lossless codec is identical to the original PCM. The decoded output of a lossy codec is an approximation. PCM is the starting point and the reference against which all compression is judged.
When You Need PCM
Recording: Your audio interface captures PCM. Editing: DAWs work with PCM internally. Mastering: Final masters are PCM before encoding to distribution format. Testing and quality assurance: Compare compressed audio against the PCM original. Any time maximum quality matters and file size does not. For storage and distribution, compress PCM into FLAC (lossless) or MP3/AAC (lossy).