What Is PCM Audio? Encoding, Formats, and Quality

What PCM audio means

PCM audio is uncompressed digital audio. PCM stands for pulse-code modulation. The analog signal from a microphone or other capture source is measured at regular intervals, and each measurement is stored as a number. The result is a plain sequence of samples that a device can play without first decoding a compressed format.

In everyday use, PCM almost always means linear PCM (LPCM). It is the format behind CD audio, most WAV and AIFF files, the audio track many cameras and recorders write, and the signal a TV sends when its digital audio output is set to PCM. Because compression discards nothing, PCM can deliver high quality. Its quality is still limited by the recording itself and by its sample rate and bit depth.

How PCM encoding works

Sample rate is how many times per second the signal is measured. A sample rate can only represent frequencies below half its value. At 44.1 kHz, the CD standard, that ceiling is about 22 kHz, which is above the commonly cited upper limit of human hearing. 48 kHz is the usual sample rate for video and for many video call and streaming devices.

Bit depth is how precisely each sample is stored. 16-bit audio has 65,536 possible values per sample, and 24-bit audio has about 16.7 million. Each extra bit adds roughly 6 dB of theoretical dynamic range. In practice, more bits mean a lower noise floor and more headroom when you record.

Because PCM is uncompressed, its bitrate is fixed. To calculate it, multiply sample rate by bit depth by the number of channels. CD-quality stereo (44,100 samples per second, 16 bits, 2 channels) works out to 1,411.2 kbps, or roughly 10 MB per minute. Stereo at 48 kHz and 24 bits is 2,304 kbps.

Linear PCM vs PCM

In linear PCM, the quantization steps are evenly spaced across the whole range of loudness. Non-linear PCM variants such as μ-law and A-law space the steps unevenly to save data, and they are used mainly in telephony. When a TV, camera, Blu-ray player or audio editor says PCM or LPCM, it means the same linear format. The two labels are interchangeable in consumer settings.

PCM files, raw PCM and codec labels

A PCM audio file is usually a WAV or AIFF file. These are containers: a short header records the sample rate, bit depth, channel count and byte order, and the PCM samples follow. Software reads the header and knows how to play the data.

Raw PCM is the sample data with no header, often saved as .raw or .pcm. To open it, you must enter the correct sample rate, bit depth, channel count, signed or unsigned format and byte order yourself. Wrong settings produce noise, the wrong speed or distorted sound, even though the data itself is intact.

Media tools often list PCM as a codec, with names that describe the sample layout, such as signed 16-bit little-endian. Strictly speaking, no compression is involved. Lossless codecs such as FLAC and lossy codecs such as MP3 and AAC are stored differently, but every one of them is decoded to PCM before it reaches the output device.

Using PCM in recording and playback

Recording with a microphone or camera

Choosing PCM as the recording format keeps exactly what the input device captured. That includes background noise, room echo and clipping. PCM preserves those problems rather than fixing them, so the setup before recording matters more than the format.

• Match the sample rate to the project: 48 kHz is the common choice for video, and 44.1 kHz for music meant for audio-only release.
• Use 24-bit when the device offers it, so a modest input level still leaves headroom for loud moments.
• Set the input level so peaks stay clearly below the maximum. Clipped PCM cannot be repaired later.
• Reduce background noise at the source, because PCM records it as faithfully as the voice.
• Check the free storage space, since PCM files are much larger than compressed recordings.

PCM output settings on a TV

On a TV, the PCM audio output setting means the TV decodes the soundtrack itself and sends plain PCM to the output device, such as a soundbar or receiver. Any compressed format in the source, such as Dolby Digital, is converted before it leaves the TV.

Bitstream, also labelled passthrough on some devices, sends the encoded soundtrack unchanged so the soundbar or receiver can decode it. Auto usually lets the TV choose based on what the connected device reports it supports. What Auto actually selects depends on the model and software version, so verify the result rather than assuming it.

• Choose bitstream or passthrough when your receiver or soundbar decodes surround formats and you want it to handle them.
• Choose PCM when the connected device cannot decode a format, when sound cuts out or is silent in bitstream mode, or when you use a simple stereo device.
• Choose Auto when the connection negotiates correctly and you would rather not switch modes manually.
• After changing the setting, check the format indicator on the soundbar or receiver if it has one.

LG TVs and other brands commonly offer options such as Auto, PCM and Passthrough for digital sound output. The exact names and their location in the menus vary by model and firmware, so check the manual or on-screen help for your specific set.

Limits and related questions

Is PCM audio good?

PCM is a lossless representation of the samples it contains, so it is the reference that other formats are measured against. It does not make a recording sound better than its source. A noisy microphone or a low-quality compressed stream converted to PCM keeps its original flaws. Higher sample rates and bit depths increase file size, and they only help if the rest of the chain, from the microphone to the speakers, can use the extra detail.

Raw vs PCM in device menus

The word raw has two meanings. In file handling, raw PCM means headerless sample data. In some players and TV menus, Raw refers to passing the original encoded bitstream through without decoding, which is the opposite of the PCM option. Read the menu description to confirm which meaning applies.

Optical, HDMI ARC and eARC

A standard optical connection carries two-channel PCM. Surround sound over optical requires a compressed bitstream, so setting the TV to PCM on that connection typically results in stereo. Standard HDMI ARC has a similar two-channel PCM limit. eARC and direct HDMI connections to a receiver can carry multichannel LPCM.

Because PCM keeps everything the microphone captured, a recording can hold more background sound than you expect. Check where your recording app or device saves files and whether it uploads or syncs them anywhere. Do not assume local-only storage.