Linear PCM (LPCM)
Linear PCM represents digital audio as regularly spaced sample values with uniform amplitude steps.
A signed integer LPCM sample is a direct amplitude value. If the stored code is twice as large, its represented amplitude is twice as large. Linear pulse-code modulation uses this linear relationship, unlike companded formats that assign finer and coarser amplitude spacing in different parts of their range.
There is no compressed-audio prediction or transform to undo before interpreting the sample values.
Two stereo sample frames as stored bytes
Assume signed 16-bit samples, little-endian storage, and interleaved left/right channels. Two sample frames contain:
| Time position | Left | Right | Four stored bytes |
|---|---|---|---|
| 0 | +1,000 | −1,000 | E8 03 18 FC |
| 1 | +2,000 | −2,000 | D0 07 30 F8 |
Each two-byte signed code is the amplitude for one channel at that time. To turn the eight bytes into correctly timed samples, the reader still needs the format description: sample rate, signedness, precision/storage size, byte order, and channel layout.
A WAV or AIFF supplies such a description with its sample data. Their different wrappers do not inherently change the represented sound.
Count the uncompressed payload
At 48 kHz, each channel advances through 48,000 samples every second. With tightly packed 24-bit samples and six channels, each frame uses 144 bits:
48,000 × 24 × 6 = 6.912 Mbit/s.
The rate follows directly from the sample representation. Unlike compressed bitrate, it does not decrease during a simple or quiet passage. All sample positions still occupy their storage.
| LPCM example | Raw audio payload |
|---|---|
| 44.1 kHz, 16-bit, stereo | 1.4112 Mbit/s |
| 48 kHz, 24-bit, 5.1 | 6.912 Mbit/s |
| 96 kHz, 24-bit, 7.1 | 18.432 Mbit/s |
A wider storage word changes the payload calculation. For example, 24 valid bits carried in 32-bit words occupy more space without increasing recorded precision. Sample formats develops that distinction.
The samples can come from several earlier representations
A lossless decoder can restore the PCM values that its encoder preserved. A lossy decoder produces its encoded approximation as PCM. Both results can enter an ordinary sample-processing/output stage, where gain, mixing, or resampling operate on numbers.
Thus a receiver's PCM indication describes the delivered representation. The original library track may have been FLAC, a movie codec, or LPCM itself. To assess preservation, follow what happened before those values reached the output, rather than treating direct sample representation as evidence of a particular recording history.