Decoded PCM Output
Decoded PCM output sends reconstructed audio samples to the sound system after decoding occurs in the player or an earlier component.
After a decoder reconstructs audio, its output is usually PCM sample values for the next processing stage. A receiver that detects PCM is being given those values rather than the original compressed soundtrack to decode.
Follow a lossless music example to see where preservation can change.
Trace the samples, not just the output label
Consider 24-bit stereo FLAC at 44.1 kHz, a player with a volume setting of one half, and an output fixed at 48 kHz:
| Stage | Audio representation or operation |
|---|---|
| FLAC source | Compressed description of the original integer samples |
| Decode | Restore those samples into a working representation |
| Volume | Multiply their amplitudes by 0.5 |
| Rate conversion | Calculate the signal at 48,000 positions per second |
| Output formatting | Pack the result for the device's PCM interface |
Lossless decoding restores the source values. The next steps intentionally make another output representation. The PCM label alone cannot tell you whether those steps occurred.
A source sample of +0.6 becomes +0.3 under half gain. If a fractional result cannot fit the final integer grid exactly, rounding/dither becomes another conversion decision. Rate conversion also changes the sequence's positions and count while preserving its intended duration.
The properties of the delivered PCM format
| Output property | Why it is needed |
|---|---|
| Sample rate | Defines when each frame is presented |
| Channel layout/order | Associates values with intended positions |
| Number representation | Specifies integer or float interpretation |
| Storage size and valid precision | Defines how meaningful bits occupy sample words |
A 24-bit presentation can occupy 32-bit words. A six-channel output also needs named roles; an array size of six is insufficient to establish where the center belongs.
For a block of 480 sample frames at 48 kHz, playback time is 10 ms, regardless of how many channels the frame contains. A device consumes complete frames on that timeline.
Lossy decoders produce PCM too
MP3 and other lossy codecs reconstruct their encoded approximation as PCM. Sending those samples uncompressed to an amplifier does not restore the missing original data, but it can avoid another lossy encoding.
The decoded representation describes the current signal. Its source history must be obtained earlier in the path.
Place an immersive render deliberately
An object-aware player can render spatial content into speaker-channel PCM or binaural ear signals. Those can be useful finished spatial outputs. They no longer give a later receiver the source's original object instructions to adapt again.
A supported metadata-bearing path such as Dolby MAT can instead carry the relevant audio and spatial information onward. It should not be confused with ordinary channel PCM.
For an Emby session, record which source was reconstructed and which gain, layout, rate, or spatial operation followed. That explains a PCM result as a sequence of decisions rather than as a verdict that compression quality or immersive content must have been lost.