Multichannel Audio
Multichannel audio carries separate sound channels for a defined playback arrangement.
A six-channel English soundtrack and a six-channel French soundtrack are two tracks, each containing a complete multichannel presentation. Channels are the separate signals within that presentation, such as front left, center, or surround right.
Keeping those signals separate lets a mix place sound around the listener. It also gives playback software meaningful components to combine when the listening system has fewer outputs.
Six channel values at the same instant
In a conventional 5.1 presentation, a single time position contains six values. An illustrative frame might be:
| Channel role | Sample value at this instant |
|---|---|
| Front left | +0.10 |
| Front right | +0.12 |
| Center | +0.60 |
| LFE | +0.05 |
| Left surround | −0.20 |
| Right surround | +0.25 |
The values do not have to match. At this moment, the center contains a stronger signal, but a different scene can use other channels more heavily. All six advance on the same sample timeline, keeping their combined presentation aligned.
A compressed codec can exploit similarities between channels to store them efficiently. Separate decoded channels do not imply that the file stores six literal uncompressed arrays. The codec reconstructs their values and provides the layout describing their meaning.
Count, layout, order, and routing each do a job
- Count says how many signals exist.
- Layout says which roles they represent.
- Order associates those roles with array positions or buffers.
- Routing sends those signals to the available outputs.
Six arbitrary recording stems are not automatically a 5.1 soundtrack. Likewise, six properly decoded channel waveforms routed using the wrong order can place dialogue behind the listener. The channel-order page follows this mapping explicitly.
Adapt the presentation to the listening system
A surround receiver can keep the principal channels separate and route bass according to its speaker configuration. A stereo television needs a downmix. That operation combines center and surround contributions into the left/right result; it does more than discard unused array positions.
This adaptation explains an Emby session that starts with a 5.1 source but reaches the output as stereo. The source description remains six-channel even though that particular listening presentation has two channels.
For object-based audio, spatial descriptions can accompany a compatible channel presentation. A renderer uses that additional information to make an output for the system. Channel decoding, layout conversion, and object rendering therefore solve related but distinct parts of turning stored sound into a listening arrangement.