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# Phase-Aligned Audio

Phase-aligned audio (PAA) uses multiple synchronised MPEG‑1 Layer II audio components (PIDs), each
carrying two audio channels. Together, these components deliver surround sound channels alongside
additional audio services.

## Assignment of PAA Audio Components

Automatic selection of PAA components for a configured [Service Selection](/beam/receiver/decoding/#service-selection) is
currently not supported. Each PAA component must therefore be manually added and configured using the
guidelines below.

Audio components assigned for PAA are identified using three-letter language codes in the language
descriptors, normally defined in ISO 639.

The tables below show how audio components are assigned to audio decoders based on the language
descriptor, and how they should be embedded in the output (for example, SDI audio embedding).

For the first PAA group, the output channel order is as follows:

| Decode Name | Language Descriptors | Intended Output Channels | Output Embedding |
| ----------- | -------------------- | ------------------------ | ---------------- |
| Audio 1     | a,a,a (a,a,b)        | 1 & 2                    | Embedded 1       |
| Audio 2     | a,a,c (a,a,d)        | 3 & 4                    | Embedded 2       |
| Audio 3     | a,a,e (a,a,f)        | 5 & 6                    | Embedded 3       |
| Audio 4     | a,a,g (a,a,h)        | 7 & 8                    | Embedded 4       |

For the second PAA group, the output channel order is as follows:

| Decode Name | Language Descriptors | Intended Output Channels | Output Embedding |
| ----------- | -------------------- | ------------------------ | ---------------- |
| Audio 5     | b,b,a (b,b,b)        | 1 & 2                    | Embedded 5       |
| Audio 6     | b,b,c (b,b,d)        | 3 & 4                    | Embedded 6       |
| Audio 7     | b,b,e (b,b,f)        | 5 & 6                    | Embedded 7       |
| Audio 8     | b,b,g (b,b,h)        | 7 & 8                    | Embedded 8       |

## Configuring PAA Decode and Output

### Configure PAA Decoding

To set up decode of audio components for PAA, follow these steps:

* Configure the Service Selection, selecting a service that includes PAA content.

* From the Parameters section, select the Decoding tab.

* Select the Audio tab to view the audio decode table.

* Use the Add audio decode button or Decode all input audio
  button to create entries in the audio decode table.

* For each audio entry, select an audio PID from the Input drop-down list, based on the language
  descriptors defined in the Assignment of PAA Audio Components
  section above.

* For each PAA audio entry, set the Decode channel configuration to Stereo.

### Configure PAA Output

To set up the output of audio component for PAA, follow these steps:

* Select the Output tab.

* Select the tab for the output type, for example SDI 1.

* Under the Audio tab, click Add all to automatically add all the decoded audio components
  already configured.

* Click Save and Continue to apply change.