Dolby Atmos Filters

Master Formats

Transform supports the following Dolby Atmos master formats:

Dolby Atmos Master Format (DAMF). This is the native format produced by the Dolby Atmos mastering tools.
Broadcast WAV format (BW64) containing Audio Definition Model (ADM) metadata. This is the format required for iTunes delivery.
Material Exchange Format (MXF) containing an Immersive Audio Bitstream (IAB). This is the standard for Atmos delivery within an IMF package.

The following composition will extract an Atmos track from an IMF package and output a WAV/ADM master:

---
input:
  container:
  - name: imf
    audio:
    - name: stereo
    - name: surround
    - name: atmos
output:
  container:
  - name: bw64
    type: 'wav '
    audio:
    - route:
        name: atmos

{
  "input": {
    "container": [
      {
        "name": "imf",
        "audio": [
          {
            "name": "stereo"
          },
          {
            "name": "surround"
          },
          {
            "name": "atmos"
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "bw64",
        "type": "wav ",
        "audio": [
          {
            "route": {
              "name": "atmos"
            }
          }
        ]
      }
    ]
  }
}

Encoding

The Dolby Digital Plus JOC (Joint Object Coding) ec3j encoder supports the following (required) configuration properties:

Property	Value	Description
ChannelConfiguration	integer	Channel configuration for CBI content: `0` 9.1.6 `1` 7.1.4 `2` 5.1.4
BitRate	integer	Allowable bitrates: `384000`, `448000`, `640000` `768000`
IntegratedLoudness	number	Integrated audio loudness in `LUFS`. This value represents either the ungated, level gated or speech gated loudness based on user preference.
IntegratedLoudnessRange	number	Loudness range in `LU`.
SamplePeak	number	Peak audio sample value in `dBFS`.
TruePeak	number	True peak value in `dBTP`.
DynamicRangeLineModeProfile	integer	`0` none `1` film standard compression `2` film light compression `3` music standard compression `4` music light compression `5` speech compression
DynamicRangeRFModeProfile	integer	`0` none `1` film standard compression `2` film light compression `3` music standard compression `4` music light compression `5` speech compression
DownMixMode	integer	Specifies the stereo down mix mode: `0` not indicated `1` ProLogic `2` Stereo `3` ProLogic2
LoRoCenterMixLevel	integer	Specifies the center channel level for a conventional (LoRo) stereo down mix: `0` 1.414 (+3.0 dB) `1` 1.189 (+1.5 dB) `2` 1.000 (0.0 dB) `3` 0.841 (-1.5 dB) `4` 0.707 (-3.0 dB) `5` 0.595 (-4.5 dB) `6` 0.500 (-6.0 dB) `7` 0.000 (-inf dB)
LoRoSurroundMixLevel	integer	Specifies the surround channel level for a conventional (LoRo) stereo down mix.
LtRtCenterMixLevel	integer	Specifies the center channel level for a matrix (LtRt) stereo down mix.
LtRtSurroundMixLevel	integer	Specifies the surround channel level for a matrix (LtRt) stereo down mix.

For example the following will transcode a Dolby Atmos master file to Dolby Digital Plus:

---
input:
  container:
  - name: atmos
    audio:
    - name: a1
output:
  container:
  - name: mp4
    type: 'mp4 '
    audio:
    - route:
        name: a1
      encode:
        type: ec3j
        properties:
          BitRate: 640000
          IntegratedLoudness: -23.0
          IntegratedLoudnessRange: 25.0
          SamplePeak: -5.0
          TruePeak: -4.0

{
  "input": {
    "container": [
      {
        "name": "atmos",
        "audio": [
          {
            "name": "a1"
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "mp4",
        "type": "mp4 ",
        "audio": [
          {
            "route": {
              "name": "a1"
            },
            "encode": {
              "type": "ec3j",
              "properties": {
                "BitRate": 640000,
                "IntegratedLoudness": -23.0,
                "IntegratedLoudnessRange": 25.0,
                "SamplePeak": -5.0,
                "TruePeak": -4.0
              }
            }
          }
        ]
      }
    ]
  }
}

Loudness Measurement

Dolby Atmos encoding requires audio loudness measurements for both object and channel based immersive content.

Dolby Analyzer

Audio loudness measurement is performed in a preperation pass using the Dolby Loudness dala analysis filter. The filter supports the following configuration properties:

Property	Value	Description
MeteringMode	enum	Specifies the loudness measurement mode: `BT1770_1` ungated loudness, `BT1770_2` gated loudness, `BT1770_3` improved true peak, `BT1770_4` higher channel count.
DialogIntelligence	boolean	Indicates whether Dolby Dialogue Intelligence is enabled.

Loudness measurements are added to each sample as a loud analysis element.

Property	Value	Description
momentary_loudness	number	Momentary (400ms) loudness in `LUFS`.
short_term_loudness	number	Short term (3 s) loudness in `LUFS`.
short_term_10s_loudness	number	Short term (10 s) loudness in `LUFS`.
ungated_loudness	number	Integrated ungated loudness in `LUFS`.
level_gated_loudness	number	Integrated level gated loudness in `LUFS`.
speech_gated_loudness	number	Percentage of content detected as speech.
speech_percentage	number	Current range of loudness levels in `LU`.
sample_peak	number	Sample peak signal level in `dBFS`.
true_peak	number	True peak signal level in `dBTP`.

Properties Writer

The properties prop container writer is used to write the analyzer results to a JSON file:

---
input:
  container:
  - name: atmos
    audio:
    - name: a1
output:
  container:
  - name: json
    type: prop
    properties:
      Kind: data
    audio:
    - route:
        name: a1
      filter:
      - type: dala
        properties:
          MeteringMode: BT1770_4
          DialogIntelligence: true

{
   "input": {
      "container": [
         {
            "name": "atmos",
            "audio": [
               {
                  "name": "a1"
               }
            ]
         }
      ]
   },
   "output": {
      "container": [
         {
            "name": "json",
            "type": "prop",
            "properties": {
               "Kind": "data"
            },
            "audio": [
               {
                  "route": {
                     "name": "a1"
                  },
                  "filter": [
                     {
                        "type": "dala",
                        "properties": {
                           "MeteringMode": "BT1770_4",
                           "DialogIntelligence": true
                        }
                     }
                  ]
               }
            ]
         }
      ]
   }
}

The properties writer will produce an output similar to the following:

{
  "audio": [
    {
      "format": "in24",
      "sample_rate": {
        "numerator": 48000,
        "denominator": 1
      },
      "channels": 26,
      "sample": [
        {
          "duration": 1536,
          "analysis": [
            {
              "type": "loud",
              "momentary_loudness": -10.0,
              "short_term_loudness": -12.0,
              "short_term_10s_loudness": -12.0,
              "ungated_loudness": -21.0,
              "level_gated_loudness": -21.0,
              "speech_gated_loudness": -22.0,
              "speech_percentage": 65.0,
              "loudness_range": 25.0,
              "sample_peak": -5.0,
              "true_peak": -4.0
            }
          ]
        }
      ]
    }
  ]
}

Rendering

Dolby Atmos object based audio content can be rendered to standard channel configurations (stereo, 5.1 or 7.1). Rendering allows Atmos content to be encoded in other formats such as AC-3 or AAC.

Atmos Converter

Rendering is implement using the Dolby Atmos converter dacv filter which supports the following properties:

Property	Value	Description
ChannelConfiguration	enum	Output channel configuration: `stereo`, `C_L_R_Ls_Rs_LFE`, `C_Lc_Rc_L_R_Ls_Rs_LFE`. Default is `stereo`.
MeteringMode	enum	Specifies the loudness measurement mode: `none`, `BT1770_1` ungated loudness, `BT1770_2` gated loudness, `BT1770_3` improved true peak, `BT1770_4` higher channel count. Default is `none`.
DialogIntelligence	boolean	Indicates whether Dolby Dialogue Intelligence is enabled. Default is `false`.
Normalization	number	Loudness normalization in `dB`. Default is 0.0 `dB`.

Rendered Loudness

The following composition renders a Dolby Atmos master file to 5.1 surround and measures the audio loudness:

---
input:
  container:
  - name: atmos
    audio:
    - name: a1
output:
  container:
  - name: json
    type: prop
    audio:
    - route:
        name: a1
      filter:
        type: dacv
        properties:
          ChannelConfiguration: C_L_R_Ls_Rs_LFE
          MeteringMode: BT1770_4

{
  "input": {
    "container": [
      {
        "name": "atmos",
        "audio": [
          {
            "name": "a1"
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "json",
        "type": "prop",
        "audio": [
          {
            "route": {
              "name": "a1"
            },
            "filter": {
              "type": "dacv",
              "properties": {
                "ChannelConfiguration": "C_L_R_Ls_Rs_LFE",
                "MeteringMode": "BT1770_4"
              }
            }
          }
        ]
      }
    ]
  }
}

Rendered Encoding

The following composition encodes a Dolby ATMOS master file to Dolby Digital 5.1 with audio normalization:

---
input:
  container:
  - name: atmos
    audio:
    - name: a1
output:
  container:
  - name: mp4
    type: 'mp4 '
    audio:
    - route:
        name: a1
      filter:
        type: dacv
        properties:
          ChannelConfiguration: C_L_R_Ls_Rs_LFE
          Normalization: -1.0
      encode:
        type: 'ec3 '
        properties:
          OutputFormat: ac-3
          BitRate: 128000

{
  "input": {
    "container": [
      {
        "name": "atmos",
        "audio": [
          {
            "name": "a1"
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "mp4",
        "type": "mp4 ",
        "audio": [
          {
            "route": {
              "name": "a1"
            },
            "filter": {
              "type": "dacv",
              "properties": {
                "ChannelConfiguration": "C_L_R_Ls_Rs_LFE",
                "Normalization": -1.0
              }
            },
            "encode": {
              "type": "ec3 ",
              "properties": {
                "OutputFormat": "ac-3",
                "BitRate": 128000
              }
            }
          }
        ]
      }
    ]
  }
}