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1 Functions
A CAE-6DF receiver uses the 6DF transform-domain direct sound components and the time-domain of the diffuse field components to compute the first or higher-order Ambisonics representation of an arbitrary Point of View in the represented area of the reconstructed sound field using:
- Demultiplex the input data (the transform-domain direct sound components and the time-domain of the diffuse field components).
- Directional interpolation of transform-domain plane wave components (direct sound components)
- Linear interpolation of time-domain diffuse components
- Inverse transformation of transform-domain plane wave components into time-domain
- Combination of the reconstructed plane wave and diffuse field components
- (Transcoding the result into binaural signals if necessary)
- The output can be first order ambisonics or high order ambisonics specified by multichannel audio data.
2 Reference Model and its operation
Figure 1 depicts the Six Degrees of Freedom Decoder (CAE-6DC) Reference Model.
Figure 1 – Six Degrees of Freedom Decoder (CAE-6DC)
3 I/O data of AI Workflow
Table 1 gives the input and output data of 6DF Decoder.
Table 2 – Input/Output Data of CAE-6DC
Table 6 – Input/Output Data of the Scene-Based 6DF Decoder
| Input | Description |
| Audio Object | 6DF Audio Object Output of 6DF Encoder |
| Direct Gain | Controls the ratio of the direct vs. the diffuse field |
| Position | Position of User’s Head |
| Orientation | Orientation of User’s Head |
| Output | Description |
| Audio Object | Output of 6DF Decoder which allows rendering in different formats (including 5.1, 7.1, 7.1.4, 11.4, 22.2, HOA, Binaural) |
4 Functions of AI Modules
The Functions of the AIMs required by 6DF Decoder are specified in Table 3.
Table 2 – Functions of AI Modules of 6DF Decoder
| AI Modules | Functions |
| 6DF Demultiplexing | Demultiplexes the 6DF Bitstream. |
| Audio Decompression | Restores the audio waveforms pertaining to the diffuse field . |
| Triplet Select | Selects the three closest microphone arrays’ indices. |
| Interpolation Coefficients Calculation | Calculates the interpolation coefficients given the position of the listener’s head and the closest triplets. |
| Plane Wave Parameter Interpolation | Interpolates the amplitude and direction of plane waves based on the listener’s Position and Orientation. |
| Plane Wave Synthesis | Reconstructs the interpolated plane wave, based on 6DF interpolation (Frequency Domain). |
| Linear Interpolation | Interpolates the diffuse field audio waveform using a linear combination of individual waveforms of diffuse field. |
| Inverse STFT | Reconstructs the direct field audio waveform from frequency domain to time domain. |
| Direct/Diffuse Mix | Mixes the direct and diffuse field based on the Listener-selected direct gain. |
| 6DF Interpolation | Generates an approximation of the Audio Scene Descriptors in a position that was not captured by a Microphone Array. |
| Sound Field Rotation | Rotates the sound field based on the Listener’s head orientation. |
| Audio Rendering Module | Converts time-domain sound field into the audio payload of loudspeakers/headphones. |
| Binaural Transcoding | Transcodes from the Ambisonics format to the binaural format when necessary. |
| Loudspeaker Transcoding | Transcodes from the Ambisonics format to the loudspeaker format when necessary. |
5 I/O Data of AI Modules
Table 4 – Input/Output Data of AI Modules
| AI Modules | Input Data | Output Data |
| 6DF Demultiplexing | Audio Object | Compressed Diffuse Dominant Dominant Sparse Plane Wave
Device Scene Geometry |
| Audio Decompression | Compressed Diffuse Field | Decompressed Diffuse Field |
| Triplet Select | Decompressed Diffuse Field,
Dominant Plane Wave, Microphone Array Indices |
Selected Time-Domain Diffuse Field, Selected Dominant Plane Wave Parameters |
| Interpolation Coefficients Calculation | Listener/head Position, Scene Geometry | Interpolation Coefficients |
| Plane Wave Parameter Interpolation | Selected Direct Dominant Sparse Plane Wave Decomposition, Interpolation Coefficients | Interpolated Frequency-Domain Direct Dominant Sparse Plane Wave Decomposition |
| Plane Save Synthesis | Interpolated Frequency-Domain Direct Dominant Sparse Plane Wave Decomposition | Interpolated Frequency-Domain Direct Dominant Field |
| Linear Interpolation | Selected Time-Domain Diffuse Dominant, Interpolation Coefficients | Interpolated Diffuse Field Dominant |
| Inverse STFT | Interpolated Frequency-Domain Direct Dominant Field | Interpolated Time-Domain Direct Dominant Field |
| Direct/Diffuse Mix | Interpolated Time-Domain Direct Dominant Field, Interpolated Diffuse Field Dominant, Direct Gain | Interpolated Sound Field |
| 6DF Interpolation | Interpolation Parameters
Selected TD Diffuse Field Selected Dominant Plane Wave Parameters |
TD Interpolated Diffuse Sound Field
TD Interpolated Direct Sound Field
|
| Sound Field Rotation | Interpolated Sound Field, Head Orientation | Rotated Sound Field |
| Audio Rendering Module | Selection
Point of View TD Interpolated Total Sound Field |
Audio Object (Headphone)
Audio Object (Loudspeaker) |
| Headphone Transcoding | Rotated Sound Field, HRTF | Binaural Representation of the Sound Field |
| Loudspeaker Transcoding | Rotated Sound Field, HRTF | Loudspeaker Representation of the Sound Field |
6 AIW, AIMs, and JSON Metadata
Table 5 – AIW, AIMs, and JSON Metadata
| AIW | AIM | Name | JSON |
| 6DF-6DC | Six Degrees of Freedom Decoder | File | |
| CAE-6DX | 6DF Demultiplexing | File | |
| CAE-DCM | 6DF Decompression | File | |
| CAE-ICC | Interpolation Coefficients Calculation | File | |
| CAE-TPS | Triplet Select | File | |
| CAE-PWI | Plane Wave Parameter Interpolation | File | |
| CAE-PWS | Plane Wave Synthesis | File | |
| CAE-LIP | Linear Interpolation | File | |
| CAE-ISF | Inverse STFT | File | |
| CAE-DDX | Direct/Diffuse Mix | File | |
| CAE-SFR | Sound Field Rotation | File | |
| CAE-6DI | 6DF Interpolation | File | |
| CAE-ARM | Audio Rendering Module | File |
7. Reference Software
The 6DF Encoder Reference Software can be downloaded from the MPAI Git.
8. Conformance Testing
| Receives | 6DF Audio Object | Shall validate against the Audio Object schema. The Qualifier shall validate against the Audio Qualifier schema. The values of any Sub-Type, Format, and Attribute of the Qualifier shall correspond with the Sub-Type, Format, and Attributes of the Audio Object Qualifier schema. |
| Produces | Audio Object (Headphone) | Shall validate against the Audio Object schema. The Qualifier shall validate against the Audio Qualifier schema. The values of any Sub-Type, Format, and Attribute of the Qualifier shall correspond with the Sub-Type, Format, and Attributes of the Audio Object Qualifier schema. |
| Audio Object (Loudspeaker) | Shall validate against the Audio Object schema. The Qualifier shall validate against the Audio Qualifier schema. The values of any Sub-Type, Format, and Attribute of the Qualifier shall correspond with the Sub-Type, Format, and Attributes of the Audio Object Qualifier schema. |
