Change Request Summary: Missing TD Renderer File Format

Document Information

• Specification: TS 26.258 v19.1.0
• CR Number: 0008
• Category: A (mirror corresponding to a change in an earlier release)
• Release: Rel-19
• Work Item: IVAS_Codec

Change Request Details

Reason for Change

The binary file format for the TD (Time Domain) binaural renderer was missing from the specification, making it difficult for implementers to understand and use the TD binaural renderer file.

Summary of Change

This CR adds the missing binary file format specification for the TD binaural renderer by introducing a new Table 3G in clause 5.10.

Technical Contribution

TD Binaural Renderer Binary File Format (New Table 3G)

The CR defines a comprehensive binary file format structure for the TD renderer with the following key components:

Basic Parameters (Offsets 0-12)

• Filter method: TDREND_HRFILT_Method_BSplineModel (value 0)
• Latency value and scaling factor
• UseItdModel flag: Indicates if ITD (Interaural Time Difference) model is used
• Sampling rate: 16, 32, or 48 kHz
• Filter length (K)

B-Spline Model Parameters (Offsets 14+)

• Elevation basis functions (P): Number and knot sequence
• Azimuth parameters: For each elevation, includes:
• Number of azimuth basis functions
• Azimuth start index
• Azimuth knot sequence with scaling factor

Alpha Weights (Variable Offsets)

• Number of alpha weights (AlphaN)
• Scaling factor
• Alpha weights for both left and right channels (AlphaN * K elements each)

Azimuth B-Spline Shapes

• Number of unique azimuth B-spline shapes (N_azim)
• For each shape:
• Number of elements
• Scaling factor
• Shape elements
• Number of segment samples
• Shape indices and sampling factors for each elevation knot point

Elevation B-Spline Parameters

• B-spline lengths and start indices (4 coefficients)
• Number of elevation spline shape elements (N_elev)
• Scaling factor and shape elements
• Number of elevation segment samples

Energy Parameters

• Scaling factor for impulse response energy
• Energy values for left and right channels (3 * AlphaN elements each, corresponding to HRTF_MODEL_N_SECTIONS = 3)

Optional ITD Model Parameters (if UseItdModel = 1)

When ITD modeling is enabled, additional parameters are included:

• ITD Elevation Parameters:
• Number of elevations (P_ITD)

• ITD elevation knot sequence with scaling factor

• ITD Azimuth Parameters:

• Number of ITD azimuth basis functions (Q_ITD)
• Azimuth knot sequence for ITD

• B-spline lengths and start indices (4 coefficients)

• Weight Parameters:

• Number of weight elements (WN)
• Scaling factor

• Weight elements (W)

• ITD B-Spline Shapes:

• Azimuth B-spline shape elements (N_azim_ITD) with scaling
• Number of azimuth segment samples
• Elevation B-spline lengths and start indices (4 coefficients)
• Elevation B-spline shape elements (N_elev_ITD) with scaling
• Number of elevation segment samples

Integration with Existing File Format

The new Table 3G integrates with the existing HRTF binary file structure defined in the specification:
- Uses the same header format (Table 3A) with "IVASHRTF" identifier
- Uses the same entry header format (Table 3B) with renderer type HRTF_READER_RENDERER_BINAURAL_OBJECTS_TD
- Input audio configuration is always BINAURAL_INPUT_AUDIO_CONFIG_UNDEFINED for TD renderer
- Can be combined with other renderer types in the same binary file

Technical Notes

• All filter values are represented in fixed-point format
• The notation refers to equation (7.2-6) in clause 7.2.2.2.2 of the referenced specification
• The format supports variable-length data structures with explicit size parameters
• Scaling factors are provided throughout to enable proper fixed-point arithmetic