Change Request Summary: Missing Description of TD Renderer File Format
Document Information
- Specification: TS 26.258 v18.3.0
- CR Number: 0007
- Category: F (Correction)
- Release: Rel-18
- 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 Contributions
TD Binaural Renderer Binary File Format (New Table 3G)
The CR introduces a comprehensive specification for the HR (Head-Related) filters for the TD binaural renderer entries, including:
Basic Parameters
- 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
- Number of elevation basis functions: P
Elevation and Azimuth B-Spline Model Parameters
- Elevation knot sequence (elevKSeq) with length P-2
- For each elevation:
- Number of azimuth basis functions
- Azimuth start index
- Azimuth knot sequence (azimKSeq) including both 0 and 360 degrees
Alpha Weights
- Number of alpha weights (AlphaN)
- Scaling factor for alpha weights
- Alpha weights for both left and right channels (AlphaN * K elements each)
Azimuth B-Spline Shape Parameters
- Number of unique azimuth B-spline shapes (N_azim)
- For each unique shape:
- Number of azimuth B-spline shape elements
- Scaling factor
- Shape elements
- Number of azimuth segment samples
- Azimuth shape indices for each elevation knot point
- Azimuth shape sampling factors
Elevation B-Spline Parameters
- B-spline lengths (4 coefficients)
- B-spline 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 energy of impulse response
- Energy of impulse response for left channel (3 * AlphaN elements)
- Energy of impulse response for right channel (3 * AlphaN elements)
Conditional ITD Model Parameters (if UseItdModel = 1)
When the ITD model is enabled, the following additional parameters are included:
- Number of elevations in ITD model (P_ITD)
- ITD elevation knot sequence (elevKSeqITD) with length P_ITD - 2
- Number of ITD azimuth basis functions (Q_ITD)
- ITD azimuth knot sequence (azimKSeqITD) with length Q_ITD - 3
- Weight W parameters:
- Number of elements (WN)
- Scaling factor
- Weight elements
- Azimuth ITD B-spline parameters:
- Lengths (4 elements)
- Start indices (4 elements)
- Number of shape elements (N_azim_ITD)
- Scaling factor and shape elements
- Number of segment samples
- Elevation ITD B-spline parameters:
- Lengths (4 elements)
- Start indices (4 elements)
- Number of shape elements (N_elev_ITD)
- Scaling factor and shape elements
- Number of segment samples
Integration with Existing Framework
The new Table 3G is integrated into the existing HRTF filter file format structure defined in clause 5.10, which already includes:
- File header format (Table 3A)
- Entry headers (Table 3B)
- HR filters for other renderer types (Tables 3C-3F)
The TD renderer entry follows the same container format with header and raw data structure as other renderer types, maintaining consistency with the specification's overall architecture.