International organisation for standardisation

Editorial changes

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  Order of PVC elements in the bitstream as specified in the text vs. the reference code. The proposal is to make the text aligned with the reference code.
  

Changes to Study on DIS test and Reference Software

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  Patch border alignment in SBR harmonic transposer. In rare cases it can be that the patch and parameter band borders are not aligned. In this case, the HF adjustment will not produce a smooth spectral envelope. It is proposed to change the text description and the reference code so that the harmonic transposer operation is identical to the copy-up transposer. This special case never occurred in the CE process or the Verification Test.
  
• 
  Correct SBR buffer management. When the 4:1 SBR mode was adopted, the buffer management parameters were not correctly changed to reflect the impact of the 4:1 sample rate change.
  
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  Similarly, correct the bounds for SBR Inverse Filtering. For this and the previous change, it is proposed to change both the text and the reference software.
  
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  Correct constants used for LSP coefficient interpolation for each ACELP sub-frame. The text and the reference code are correct for 1024 frame length (i.e. 4 sub-frames) but are incorrect for 768 frame length (i.e. 3 sub-frames). The proposal corrects the constants for the 3 sub-frame case.
  
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  PCV handling of SBR parameter frame borders. SBR can operate on fixed or variable (+/- 3 slots) frame boundaries. In the text, PVC HF adjustment operate on variable frame boundaries, while the Gain adjustment operates on fixed frame boundaries. It is proposed to align the text with the reference software.
  
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  PVC handling of time smoothing for transitions. The PVC system must reset the time smoothing filter at time slot 0, which may not be the first PVC timeslot (i.e. when using variable framing). The correction impacts both text and reference software. The is an unusual situation and never occurred in the Verification Test.
  

It was the consensus of the Audio subgroup to adopt all proposals in this contribution into the USAC DIS text and the USAC reference software.

Max Neuendorf, FhG, presented

m21260

Additional Corrections to Study on DIS of USAC

Max Neuendorf, Schuyler Quackenbush, Julien Robilliard, Markus Multrus, Philippe Gournay, Andreas Niedermeier

The contribution lists additional defects in the text and software implementation of the USAC specification. The presenter noted that none of the proposed changes impact the decoded waveforms. The corrections are in three different parts:

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  Editorial changes to the DIS proposed by the Audio Chair.
  
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  Additional corrections that came to light in the time since contribution m20389.
  
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  An annex that contains additional supporting information for contribution m20389.
  

The presenter invited interested experts to review corrections proposed in the first bullet item, both in the marked-up DIS paper copy (provided by the Chair) and the DIS text with change control.

The additional information in the last bullet item are contained in this presentation but were already reviewed in the previous contribution.

The proposed corrections in the second bullet item were presented. They are in two categories: corrections to text only and corrections to text and software. All corrections are either editorial or “good engineering practice.” In addition, the presenter proposed to review and revise the USAC specification block diagram.

It was the consensus of the Audio subgroup to adopt all proposals in this contribution into the USAC DIS text and the USAC reference software.