International organisation for standardisation organisation internationale de normalisation

4.2.2MPEG-D USAC

Max Neuendorf, FhG, presented

m23737

Proposed Corrections to ISO/IEC 23003-3:2012 USAC Text and associated Reference Software

Daniel Fischer, Max Neuendorf, Philippe Gournay, Andreas Niedermeier

The contribution proposes changes to USAC text and Reference Software. The changes to the USAC text are such that

• 
  The text is aligned to the reference software
  
• 
  The text is unambiguous such that a “clean room” USAC decoder can be build.
  

The identified errors and corrections can be summarized as:

• 
  Some PVC variables are not defined in some “corner case” situations
  
• 
  There are inconsistences in variable nomenclature
  
• 
  There is an update of the USAC encoder and decoder figures
  
• 
  Remove all instances of 960-frame length, which is a copy/paste error from earlier Audio specification text.
  
• 
  Correction normalization factor in FAC decoding
  
• 
  Explicit transmission of arbitrary samplingFrequency
  
• 
  Other misc. editorial clarifications
  

It was the consensus of the Audio Subgroup to take the proposed changes to USAC text and issue them as a DCOR, perhaps with a 1-month editing period such that the DCOR ballot closes after the April MPEG meeting.

The changes with respect to the USAC Reference Software are:

• 
  Bug in short blocks with max_sfb=0 causes the spectrum from the previous block to be retained and used.
  

This bug has already been corrected in the USAC Reference. It was the consensus of the Audio Subgroup that this correction must be done.

The changes with respect to the USAC text and Reference Software are:

• 
  The LPC0 coefficent set is not initialized in the case that the first frame of a USAC program is an LPD mode frame. The proposed correction is to define the default “mean LSF values.”
  

There is already code in the Reference Software that implements this, but it is not activated. It is the consensus of the Audio Subgroup to incorporate the text changes into the DCOR text (see above) and to make the corrections to the USAC Reference Software.