International organisation for standardisation organisation internationale de normalisation

Operating Point
ACELP Mode Usage
30 kbps mono	39% ACELP mode MODE_18k4 (64 bits per subframe)
32 kbps mono	32% ACELP mode MODE_18k4 (64 bits per subframe)

The contribution notes that ACELP provides best performance when coding lower bandwith (typically lower bitrate) signals with no more than 4 ACELP pulses. It further discussed the legacy nature of the MODE_20k and MODE_23k2 modes in the context of AMR-WB+ and noted that in USAC the TCX and FD coding modes are more efficient that ACELP MODE_20k and MODE_23k2.

The Chair noted that the bitstreams for 30 kb/s and 32 kb/s mono operation can be uploaded to the SVN server.

Hervé Taddei, Huawei, presented

m16662

Improved Pulse indexing for ACELP fixed codeword

Dejun Zhang, Fuwei Ma, Herve Taddei, Minjie Xie

The contribution extends Huawei’s pulse-indexing proposal of m16338 from the 88th MPEG meeting to other operating modes. It shows that the proposed tool provides additional compression of the ACELP frames of up to 4.4% and overall compression improvement of up to 0.56%.

Philippe Gournay, VoiceAge, questioned whether coding quality will increase based on an increase in compression efficiency of 0.56%. The presenter responded that if many CEs are adopted that provide small improvements the result may be sufficient to produce a significant improvement in audio quality.

The Chair noted that it might be helpful to compile a list of CEs and their overall improvement in compression efficiency. It might also be worthwhile to compile a list of “open issues” that the group agrees are of significant importance.

Huawei will work to provide information on decoding syntax and semantics this week, and to provide a cross-check on the proposal. The proposal will be discussed later in the week.

There was some discussion on error resilience. It was noted that the lower bitrates of USAC might be attractive for mobile transmission using IP packetization.