The reference model selected by MPEG for the forthcoming unified speech and audio codec (USAC) switches between a non-LPC based coding mode (based on AAC) operating in the transform domain and an LPC-based coding mode (derived from AMR-WB+) operating either in the time domain (ACELP) or in the frequency domain (wLPT). Seamlessly switching between these different coding modes required the design of a new set of cross-fade windows optimized to minimize the amount of overhead information sent during transitions between LPC-based and non-LPC based coding. This paper presents the new set of windows which was designed in order to provide an adequate trade-off between overlap duration and time/frequency resolution, and to maintain the benefits of critical sampling through all coding modes.
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