Article

Mistracking in successive PCM/ADPCM transcoders

CNRS-ESE, Gif-sur-Yvette
IEEE Transactions on Communications (impact factor: 1.68). 09/1989; DOI:10.1109/26.31183 pp.843 - 850
Source: IEEE Xplore

ABSTRACT An analysis is presented of the causes of the accumulation of
quantizing noise found in the transient state for successive CCITT
adaptive differential pulse-code-modulation (ADPCM) transcoders
connected synchronously. By decoupling the predictor and quantizer
effect it is proved that, owing to a self-stabilization phenomenon,
narrowband inputs cause local instabilities in the predictor of the
jointly adaptive autoregressive moving-average-prediction/quantization
used in the ADPCM 32-kb/s algorithm. Despite the assured global
stability, these local instabilities are not synchronized at the encoder
and its preceding decoder, and a mistracking occurs which creates
quantizing noise accumulation. The tracking is then shown to be very
sensitive to predictor/quantizer interaction. The discontinuities
introduced in the standardized adaptive quantizer extend the mistracking
problem to wideband inputs. A smoothed quantizer with reduced
inauspicious interaction is proposed to remedy the problem

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Keywords

accumulation
 
adaptive autoregressive moving-average-prediction/quantization
 
ADPCM
 
ADPCM 32-kb/s algorithm
 
discontinuities
 
local instabilities
 
mistracking
 
narrowband inputs cause local instabilities
 
preceding decoder
 
predictor
 
predictor/quantizer interaction
 
quantizing noise
 
quantizing noise accumulation
 
self-stabilization phenomenon
 
sensitive
 
smoothed quantizer
 
standardized adaptive quantizer
 
transient state
 

M. BONNET