Variable Rate ADPCM Based on Explicit Noise Coding
1983; Institute of Electrical and Electronics Engineers; Volume: 62; Issue: 3 Linguagem: Inglês
10.1002/j.1538-7305.1983.tb04410.x
ISSN2376-7154
Autores Tópico(s)Wireless Communication Networks Research
ResumoThis paper discusses a variable bit rate speech coding system based on explicit coding of the reconstruction noise in ADPCM (differential pulse code modulation with adaptive quantization). If the ADPCM bit rate is R bits/sample, PCM coding of its noise using an average bit rate of R n bits/sample provides the receiver with the possibility of operating at any bit rate in the range R to R + max{R n }. Using R values in the range 2 to 5, and R n values in the range 0 to 3, we compare the performance of the (R + R n )-bit system with that of conventional (R + R n )-bit ADPCM. If noise coding is based on instantaneous R n -bit quantization of its samples with an optimized step size, the signal-to-noise ratio performance is comparable to that of conventional ADPCM for R n = 1, but it deteriorates significantly for R n > 1. With non-instantaneous noise coding, the performance can exceed that of conventional ADPCM for any R n > 1, if R > 2. This is due to a variable bit allocation algorithm that quantizes noise samples with differing resolutions, while maintaining a constant total bit rate in every block of 4 ms. The algorithm does not require the transmission of any extra side information. It can also be regarded as a way of improving the performance of ADPCM coding at a single bit rate of R + R n bits/sample.
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