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2.2 Dither

2.2.1 Basics

The requantization (renewed quantization of already quantized signals) to limited word-lengths occurs repeatedly during storage, format conversion and signal processing algorithms. Here, small signal levels lead to error signals which depend on the input. Owing to quantization, nonlinear distortion occurs for low-level signals. The conditions for the classical quantization model are not satisfied anymore. To reduce these effects for signals of small amplitude, a linearization of the nonlinear characteristic curve of the quantizer is performed. This is done by adding a random sequence d(n) to the quantized signal x(n) (see Fig. 2.17) before the actual quantization process. The specification of the word-length is shown in Fig. 2.18. This random signal is called dither. The statistical independence of the error signal from the input is not achieved, but the conditional moments of the error signal can be affected [Lip92, Ger89, Wan92, Wan00].


  

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