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What is Adaptive Delta Modulation?

by Sonali

The Adaptive Delta Modulation technique helped to overcome the problem of granular noise in delta modulation. This method improves the granular noise and slope overload error found in delta modulation.

The adaptive delta modulation technique overcomes the above mentioned problems by providing variable step size according to the input provided.

The quality of output is hampered in case of delta modulation because of fixed step size. In case of a steep slope of a modulating signal a larger step size is needed and vice versa. Due to this we are unable to get the exact value and hence it is required to make the step size adjustable in order to obtain desired result. This is the main advantage and the theory behind Adaptive Delta Modulation. The working of adaptive delta modulation is as in the block diagram.

Explanation of concept

As we have already discussed, the step size of the staircase signal is not fixed and can be changed according to the input signal. In this case we calculate and estimate the present value and previous value difference . The error generated is then quantized depending on value, if sample value is smaller the quantized value will be high or else it will be low.

The logic step size unit is responsible for deciding the output based on quantizer output. Depending upon the quantizer output we can decide the step size. The step size for the next sample will be double when the value of the quantizer output is high. We can reduce the step size if the quantizer output is low.

Comparison between Delta Modulation and Adaptive Delta Modulation

The comparison  of Delta modulation and Adaptive delta modulation are 

  • The main advantage of ADM is that the we cannot fix step size unlike in DM.
  • The ADM is an improvised version of DM which overcomes granular noise and slope overload error.
  • The DM dynamic range is not that wide as in case of ADM.
  • The DM does not utilize the bandwidth effectively as in case of ADM.

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