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I read that in adaptive delta modulation, we have a block for step size control (diagram below) which takes into account the one bit quantizer output in a feedback loop and modulates it, the intent being to modulate step size to keep up with fluctuations in the message signal. I had a few doubts in this regard.

1] How does it do that? The 1 bit quantizer output is either +delta or -delta, and based on it, how is it possible for the block (Logic for step size control) to know whether to amplify delta or reduce delta to keep up with variations of the message signal?

2] At receiver side, we again have the same block for modulating the received decoded bit (diagram 2). Now, how does the logic block at the receiver side align with the one at the transmitter side? That is, after decoding the received bit as +delta or -delta, how does the receiver know whether to reduce it or amplify it as per the same logic used in transmitter side?

Diagram 1

Diagram 2

Any insights or references would be appreciated.

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    $\begingroup$ When there is a string of several + or - in a row, the step size is increased. When it alternates the step is decreased. $\endgroup$ – IanJ Apr 13 at 23:44

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