# How does DPCM work in digital systems?

#### FabulouSS

Joined Feb 5, 2019
10
Hello!

I can not figure out the implementation of DPCM in a digital system. I have an 8-bit ADC, the output of which is a digital signal (discretized and quantized) - this is PCM. I don’t know how to make DPCM from PCM.

My questions are as shown below:

1. In the diagram below, there is a quantizer - why is it needed if the signal is already quantized before it?
2. Also, I do not quite understand what a predictor is. In some sources, this is a simple one-measure delay line (sample).
3. What method can be used in the entropy encoder for compression?

Thanks for attention!

#### KeithWalker

Joined Jul 10, 2017
2,872
Hello!

I can not figure out the implementation of DPCM in a digital system. I have an 8-bit ADC, the output of which is a digital signal (discretized and quantized) - this is PCM. I don’t know how to make DPCM from PCM.

My questions are as shown below:

1. In the diagram below, there is a quantizer - why is it needed if the signal is already quantized before it?
2. Also, I do not quite understand what a predictor is. In some sources, this is a simple one-measure delay line (sample).

3. What method can be used in the entropy encoder for compression?

Thanks for attention!
It's all here:
https://en.wikipedia.org/wiki/Differential_pulse-code_modulation

#### FabulouSS

Joined Feb 5, 2019
10
What is the entropy coding algorithm (Q in scheme1/scheme2)?

#### KeithWalker

Joined Jul 10, 2017
2,872
What is the entropy coding algorithm (Q in scheme1/scheme2)?

This looks like homework. We do not do homework for students.

#### FabulouSS

Joined Feb 5, 2019
10
I will try to communicate in order to be understood!

I have assembled such a circuit according to the model (see Pic. #1).
So that at the output of the DPC modulator there would be at least 1 bit less (taking into account the sign bit) than with ordinary PCM, I had to increase the sampling frequency by 10 times! Explanations on the chart (see Pic. #2).

In this scheme, I did not add an entropy encoder, because I don’t know what formula should be encoded. Where could I be wrong? Although it seems to me that everywhere.

#### ScottWang

Joined Aug 23, 2012
7,378
Is this a homework ?

#### FabulouSS

Joined Feb 5, 2019
10
Is this a homework ?
No, this is not homework. However, this question arose in the process of studying additional materials on the subject.

#### crutschow

Joined Mar 14, 2008
32,875
No, this is not homework. However, this question arose in the process of studying additional materials on the subject.
In this forum, anything that pertains to the formal study of a subject is classified as "Homework".