30 Jun 2018

Slope Overload Distortion and Granular (Idle Noise), Quantization Noise in Delta Modulation

Slope Overload Distortion and Granular (Idle Noise)

Slope overload distortion and granular (idle noise) are the two major drawbacks of delta modulation.
So here we are going to discuss both of these drawbacks of delta modulation-
Watch the Complete Video Here-

Slope Overload Distortion

This distortion is caused due to large dynamic range of the input signal. Because When the input signal rising rate is very high, then the staircase signal cannot approximate it correctly.
So it creates large error between the original input signal X(t) and the staircase approximated signal. This noise (error) is known as slope overload distortion.

Solution of Slope Overload Distortion

The step size must be increased, when the input signal has high Slope. Therefore we use Adaptive Delta Modulation technique where the step size is increased when large dynamic variations are present in the signal X(t), to reduce the quantization errors present in delta modulation. 

Granular Noise (Idle Noise)

This noise (error) occurs when the step size is too large in comparison to small variations in the input signal.
So because of large step size in comparison to the signal having very small variations or constant; error is introduced between the input signal and the approximated staircases signal. This error is known as the granular or idle noise.

Solution of the Granular Noise (Idle Noise)

We can overcome the problem of granular noise by keeping the step size small.

We use this in adaptive delta modulation technique, where the step size is reduced as per the small signal value to reduce the difference between the signal and its approximation (staircase waveform).

Now observe the image shown below-
This image shows the quantisation errors in Delta modulation (slope overload distortion and granular noise).


Slope Overload Distortion, Granular Noise, Drawbacks of Delta Modulation, Quantization errors in delta modulations, limitations of delta modulation
Slope Overload Distortion and Granular Noise in Delta Modulation

As you can see in the image that the shaded part in red color shows the slope overload distortion present in Delta modulation while the shaded region in green color represents the granular noise which is also known as idle noise. Both of these errors (noises) are quantization errors and are present in Delta modulation.

On observing this image carefully you will find that the area shaded in red colour is having large dynamic variations (steep slope) in the input signal, therefore the staircase waveform that is used to approximate this signal cannot approximate it. And the shaded region is the difference between the original signal and it's approximation. Here the small step size which is fixed step size (delta) of the staircase signal can not approximate it properly. So this slope overload distortion is due to large dynamic variations in the input signal.
Now observe another part of this image which shows the granular noise.
You will see here that in this region the input signal is having very small variations or is nearly constant. So in this case, fixed step size of the approximated staircase waveform is very large in comparison to the nearly constant original signal.

So again there is a difference between the original signal and the approximated signal. This difference is shown in green shaded region. This kind of quantization error present in Delta modulation is known as granular noise (idle noise).

NOTE:

Adaptive Delta modulation can solve both the problems (slope overload and granular noise) faced by the Delta modulation by varying its step size according to the signal.

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