SLOPE-OVERLOAD DISTORTION:
If the slope of the analog signal x(t) is much higher (steep) than that of the approximated signal xq(t) over a long duration then xq(t) will not follow x(t) at all as shown in Figure
The difference between x(t) and xq(t) is called the slope-overload distortion or the slope-overload error. Thus, slope-overload error occurs when the slope of x(t) is much higher than xq(t).
GRANULAR NOISE:
When the input signal x(t) is relatively constant in amplitude with time, the approximated signal xq(t) will hunt above and below x(t) as shown in Figure. This leads to a noise called granular noise.
It increases with increase in step size δ. To reduce granular noise, the step size should be as small as possible. However, this will increase slope-overload distortion.